Jennifer Johns is an assistant professor in the Department of Comparative Medicine and a veterinary clinical pathologist. She is director of the Diagnostic Laboratory in the Veterinary Service Center. Dr. Johns received her B.S. from UCLA and her D.V.M and later Ph.D. from UC Davis. She completed clinical pathology residency training at UC Davis and obtained board certification from the American College of Veterinary Pathologists. Her background includes years of experience as a clinical veterinarian and as a diagnostic pathologist for domestic, exotic and laboratory animal species. Her primary research focus is in host-pathogen interactions.

Academic Appointments

Administrative Appointments

  • Director, Animal Diagnostic Lab, Veterinary Service Center (2012 - Present)

Honors & Awards

  • Board Certification - Clinical Pathology, American College of Veterinary Pathologists (2007)

Boards, Advisory Committees, Professional Organizations

  • Executive Board member, American Society for Veterinary Clinical Pathology (2012 - Present)

Professional Education

  • Ph.D., University of California, Davis, Comparative Pathology (2011)
  • Residency, University of California, Davis, Veterinary Clinical Pathology (2007)
  • D.V.M., University of California, Davis, Veterinary Medicine (2001)

Research & Scholarship

Current Research and Scholarly Interests

Dr. Johns' primary research work centers on the host immune response to tick-borne bacterial infections, focusing particularly on Granulocytic Anaplasmosis due to Anaplasma phagocytophilum infection. One area of current investigation is the role of interferon signaling pathways in the host response to A. phagocytophilum infection and their relative importance in dictating hematologic and histopathologic alterations, associated cytokine changes, and pathogen dissemination and persistence.

Dr. Johns' collaborative work includes investigation into leukocyte trafficking alterations in animal models of various infectious and inflammatory diseases. As Director of the Animal Diagnostic Lab, she advises on all aspects of clinical pathology in animal species. Her clinical work encompasses novel testing and sampling techniques along with comparative hematology and hematopoiesis.


2014-15 Courses


All Publications

  • Acute phase proteins in healthy goats: Establishment of reference intervals JOURNAL OF VETERINARY DIAGNOSTIC INVESTIGATION Heller, M. C., Johns, J. L. 2015; 27 (2): 177-181


    Acute inflammatory processes can trigger increased production of acute phase proteins (APPs) that can be useful biomarkers of inflammation. APPs are diverse and include proteins involved in coagulation, opsonization, iron regulation, and limitation of tissue injury. Haptoglobin, serum amyloid A, and alpha-1 acid glycoprotein have been proposed as useful APPs in goats. APPs can differ markedly by species, therefore species-specific reference intervals and studies are necessary. The objective of this study was to determine species-specific reference intervals for 4 APPs in goats. Haptoglobin, serum amyloid A, lipopolysaccharide binding protein, and alpha-1 acid glycoprotein were measured in in 54 clinically normal adult goats. APPs were measured using goat-specific commercial enzyme-linked immunosorbent assay kits. Results were analyzed by 1-way analysis of variance to compare sexes and breeding status. Reference Value Advisor was used to calculate reference limits according to the IFCC-CLSI guidelines. Only 1 APP was found to vary in healthy animals; serum haptoglobin was increased in lactating animals and decreased in pregnant does in their second trimester when compared with open, nonlactating does. No sex-based differences were seen for any of the APPs measured. We report normal reference intervals for 4 serum APPs that may be useful as disease markers. Haptoglobin should be interpreted with caution in animals with unknown pregnancy status. Further studies are needed to determine whether these APPs are useful biomarkers in goat disease states.

    View details for DOI 10.1177/1040638715575750

    View details for Web of Science ID 000351590300006

    View details for PubMedID 25776542

  • Unilateral intraocular mastocytosis and anterior uveitis in a dog with subcutaneous mast cell tumors VETERINARY OPHTHALMOLOGY Boostrom, B. O., Good, K. L., Maggs, D. J., Rebhun, R. B., Johns, J. L., Kent, M. S. 2014; 17 (2): 131-138


