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

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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.

No MeSH data available.


Determination of CD4+ and CD8+ leukocyte frequency within intestinal tissues from FIV-infected cats.Relative to the FIV-uninfected cats (a), FIV-progressor cats show a less discrete germinal center architecture, merging of follicles and patchy, sparsely populated interfollicular T-cell zones (c). T-cell zones of the Peyer’s patches are expanded by CD8+ T-cells in FIV-progressor cats (d), relative to dense discrete CD8+ cell aggregates within tissues of the uninfected cats (b). Intestinal villus lamina propria of biopsies from FIV-progressor cats is nearly completely depleted of CD4+ leukocytes relative to uninfected cats (e,g,i). Interestingly, intestinal tissues from FIV-progressor cats show greater numbers of villus CD8+ T relative to uninfected cats (f,h,j).
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pone.0175327.g007: Determination of CD4+ and CD8+ leukocyte frequency within intestinal tissues from FIV-infected cats.Relative to the FIV-uninfected cats (a), FIV-progressor cats show a less discrete germinal center architecture, merging of follicles and patchy, sparsely populated interfollicular T-cell zones (c). T-cell zones of the Peyer’s patches are expanded by CD8+ T-cells in FIV-progressor cats (d), relative to dense discrete CD8+ cell aggregates within tissues of the uninfected cats (b). Intestinal villus lamina propria of biopsies from FIV-progressor cats is nearly completely depleted of CD4+ leukocytes relative to uninfected cats (e,g,i). Interestingly, intestinal tissues from FIV-progressor cats show greater numbers of villus CD8+ T relative to uninfected cats (f,h,j).

Mentions: Intestinal Peyer’s patches were available for evaluation from the three FIV-progressor cats for IHC, but not from the LTNP due to the absence of a Peyer’s patch in the cryopreserved section of intestinal tissue. For the FIV-progressor cats, IHC analysis for CD4+ leukocyte distribution in Peyer’s patches demonstrated sparsely populated and poorly demarcated interfollicular T-cell zones that occasionally merged with one another relative to the densely populated and discrete T-cell zones from uninfected cats (Fig 7a and 7c). Peyer’s patches from FIV-infected cats demonstrated a subjective increase in the number of CD8+ T cells in germinal centers and interfollicular regions and a distribution pattern similar to that of CD4+ cells (unevenly distributed) (Fig 7b and 7d). When examining the intestinal mucosa of uninfected cats, CD4+ leukocytes were distinctly present in the middle third of villi, and formed dense clumps, the density of which tapered towards the villus tips (Fig 7e). There was a notable and statistically significant reduction of CD4+ leukocytes in the villous lamina propria of intestinal mucosal tissues from FIV progressor cats relative to the uninfected cats, consistent with CD4+ cell depletion (Fig 7g and 7i). The distribution of CD8+ T cells in Peyer’s patches from uninfected cats was characterized by scattered small aggregates of positive cells evenly distributed throughout the length of the villi (Fig 7f). A distinction was not made between lamina proprial and intraepithelial dwelling CD8+ T cells. Interestingly, intestinal tissues from FIV-progressor cats revealed a marked and statistically significant increase in the number of CD8+ T cells throughout the villi compared to uninfected cats (Fig 7h and 7j). Intestinal biopsies from the LTNP cat demonstrated villus CD4+ leukocyte counts indistinguishable from uninfected cats, and a slight, but statistically significant increase in villus CD8+ T cells, similar to the FIV-progressor cats (Fig 7i and 7j).


Peripheral and central immune cell reservoirs in tissues from asymptomatic cats chronically infected with feline immunodeficiency virus
Determination of CD4+ and CD8+ leukocyte frequency within intestinal tissues from FIV-infected cats.Relative to the FIV-uninfected cats (a), FIV-progressor cats show a less discrete germinal center architecture, merging of follicles and patchy, sparsely populated interfollicular T-cell zones (c). T-cell zones of the Peyer’s patches are expanded by CD8+ T-cells in FIV-progressor cats (d), relative to dense discrete CD8+ cell aggregates within tissues of the uninfected cats (b). Intestinal villus lamina propria of biopsies from FIV-progressor cats is nearly completely depleted of CD4+ leukocytes relative to uninfected cats (e,g,i). Interestingly, intestinal tissues from FIV-progressor cats show greater numbers of villus CD8+ T relative to uninfected cats (f,h,j).
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Related In: Results  -  Collection

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pone.0175327.g007: Determination of CD4+ and CD8+ leukocyte frequency within intestinal tissues from FIV-infected cats.Relative to the FIV-uninfected cats (a), FIV-progressor cats show a less discrete germinal center architecture, merging of follicles and patchy, sparsely populated interfollicular T-cell zones (c). T-cell zones of the Peyer’s patches are expanded by CD8+ T-cells in FIV-progressor cats (d), relative to dense discrete CD8+ cell aggregates within tissues of the uninfected cats (b). Intestinal villus lamina propria of biopsies from FIV-progressor cats is nearly completely depleted of CD4+ leukocytes relative to uninfected cats (e,g,i). Interestingly, intestinal tissues from FIV-progressor cats show greater numbers of villus CD8+ T relative to uninfected cats (f,h,j).
Mentions: Intestinal Peyer’s patches were available for evaluation from the three FIV-progressor cats for IHC, but not from the LTNP due to the absence of a Peyer’s patch in the cryopreserved section of intestinal tissue. For the FIV-progressor cats, IHC analysis for CD4+ leukocyte distribution in Peyer’s patches demonstrated sparsely populated and poorly demarcated interfollicular T-cell zones that occasionally merged with one another relative to the densely populated and discrete T-cell zones from uninfected cats (Fig 7a and 7c). Peyer’s patches from FIV-infected cats demonstrated a subjective increase in the number of CD8+ T cells in germinal centers and interfollicular regions and a distribution pattern similar to that of CD4+ cells (unevenly distributed) (Fig 7b and 7d). When examining the intestinal mucosa of uninfected cats, CD4+ leukocytes were distinctly present in the middle third of villi, and formed dense clumps, the density of which tapered towards the villus tips (Fig 7e). There was a notable and statistically significant reduction of CD4+ leukocytes in the villous lamina propria of intestinal mucosal tissues from FIV progressor cats relative to the uninfected cats, consistent with CD4+ cell depletion (Fig 7g and 7i). The distribution of CD8+ T cells in Peyer’s patches from uninfected cats was characterized by scattered small aggregates of positive cells evenly distributed throughout the length of the villi (Fig 7f). A distinction was not made between lamina proprial and intraepithelial dwelling CD8+ T cells. Interestingly, intestinal tissues from FIV-progressor cats revealed a marked and statistically significant increase in the number of CD8+ T cells throughout the villi compared to uninfected cats (Fig 7h and 7j). Intestinal biopsies from the LTNP cat demonstrated villus CD4+ leukocyte counts indistinguishable from uninfected cats, and a slight, but statistically significant increase in villus CD8+ T cells, similar to the FIV-progressor cats (Fig 7i and 7j).

View Article: PubMed Central - PubMed

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.

No MeSH data available.