Peripheral and central immune cell reservoirs in tissues from asymptomatic cats chronically infected with feline immunodeficiency virus.

Feline immunodeficiency virus (FIV) infection in cats results in life-long viral persistence and progressive immunopathology. We have previously described a cohort of experimentally infected cats demonstrating a progressive decline of peripheral blood CD4+ T-cell over six years in the face of apparent peripheral viral latency. More recently we reported findings from this same cohort that revealed popliteal lymph node tissue as sites for ongoing viral replication suggesting that tissue reservoirs are important in FIV immunopathogenesis during the late asymptomatic phase of infection. Results reported herein characterize important tissue reservoirs of active viral replication during the late asymptomatic phase by examining biopsied specimens of spleen, mesenteric lymph node (MLN), and intestine from FIV-infected and uninfected control cats. Peripheral blood collected coincident with harvest of tissues demonstrated severe CD4+ T-cell depletion, undetectable plasma viral gag RNA and rarely detectable peripheral blood mononuclear cell (PBMC)-associated viral RNA (vRNA) by real-time PCR. However, vRNA was detectable in all three tissue sites from three of four FIV-infected cats despite the absence of detectable vRNA in plasma. A novel in situ hybridization assay identified B cell lymphoid follicular domains as microanatomical foci of ongoing FIV replication. Additionally, we demonstrated that CD4+ leukocyte depletion in tissues, and CD4+ and CD21+ leukocytes as important cellular reservoirs of ongoing replication. These findings revealed that tissue reservoirs support foci of ongoing viral replication, in spite of highly restricted viral replication in blood. Lentiviral eradication strategies will need address tissue viral reservoirs.

Viral Reservoirs in Lymph Nodes of FIV-Infected Progressor and Long-Term Non-Progressor Cats during the Asymptomatic Phase.

BACKGROUND: Examination of a cohort of cats experimentally infected with feline immunodeficiency virus (FIV) for 5.75 years revealed detectable proviral DNA in peripheral blood mononuclear cells (PBMCs) harvested during the asymptomatic phase, undetectable plasma viral RNA (FIV gag), and rarely detectable cell-associated viral RNA. Despite apparent viral latency in peripheral CD4+ T cells, circulating CD4+ T cell numbers progressively declined in progressor animals. The aim of this study was to explore this dichotomy of peripheral blood viral latency in the face of progressive immunopathology. The viral replication status, cellular immunophenotypes, and histopathologic features were compared between popliteal lymph nodes (PLNs) and peripheral blood. Also, we identified and further characterized one of the FIV-infected cats identified as a long-term non-progressor (LTNP). RESULTS: PLN-derived leukocytes from FIV-infected cats during the chronic asymptomatic phase demonstrated active viral gag transcription and FIV protein translation as determined by real-time RT-PCR, Western blot and in situ immunohistochemistry, whereas viral RNA in blood leukocytes was either undetectable or intermittently detectable and viral protein was not detected. Active transcription of viral RNA was detectable in PLN-derived CD4+ and CD21+ leukocytes. Replication competent provirus was reactivated ex vivo from PLN-derived leukocytes from three of four FIV-infected cats. Progressor cats showed a persistent and dramatically decreased proportion and absolute count of CD4+ T cells in blood, and a decreased proportion of CD4+ T cells in PLNs. A single long-term non-progressor (LTNP) cat persistently demonstrated an absolute peripheral blood CD4+ T cell count indistinguishable from uninfected animals, a lower proviral load in unfractionated blood and PLN leukocytes, and very low amounts of viral RNA in the PLN. CONCLUSION: Collectively our data indicates that PLNs harbor important reservoirs of ongoing viral replication during the asymptomatic phase of infection, in spite of undetectable viral activity in peripheral blood. A thorough understanding of tissue-based lentiviral reservoirs is fundamental to medical interventions to eliminate virus or prolong the asymptomatic phase of FIV infection.

Diagnostic exercise: High mortality in a flock of chukar partridge chicks (Alectoris chukar) in California.

Mortality of 20% of a flock of 1000 chukar partridge chicks occurred over a 6-week period in Northern California from August to September 2012. Affected birds were 2 to 42 days old and died without premonitory clinical signs or after showing ruffled feathers and anorexia for 24 to 72 hours. Three carcasses were submitted for necropsy, 2 birds had hemorrhagic tracheitis grossly, and all 3 had lymphoplasmacytic and histiocytic myocarditis with myocardial necrosis microscopically. The differential diagnoses and the diagnostic workup to achieve a final diagnosis are discussed. The detection of 2 zoonotic agents in these birds makes this an interesting case from a public health perspective.

Nematode-associated intramural alimentary nodules in pumas are histologically similar to gastrointestinal eosinophilic sclerosing fibroplasia of domestic cats.

Intramural alimentary nodules in the gastric pylorus and proximal duodenum are a common finding in free-ranging pumas (Puma concolor) in North America, and are often associated with the presence of an indwelling nematode (most commonly Cylicospirura spp.). This study compares the histological, histochemical and immunohistochemical appearance of three proximal gastrointestinal nodules in pumas with four cases of eosinophilic sclerosing fibroplasia in domestic cats. Histologically, the pattern of inflammation and repair was strikingly similar, consisting of lamillated anastomosing trabeculae of dense sclerotic collagen with interspersed inflammatory cells and reactive fibroblasts. The stromal trabeculae were histologically reminiscent of osteoid and were uniformly positive for collagenous protein by Masson's trichrome stain and negative for mineralized osteoid deposits with Von Kossa's stain. Trabecular cells expressed osteonectin, but not osteocalcin immunohistochemically. Collectively, these findings are most consistent with a stroma comprised of dense collagenous trabeculae that resembles, but is distinct, from osteoid. Both the puma and domestic cat lesions demonstrated an eosinophilic inflammatory component; however, eosinophils were present in small numbers in the puma nodules relative to the nodules in domestic cats. These entities likely represent a unique and stereotypic gastrointestinal repair response of felids, given their similar histological, histochemical and immunohistochemical profiles.