    A 9-year-old male castrated Scottish terrier was referred to the Radiation Oncology Service at the William R. Pritchard Veterinary Medical Teaching Hospital for palliative radiation therapy of an incompletely excised, recurrent subcutaneous mast cell tumor (MCT) located over the right scapula, and surgical removal of a perianal MCT. Three weeks after initial presentation and prior to the fifth radiation treatment, the patient was presented with cloudiness of the left eye of 3-7 days duration. Ophthalmic consultation revealed 3+ aqueous flare with a dependent, swirling component filling approximately one-third of the anterior chamber. Aqueocentesis was performed under general anesthesia. Cytology revealed mast cells with highly atypical morphology and considered most consistent with neoplasia. The patient died 7 months after pathologic diagnosis of MCT on the right shoulder and 2 months after the cytologic diagnosis of malignant mast cells in the left anterior chamber. To the authors' knowledge, this is the first report of intraocular involvement in a mammal with MCTs, described here as intraocular mastocytosis.

    View details for DOI 10.1111/vop.12041

    View details for Web of Science ID 000332046800009

    View details for PubMedID 23578200

  • Prevalence of Batrachochytrium dendrobatidis in 120 Archived Specimens of Lithobates catesbeianus (American Bullfrog) Collected in California, 1924-2007 ECOHEALTH Huss, M., Huntley, L., Vredenburg, V., Johns, J., Green, S. 2013; 10 (4): 339-343


    The chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been identified as a major cause of the recent worldwide amphibian decline. Numerous species in North America alone are under threat or have succumbed to Bd-driven population extinctions. The American bullfrog (Lithobates catesbeianus) has been reported as a tolerant carrier of Bd. In this report, we used a qPCR assay to test 120 archived American bullfrog specimens collected between 1924 and 2007 in California, USA and Baja California, Mexico. The overall prevalence of Bd infection in this archived population of L. catesbeianus was 19.2%. The earliest positive specimen was collected in Sacramento County, California, USA in 1928 and is to date the earliest positive archived Bd specimen reported globally. These data demonstrate that Bd-infected wild amphibians have been present in California longer than previously known.

    View details for DOI 10.1007/s10393-013-0895-6

    View details for Web of Science ID 000332375100003

    View details for PubMedID 24419668

  • The Systemic Immune State of Super-shedder Mice Is Characterized by a Unique Neutrophil-dependent Blunting of TH1 Responses. PLoS pathogens Gopinath, S., Hotson, A., Johns, J., Nolan, G., Monack, D. 2013; 9 (6)


    Host-to-host transmission of a pathogen ensures its successful propagation and maintenance within a host population. A striking feature of disease transmission is the heterogeneity in host infectiousness. It has been proposed that within a host population, 20% of the infected hosts, termed super-shedders, are responsible for 80% of disease transmission. However, very little is known about the immune state of these super-shedders. In this study, we used the model organism Salmonella enterica serovar Typhimurium, an important cause of disease in humans and animal hosts, to study the immune state of super-shedders. Compared to moderate shedders, super-shedder mice had an active inflammatory response in both the gastrointestinal tract and the spleen but a dampened TH1 response specific to the secondary lymphoid organs. Spleens from super-shedder mice had higher numbers of neutrophils, and a dampened T cell response, characterized by higher levels of regulatory T cells (Tregs), fewer T-bet(+) (TH1) T cells as well as blunted cytokine responsiveness. Administration of the cytokine granulocyte colony stimulating factor (G-CSF) and subsequent neutrophilia was sufficient to induce the super-shedder immune phenotype in moderate-shedder mice. Similar to super-shedders, these G-CSF-treated moderate-shedders had a dampened TH1 response with fewer T-bet(+) T cells and a loss of cytokine responsiveness. Additionally, G-CSF treatment inhibited IL-2-mediated TH1 expansion. Finally, depletion of neutrophils led to an increase in the number of T-bet(+) TH1 cells and restored their ability to respond to IL-2. Taken together, we demonstrate a novel role for neutrophils in blunting IL-2-mediated proliferation of the TH1 immune response in the spleens of mice that are colonized by high levels of S. Typhimurium in the gastrointestinal tract.

