Rate of AIDS progression is associated with gastrointestinal dysfunction in simian immunodeficiency virus-infected pigtail macaques

Abstract

During HIV/SIV infection, mucosal immune system dysfunction and systemic immune activation are associated with progression to AIDS; however, it is unclear to what extent pre-existing gastrointestinal damage relates to disease progression postinfection. Pigtail macaques (PTM) are an excellent model in which to assess mucosal dysfunction in relation to HIV/SIV pathogenesis, as the majority of these animals have high levels of gastrointestinal damage, immune activation, and microbial translocation prior to infection, and rapidly progress to AIDS upon SIV infection. In this study, we characterized the mucosal immune environment prior to and throughout SIV infection in 13 uninfected PTM and 9 SIV-infected PTM, of which 3 were slow progressors. This small subset of slow progressors had limited innate immune activation in mucosal tissues in the periphery, which was associated with a more intact colonic epithelial barrier. Furthermore, we found that preinfection levels of microbial translocation, as measured by LPS-binding protein, in PTM correlated with the rate of progression to AIDS. These data suggest that pre-existing levels of microbial translocation and gastrointestinal tract dysfunction may influence the rate of HIV disease progression.

Fig. 1. AIDS progression, viremia, and CD4⁺ lymphocyte populations in pigtail macaques during SIV infection

(A) Progression to AIDS in SIV⁺ slow progressors (SP) and SIV⁺ progressors (P). Progression measured as days post infection until AIDS defining illness (*or scheduled euthanasia in SP). (B) Set point viral load measured during chronic infection (>200 days post infection). (C) The percentage of CD4⁺ T cells was measured by flow cytometry, gated on live, singlet, CD3⁺ T cells. Cells measured were from peripheral blood mononuclear cells (PBMC, left), mesenteric lymph nodes (MLN, left center), colon (right, center), and jejunum (right), obtained at necropsy. Horizontal lines represent mean and P-values were calculated using Mann-Whitney nonparametric U test. For multiple comparisons, P-value was adjusted with Bonferroni correction. SIV-uninfected, circles; SIV-uninfected Mane-A1*084⁺, open circles; SIV⁺ Mane-A1*084⁺ slow progressors, open triangles; SIV⁺ progressors, squares; SIV⁺ Mane-A1*084⁺ progressors, open squares.

Fig. 2. Immune activation in the GI tract and periphery is reduced in slow progressors

The amount of immune activation in necropsy tissues was measured by immunohistochemistry staining for MxA, an interferon-responsive protein. (A) Representative MxA stain (brown) in lymph node samples from SIV− (left), SIV+ slow progressors (center), and SIV+ progressors (right). The percent area of tissue quantified as positively stained for MxA in (B) mesenteric lymph node, (C) colon, (D) jejunum, and (E) axillary lymph node. Horizontal lines represent mean and P-values were calculated using Mann-Whitney nonparametric U test. For multiple comparisons, P-value was adjusted with Bonferroni correction. SIV-uninfected, circles; SIV-uninfected Mane-A1*084⁺, open circles; SIV⁺ Mane-A1*084⁺ slow progressors, open triangles; SIV⁺ progressors, squares; SIV⁺ Mane-A1*084⁺ progressors, open squares.

Fig. 3. Peripheral activation is related to colon epithelial damage, which is reduced in slow progressors

The breach/intact ratio in colonic necropsy tissues was measured by immunohistochemical staining for claudin-3, a tight junction protein. Breached epithelium (not stained for claudin) was quantified in relation to intact epithelium (stained for claudin). (A) Representative claudin stain with arrows indicating epithelial breaches. (B) Comparison of colon breach/intact ratio in PTM. (C) The breach/intact ratio significantly correlates with the amount of immune activation, measured by MxA, in the axillary lymph node. (D) The breach/intact ratio significantly correlates with the amount of immune activation in the colon. Correlation determined by Spearman’s rank correlation. Line represents linear regression. Horizontal lines represent mean and P-values were calculated using Mann-Whitney nonparametric U test. For multiple comparisons, P-value was adjusted with Bonferroni correction. SIV-uninfected, circles; SIV⁺ Mane-A1*084⁺ slow progressors, open triangles; SIV⁺ progressors, squares; SIV⁺ Mane-A1*084⁺ progressors, open squares.

Fig. 4. Microbial translocation pre-infection and at necropsy correlate with AIDS progression

Lipopolysaccharide-binding protein (LBP) was measured in plasma as a marker of microbial translocation. (A) The concentration of LBP in plasma prior to infection (left) and at necropsy (right). The plasma LBP concentration (B) pre-SIV infection, and (C) at necropsy, negatively correlates with days until AIDS progression (*or scheduled necropsy in SP). Correlation determined by Spearman’s rank correlation. Line represents linear regression. Horizontal lines represent mean and P-values were calculated using Mann-Whitney nonparametric U test. SIV⁺ Mane-A1*084⁺ slow progressors, open triangles; SIV⁺ progressors, squares; SIV⁺ Mane-A1*084⁺ progressors, open squares.