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Published on: June 22, 2016
Viral Reservoirs in Lymph Nodes of FIV-Infected Progressor and Long-Term Non-Progressor Cats during the Asymptomatic
C D Eckstrand1, C Hillman1, A L Smith2
1Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, California, United States of America.
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.
Insights
Feline immunodeficiency virus (FIV) replicates in lymph nodes despite undetectable blood virus, leading to immune decline. Understanding these tissue reservoirs is key to treating FIV infection.
Area of Science:
- Virology
- Immunology
- Veterinary Medicine
Background:
- Feline immunodeficiency virus (FIV) infection in cats shows detectable proviral DNA but undetectable plasma viral RNA during the asymptomatic phase.
- Despite apparent viral latency in peripheral CD4+ T cells, these cells progressively decline in FIV-infected progressor cats.
- This study investigates the discrepancy between peripheral blood viral latency and progressive immunopathology in FIV infection.
Purpose of the Study:
- To explore the dichotomy of peripheral blood viral latency and progressive immunopathology in FIV infection.
- To compare viral replication status, cellular immunophenotypes, and histopathologic features between popliteal lymph nodes (PLNs) and peripheral blood.
- To identify and characterize a long-term non-progressor (LTNP) FIV-infected cat.
Main Methods:
- Real-time RT-PCR, Western blot, and immunohistochemistry to assess viral transcription and protein translation in PLN-derived leukocytes.
- Ex vivo reactivation of replication-competent provirus from PLN-derived leukocytes.
- Flow cytometry to determine CD4+ T cell counts and proportions in peripheral blood and PLNs.
Main Results:
- PLN-derived leukocytes from FIV-infected cats showed active viral gag transcription and protein translation, unlike blood leukocytes where viral RNA was undetectable or intermittent.
- Active viral RNA transcription was detected in PLN-derived CD4+ and CD21+ leukocytes.
- Progressor cats had significantly decreased CD4+ T cell counts in blood and PLNs, while the LTNP cat maintained normal CD4+ T cell counts and had lower proviral loads.
Conclusions:
- Popliteal lymph nodes serve as significant reservoirs for ongoing FIV replication during the asymptomatic phase, despite undetectable viral activity in peripheral blood.
- Understanding tissue-based lentiviral reservoirs is crucial for developing medical interventions to eliminate FIV or prolong the asymptomatic period.