    View details for DOI 10.1371/journal.ppat.1003408

    View details for PubMedID 23754944

  • Anaplasma phagocytophilum Dihydrolipoamide Dehydrogenase 1 Affects Host-Derived Immunopathology during Microbial Colonization INFECTION AND IMMUNITY Chen, G., Severo, M. S., Sakhon, O. S., Choy, A., Herron, M. J., Felsheim, R. F., Wiryawan, H., Liao, J., Johns, J. L., Munderloh, U. G., Sutterwala, F. S., Kotsyfakis, M., Pedra, J. H. 2012; 80 (9): 3194-3205


    Anaplasma phagocytophilum is a tick-borne rickettsial pathogen that provokes an acute inflammatory response during mammalian infection. The illness caused by A. phagocytophilum, human granulocytic anaplasmosis, occurs irrespective of pathogen load and results instead from host-derived immunopathology. Thus, characterizing A. phagocytophilum genes that affect the inflammatory process is critical for understanding disease etiology. By using an A. phagocytophilum Himar1 transposon mutant library, we showed that a single transposon insertion into the A. phagocytophilum dihydrolipoamide dehydrogenase 1 gene (lpda1 [APH_0065]) affects inflammation during infection. A. phagocytophilum lacking lpda1 revealed enlargement of the spleen, increased splenic extramedullary hematopoiesis, and altered clinicopathological abnormalities during mammalian colonization. Furthermore, LPDA1-derived immunopathology was independent of neutrophil infection and correlated with enhanced reactive oxygen species from NADPH oxidase and nuclear factor (NF)-κB signaling in macrophages. Taken together, these findings suggest the presence of different signaling pathways in neutrophils and macrophages during A. phagocytophilum invasion and highlight the importance of LPDA1 as an immunopathological molecule.

    View details for DOI 10.1128/IAI.00532-12

    View details for Web of Science ID 000307869100021

    View details for PubMedID 22753375

  • Downregulation of CXCL12 signaling and altered hematopoietic stem and progenitor cell trafficking in a murine model of acute Anaplasma phagocytophilum infection INNATE IMMUNITY Johns, J. L., Borjesson, D. L. 2012; 18 (3): 418-428


    Infection with a variety of bacterial pathogens results in hematopoietic stem and progenitor cell (HSPC) mobilization. The mechanism and kinetics of HSPC mobilization during infection are largely unknown. Previously, we found altered HSPC activity in bone marrow, spleen and blood during infection with Anaplasma phagocytophilum, the agent of granulocytic anaplasmosis. We hypothesized that altered CXCL12/CXCR4 signaling, a central pathway for HSPC homing to, and retention within, the bone marrow, plays a role in infection-induced alterations in HSPC number and trafficking. Mice were infected with A. phagocytophilum. Lineage-cKit+ HSPCs were enumerated and proliferation determined. CXCL12 and CXCR4 mRNA were quantified along with CXCL12 protein, and CXCR4 surface, intracellular and total protein expression in HSPCs was determined. Increased bone marrow proliferation of HSPCs began at 2 d post-infection followed by HSPC mobilization and splenic homing. Proliferation of resident HSPCs contributed to increased splenic HSPC numbers. Bone marrow CXCL12 mRNA and protein levels were decreased at 4-8 d post-infection concurrent with HSPC mobilization. CXCR4 protein parameters were decreased in bone marrow HSPCs throughout 2-6 d post-infection. Reduction of CXCL12/CXCR4 signaling simultaneously occurs with HSPC mobilization from bone marrow. Findings suggest that deranged CXCL12/CXCR4 signaling plays a causal role in HSPC mobilization during acute A. phagocytophilum infection.

    View details for DOI 10.1177/1753425911413794

    View details for Web of Science ID 000304699600005

    View details for PubMedID 21964802

  • Extramedullary Hematopoiesis: A New Look at the Underlying Stem Cell Niche, Theories of Development, and Occurrence in Animals VETERINARY PATHOLOGY Johns, J. L., Christopher, M. M. 2012; 49 (3): 508-523


    Extramedullary hematopoiesis (EMH) is the formation and development of blood cells outside the medullary spaces of the bone marrow. Although widely considered an epiphenomenon, secondary to underlying primary disease and lacking serious clinical or diagnostic implications, the presence of EMH is far from incidental on a molecular basis; rather, it reflects a well-choreographed suite of changes involving stem cells and their microenvironment (the stem cell niche). The goals of this review are to reconsider the molecular basis of EMH based on current knowledge of stem cell niches and to examine its role in the pathophysiologic mechanisms of EMH in animals. The ability of blood cells to home, proliferate, and mature in extramedullary tissues of adult animals reflects embryonic patterns of hematopoiesis and establishment or reactivation of a stem cell niche. This involves pathophysiologic alterations in hematopoietic stem cells, extracellular matrix, stromal cells, and local and systemic chemokines. Four major theories involving changes in stem cells and/or their microenvironment can explain the development of most occurrences of EMH: (1) severe bone marrow failure; (2) myelostimulation; (3) tissue inflammation, injury, and repair; and (4) abnormal chemokine production. EMH has also been reported within many types of neoplasms. Understanding the concepts and factors involved in stem cell niches enhances our understanding of the occurrence of EMH in animals and its relationship to underlying disease. In turn, a better understanding of the prevalence and distribution of EMH in animals and its molecular basis could further inform our understanding of the hematopoietic stem cell niche.

