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

Abstract

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.

Central and peripheral reservoirs of feline immunodeficiency virus in cats: a review

“…These observations suggested a proliferation of resident of Tfh cells or infiltration of CD8+ T cells into the B cell follicles, although CD8+ T cells are generally restricted from entering B cell follicles. Secondly, in our most recent report, a novel in situ hybridization technique (RNAscope) for detection of FIV RNA identified germinal centres in the mesenteric lymph node, spleen and intestinal Peyer's patches as microanatomical reservoirs of viral transcription in the chronically FIV-infected cat [92].…”

“…Anatomical reservoirs frequently discussed in the HIV field are the brain, gut-associated lymphoid tissue (GALT), lymph nodes and the reproductive tract [13,14,88,91]. Many of these tissues have been investigated as tissue reservoirs in the FIV-infected cat as well, particularly during the acute and early asymptomatic phases of infection [60,62,79,92]. A thorough understanding of tissue reservoir distribution and biology requires an understanding of the early pathogenesis and dissemination of virus.…”

“…Infection of bone marrow cells in naturally infected asymptomatic cats has also been reported, although the identity of infected subsets was not determined [25]. Two recent investigations into tissue reservoirs by our laboratory demonstrated the presence of proviral DNA within the popliteal lymph node, mesenteric lymph node, spleen and mucosa of the small intestines during the late asymptomatic phase of infection (5-6 years post inoculation), in the face of a relatively quiescent or inactive viral harbour replication-competent provirus in spite of relatively quiescent or inactive viral replication in the peripheral blood [79,92,109]. Interestingly, our studies revealed that, firstly, lymph node germinal centres contained an increased frequency of CD3+ T cells compared to uninfected cat tissues.…”

“…While the detection and quantification of these various viral components can provide supportive evidence of viral replication, they do not ultimately prove a cell's ability to produce infectious virus. The 'gold standard assay' for the identification of replication-competent and infectious lentiviral reservoir cells is the ex vivo viral outgrowth assay (VOA) which has been used extensively for investigation of HIV-1 latency in humans [111] and in our laboratory for detection of cells containing transcriptionally silent infectious provirus in cats chronically infected with FIV [84,92]. For assessment of virus infection by VOA, an enriched (purified) cell type such as CD4+ T cells are obtained from an infected individual and are cultured ex vivo.…”

Epigenetic Modulation of CD8+ T Cell Function in Lentivirus Infections: A Review

“…However, in a recent study CD4 + and CD21 + leukocytes were identified as cellular reservoirs for FIV replication which is similar to the subsets identified in HIV infection wherein CD4 + T cells serve as cellular reservoirs and CD21 + B cells serve as extracellular HIV reservoirs [ 48 , 49 ]. The same study identified FIV reservoirs in tissues such as the spleen, the intestine and mesenteric lymph node with B cell follicles as the foci of viral replication in chronically infected cats exhibiting viral latency [ 50 ]. This demonstrates that the FIV model offers the advantage of performing longitudinal infection studies which can be beneficial in understanding tissue viral reservoir dynamics [ 50 ].…”