    View details for DOI 10.1177/0300985811432344

    View details for Web of Science ID 000303234900012

    View details for PubMedID 22262354

  • Post-transfusion survival of biotin-labeled allogeneic RBCs in adult horses VETERINARY CLINICAL PATHOLOGY Mudge, M. C., Walker, N. J., Borjesson, D. L., Librach, F., Johns, J. L., Owens, S. D. 2012; 41 (1): 56-62


    Post-transfusion survival of allogeneic RBCs has been reported to be much shorter in horses than in other species. We hypothesized that post-transfusion survival of biotinylated allogeneic equine RBCs would be greater than the survival previously reported from studies using radioactive RBC-labeling techniques.The study objective was to determine post-transfusion survival of N-hydroxysuccinimide (NHS)-biotin-labeled allogeneic equine RBCs transfused into adult horses.Horses were adults and included 5 donors and 5 recipients. All horses were blood-typed, and donors were paired with recipients based upon blood type and crossmatch results. Donor blood was collected in a volume of 4 L into citrate phosphate dextrose adenine-1 and stored for 24 hours, labeled with NHS-biotin, and re-infused into recipients. Post-transfusion blood samples were collected at 15 minutes and at 1, 2, 3, 5, 7, 14, 21, 28, and 35 days. Biotin-labeled RBCs were detected by flow cytometry using streptavidin-phycoerythrin. Post-transfusion survival at 24 hours, lifespan, and half-life of biotinylated RBCs were determined.Mean ± SD survival of biotinylated RBCs at 24 hours post-transfusion was 95 ± 24%; the mean lifespan of transfused allogeneic RBCs was 39 days based on calculation of a linear regression survival curve, and mean post-transfusion RBC half-life was 20 days.Post-transfusion survival of 24-hour stored equine allogeneic RBCs was greater than previously reported but less than that observed for other companion animal species. Mechanisms for the relatively short post-transfusion lifespan of allogeneic equine RBCs remain unknown and warrant further study.

    View details for DOI 10.1111/j.1939-165X.2011.00384.x

    View details for Web of Science ID 000301046700011

    View details for PubMedID 22251607

  • Processing of equine bone marrow using the automated MarrowXpress System: RBC depletion, volume reduction, and mononuclear cell recovery VETERINARY CLINICAL PATHOLOGY Owens, S. D., Burges, J., Johns, J. L., Carrade, D. D., Galuppo, L. D., Librach, F., Borjesson, D. L. 2011; 40 (4): 444-449


    The therapeutic use of bone marrow-derived mononuclear cells (MNCs) and mesenchymal stem cells for the treatment of soft tissue and orthopedic injuries in equine patients is expanding. After collection, bone marrow must be reduced in volume and depleted of RBCs for immediate therapeutic use or to prepare cells for culture or cryopreservation and storage. The MarrowXpress (MXP) System is an automated, closed, sterile system designed to process human bone marrow samples.The purpose of this study was to evaluate the capacity of the MXP System to process equine bone marrow to reduce volume, deplete RBCs, and enhance recovery of MNCs.Bone marrow was collected from 47 horses into 2 60-mL syringes containing heparin and processed using the MXP System. HCT, total nucleated cell (TNC) count, and MNC count were obtained for each sample before and after processing using an Advia 120 hematology analyzer. Volume reduction, RBC depletion, and recovery of TNCs and MNCs were calculated.For equine bone marrow samples, mean values were 73.2% for RBC depletion and 78.0% for volume reduction. TNC count before processing was 2.5 ± 1.2 × 10(7) and after processing was significantly higher at 7.8 ± 3.3 × 10(7) (P < .0001), with a recovery of 68.5 ± 24.5% (mean ± SD). MNC count before processing was 1.1 ± 0.9 × 10(7) and after processing was significantly higher at 3.8 ± 1.9 × 10(7) (P < .0001), with a recovery 73.0 ± 31.5%.The MXP System can reliably reduce volume and deplete RBCs from aspirates of equine bone marrow aspirates. MNCs can be recovered in a reproducible and sterile manner. Further studies evaluating the effects of the MXP System on cell viability, identification of mesenchymal stem cells (MSCs), and the efficacy of MSC expansion are warranted.

    View details for DOI 10.1111/j.1939-165X.2011.00368.x

    View details for Web of Science ID 000298258300011

    View details for PubMedID 22092275

  • Expression and Activity of a Novel Cathelicidin from Domestic Cats PLOS ONE Leonard, B. C., Chu, H., Johns, J. L., Gallo, R. L., Moore, P. F., Marks, S. L., Bevins, C. L. 2011; 6 (4)


    Cathelicidins are small cationic antimicrobial peptides found in many species including primates, mammals, marsupials, birds and even more primitive vertebrates, such as the hagfish. Some animals encode multiple cathelicidins in their genome, whereas others have only one. This report identifies and characterizes feline cathelicidin (feCath) as the sole cathelicidin in domestic cats (Felis catus). Expression of feCath is predominantly found in the bone marrow, with lower levels of expression in the gastrointestinal tract and skin. By immunocytochemistry, feCath localizes to the cytoplasm of neutrophils in feline peripheral blood. Structurally, the mature feCath sequence is most similar to a subgroup of cathelicidins that form linear α-helices. feCath possesses antimicrobial activity against E. coli D31, Salmonella enterica serovar Typhimurium (IR715), Listeria monocytogenes and Staphylococcus pseudintermedius (clinical isolate) similar to that of the human ortholog, LL-37. In contrast, feCath lacks the DNA binding activity seen with LL-37. Given its similarity in sequence, structure, tissue expression, and antimicrobial activity, the cathelicidin encoded by cats, feCath, belongs to the subgroup of linear cathelicidins found not only in humans, but also non-human primates, dogs, mice, and rats.

    View details for DOI 10.1371/journal.pone.0018756

    View details for Web of Science ID 000289404700031

    View details for PubMedID 21533281

  • Salmon poisoning disease in dogs: A satisfying diagnosis VETERINARY JOURNAL Johns, J. L. 2011; 187 (2): 149-150

    View details for DOI 10.1016/j.tvjl.2009.11.006

    View details for Web of Science ID 000288520000004

    View details for PubMedID 20006937

  • Use of an in vitro biotinylation technique for determination of posttransfusion survival of fresh and stored autologous red blood cells in Thoroughbreds AMERICAN JOURNAL OF VETERINARY RESEARCH Owens, S. D., Johns, J. L., Walker, N. J., Librach, F. A., Carrade, D. D., Tablin, F., Borjesson, D. L. 2010; 71 (8): 960-966


    To evaluate N-hydroxysuccinimide (NHS)-biotin labeling of equine RBCs and determine posttransfusion survival of autologous equine RBCs stored in citrate phosphate dextrose adenine-1 (CPDA-1) for 0, 1, 14, and 28 days.13 healthy adult Thoroughbreds.Serial dilutions of biotin and streptavidin-phycoerythrin (PE) were evaluated in vitro in blood collected from 3 horses. One horse was used to determine RBC distribution and recovery. Twelve horses were allocated to 4 groups for in vivo experiments in which blood was collected into CPDA-1. Blood was labeled with biotin and reinfused or stored at 4 degrees C for 1, 14, or 28 days prior to labeling with NHS-biotin and reinfusion. Posttransfusion blood samples were collected 15 minutes and 1, 2, 3, 5, 7, 14, 21, 28, and 35 days after reinfusion. Biotin-labeled RBCs were detected via flow cytometry by use of streptavidin-PE. Posttransfusion lifespan of RBCs and RBC half-life were determined.Optimal biotin concentration was 0.04 pg of biotin/RBC, and the optimal streptavidin-PE ratio was 1.2 microg of streptavidin-PE/1 x 10(6) RBCs. Posttransfusion lifespan of autologous RBCs was 99, 89, 66, and 59 days after storage for 0, 1, 14, and 28 days, respectively. Storage did not result in significant alterations in RBC lifespan. Mean posttransfusion RBC half-life was 50, 45, 33, and 29 days for 0, 1, 14, and 28 days of storage, respectively.Biotin can be used to label equine RBCs for RBC survival studies. Posttransfusion survival of equine autologous RBCs was greater than previously reported.

    View details for Web of Science ID 000280431800015

    View details for PubMedID 20673097

  • Neutrophils exposed to A. phagocytophilum under shear stress fail to fully activate, polarize, and transmigrate across inflamed endothelium AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY Schaff, U. Y., Trott, K. A., Chase, S., Tam, K., Johns, J. L., Carlyon, J. A., Genetos, D. C., Walker, N. J., Simon, S. I., Borjesson, D. L. 2010; 299 (1): C87-C96


    Anaplasma phagocytophilum is an obligate intracellular bacterium that has evolved mechanisms to hijack polymorphonuclear neutrophil (PMN) receptors and signaling pathways to bind, infect, and multiply within the host cell. E-selectin is upregulated during inflammation and is a requisite endothelial receptor that supports PMN capture, rolling, and activation of integrin-mediated arrest. Ligands expressed by PMN that mediate binding to endothelium via E-selectin include sialyl Lewis x (sLe(x))-expressing ligands such as P-selectin glycoprotein ligand-1 (PSGL-1) and other glycolipids and glycoproteins. As A. phagocytophilum is capable of binding to sLe(x)-expressing ligands expressed on PMN, we hypothesized that acute bacterial adhesion to PMN would subsequently attenuate PMN recruitment during inflammation. We assessed the dynamics of PMN recruitment and migration under shear flow in the presence of a wild-type strain of A. phagocytophilum and compared it with a strain of bacteria that binds to PMN independent of PSGL-1. Acute bacterial engagement with PMN resulted in transient PMN arrest and minimal PMN polarization. Although the wild-type pathogen also signaled activation of beta2 integrins and elicited a mild intracellular calcium flux, downstream signals including PMN transmigration and phosphorylation of p38 mitogen-activated protein kinase (MAPK) were inhibited. The mutant strain bound less well to PMN and failed to activate beta2 integrins and induce a calcium flux but did result in decreased PMN arrest and polarization that may have been partially mediated by a suppression of p38 MAPK activation. This model suggests that A. phagocytophilum binding to PMN under shear flow during recruitment to inflamed endothelium interferes with normal tethering via E-selectin and navigational signaling of transendothelial migration.

    View details for DOI 10.1152/ajpcell.00165.2009

    View details for Web of Science ID 000278887800012

    View details for PubMedID 20392928

  • Anaplasma phagocytophilum and Ehrlichia muris induce cytopenias and global defects in hematopoiesis CLINICAL MICROBIOLOGY AND INFECTION Borjesson, D., MacNamara, K., Johns, J., Winslow, G. 2009; 15: 66-67
  • Infection with Anaplasma phagocytophilum Induces Multilineage Alterations in Hematopoietic Progenitor Cells and Peripheral Blood Cells INFECTION AND IMMUNITY Johns, J. L., MacNamara, K. C., Walker, N. J., Winslow, G. M., Borjesson, D. L. 2009; 77 (9): 4070-4080


    Infection with Anaplasma phagocytophilum, a gram-negative, lipopolysaccharide (LPS)-negative, obligate intracellular bacterium, results in multiple peripheral blood cytopenias. We hypothesized that infection with this organism would result in decreased bone marrow (BM) function and shifts in hematopoietic progenitor cells (HPCs) and lineage-committed cells in a well-established murine model of infection. HPCs and lineage-committed progenitors were enumerated in the BM and spleen during acute infection. BM cytokine production and BM CXCL12 expression were determined. Infection resulted in peripheral blood bicytopenia, marked decreases in the number of lineage-committed HPCs in the BM along with concurrent increases in the number of lineage-committed HPCs in the spleen, and a mixed, predominantly myelosuppressive BM cytokine environment. There was significant downregulation of CXCL12 in BM cells that may have been partially responsible for changes in HPC trafficking observed. Changes occurred in the absence of direct pathogen infection of BM cells. Hematopoietic lineage assessment demonstrated that there was loss of erythrocytes and B lymphocytes from the BM along with increased granulopoiesis. These changes were accompanied by splenomegaly due to lymphoid hyperplasia and increased hematopoiesis, most notably erythropoiesis. These changes largely mimic well-described inflammation and endotoxin-mediated effects on the BM and spleen; however, the numbers of peripheral blood neutrophils appear to be independently modulated as granulocytic hyperplasia does not result in neutrophilia. Our findings highlight a well-conserved series of events that we demonstrate can be instigated by an LPS-negative pathogen in the absence of an endotoxin-mediated acute proinflammatory response.

    View details for DOI 10.1128/IAI.00570-09

    View details for Web of Science ID 000269947200058

    View details for PubMedID 19564373

  • What is your diagnosis? Blood smear from an injured red-tailed hawk VETERINARY CLINICAL PATHOLOGY Johns, J. L., Luff, J. A., Shooshtari, M. P., Zehnder, A. M., Borjesson, D. L. 2009; 38 (2): 247-252


    An injured juvenile red-tailed hawk (Buteo jamaicensis) was evaluated at the Veterinary Medical Teaching Hospital at the University of California, Davis. The hawk was quiet, alert, and emaciated, and had a closed comminuted, mid-diaphyseal ulnar fracture. CBC results included heterophilia with a left shift, monocytosis, and increased plasma fibrinogen concentration. The blood smear included rare heterophils containing small, dark blue inclusions approximately 1-2 mum in diameter that ranged from round to coccobacillary in shape and formed variably shaped aggregates; the morphology of the inclusions was suspicious for Chlamydophila or Ehrlichia spp. pathogens. The hawk died, and histopathologic examination of tissues obtained at necropsy found severe multifocal histiocytic and heterophilic splenitis in addition to chronic hepatitis, myocarditis and epicarditis, meningoencephalitis, and airsacculitis. Using immunohistochemistry the presence of Chlamydia/Chlamydophila spp. antigen within multiple tissues was confirmed. Chlamydophila psittaci DNA was demonstrated in whole blood and fresh splenic tissue via real-time PCR. Direct fluorescent antibody staining of air-dried blood smears was positive in rare leukocytes for Chlamydia/Chlamydophila spp. antigen, and immunocytochemical staining of blood smears for Chlamydia/Chlamydophila spp. antigen was focally positive in rare heterophils. These findings may represent the first reported diagnosis of natural avian C. psittaci infection by visualization of organisms in peripheral blood heterophils. Immunocytochemical evaluation of blood smears was valuable in confirming the diagnosis and may be a useful antemortem test to discriminate between bacteria and other inclusions within heterophils.

    View details for DOI 10.1111/j.1939-165X.2008.00091.x

    View details for Web of Science ID 000266603300015

    View details for PubMedID 19228359

  • Avian hematology and related disorders. The veterinary clinics of North America. Exotic animal practice Mitchell, E. B., Johns, J. 2008; 11 (3): 501-?


    Hematology is an essential component of veterinary practice. The interpretation of avian blood cells provides many challenges. Practitioners must be able to recognize normal morphology and function of cells to interpret changes in those cells. This article describes the normal morphology of avian erythrocytes, leukocytes, and thrombocytes. Changes observed in erythrocytes and leukocytes during disease and major differential diagnoses are discussed. A brief overview of avian blood parasites is also presented.

    View details for DOI 10.1016/j.cvex.2008.03.004

    View details for PubMedID 18675731

  • Development of a technique for quantification of reticulocytes and assessment of erythrocyte regenerative capacity in birds AMERICAN JOURNAL OF VETERINARY RESEARCH Johns, J. L., Shooshtari, M. P., Christopher, M. M. 2008; 69 (8): 1067-1072


    To develop a reticulocyte classification scheme, optimize an avian reticulocyte staining protocol, and compare the percentages of reticulocyte types with polychromatophil percentage in blood samples from birds.Blood samples from a red-tailed hawk and 31 ill birds.A single blood sample obtained from a red-tailed hawk (Buteo jamaicensis) was used to optimize the staining protocol. For optimization of the staining protocol, 4 dilutions of whole blood with new methylene blue stain and 4 incubation times were evaluated. From samples submitted for avian CBCs, EDTA-anticoagulated whole blood samples from 31 ill birds were randomly selected and examined to compare polychromatophil and reticulocyte percentages. Reticulocyte staining was performed in all samples by use of a 1:3 (whole blood to new methylene blue) dilution with incubation for 10 minutes at room temperature (approx 22 degrees C); reticulocytes were assessed as a percentage of 1,000 RBCs by 2 independent observers. In Wright-Giemsa-stained blood smears, a polychromatophil percentage was similarly determined.4 avian reticulocyte types were defined: ring-form reticulocytes, aggregate reticulocytes, and 2 subcategories of punctate reticulocytes. A reticulocyte-staining protocol was optimized. Interobserver and intraobserver variations in assessment of reticulocyte and polychromatophil percentages were not significant. A strong positive correlation (Spearman coefficient of rank correlation [rho] = 0.978) was identified between the percentage of polychromatophils and the percentage of ring-form reticulocytes.Results indicated that quantification of ring-form reticulocytes provides an accurate assessment of erythrocyte regenerative capacity in birds.

    View details for Web of Science ID 000258085800014

    View details for PubMedID 18672972

  • Effect of intrathecal amikacin administration and repeated centesis on digital flexor tendon sheath synovial fluid in horses VETERINARY SURGERY Dykgraaf, S., Dechant, J. E., Johns, J. L., Christopher, M. M., Bolt, D. M., Snyder, J. R. 2007; 36 (1): 57-63


    To determine the effect of intrathecal amikacin administration and repeated tenovaginocentesis on the total nucleated cell count (TNCC), total protein (TP) concentration and cytologic characteristics of synovial fluid of the equine digital flexor tendon sheath (DFTS).Randomized, cross-over experimental design.Adult horses (n=8).Synovial fluid was aseptically collected from the DFTS and either 1 mL amikacin sulfate (250 mg/mL) or lactated Ringer's solution (LRS) was injected into the DFTS. Serial synovial fluid samples were obtained at 0, 12, 24, 48, and 72 hours. The opposite treatment was administered to the contralateral DFTS after a washout period of 2 weeks.Treatment increased TP concentration, TNCC, percentage of neutrophils, and neutrophil counts from baseline levels. There was no difference between treatment of the DFTS with amikacin or LRS. Values peaked at 12-24 hours after the initial centesis and then declined toward baseline levels.Injection and repeat centesis of the normal DFTS with 250 mg amikacin or an equivalent volume of LRS resulted in mild increases in synovial fluid analytes from baseline. Synovial inflammation in this study was not accompanied by lameness at the walk and measured analytes returned toward baseline levels within 12-24 hours of first injection.The effect of tenovaginocentesis and intrathecal administration of amikacin or LRS on DFTS synovial fluid values are modest in most horses; however, some horses can develop marked increases in synovial fluid values that may be interpreted as sepsis.

    View details for Web of Science ID 000243428600008

    View details for PubMedID 17214821

  • Lymph node aspirate from a California wine-country dog VETERINARY CLINICAL PATHOLOGY Johns, J. L., Strasser, J. L., Zinkl, J. G., Christopher, M. M. 2006; 35 (2): 243-246


    A 4-year-old, male Golden Retriever was presented to the Veterinary Medical Teaching Hospital at the University of California-Davis with a history of lethargy, inappetance, and vomiting. The patient had generalized lymphadenomegaly, marked thrombocytopenia, mild anemia, and moderate hypoalbuminemia. Moderate to marked histiocytic inflammation and lymphocytic-plasmacytic reactivity of the mesenteric, left popliteal, and right mandibular lymph nodes were diagnosed cytologically. Many macrophages contained granular to amorphous material of a uniform blue color, occasionally in morula formation, suggestive of rickettsial organisms. Exposure to raw trout was subsequently documented, leading to a presumptive diagnosis of salmon poisoning disease (SPD). The patient responded quickly to doxycycline therapy for the causative agent of SPD (Neorickettsia helminthoeca). SPD should be considered as a differential diagnosis for a canine patient with clinical signs of vomiting, diarrhea, lethargy, and lymphadenomegaly; laboratory findings of thrombocytopenia and hypoalbuminemia; and potential exposure to raw fish from an endemic area. The cytologic finding of rickettsial inclusions within lymph node macrophages is reportedly seen within a majority of SPD cases and can be valuable in supporting a clinical suspicion of SPD, as it was in this case.

    View details for Web of Science ID 000238333300019

    View details for PubMedID 16783722

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