Ex vivo rectal explant model reveals potential opposing roles of Natural Killer cells and Marginal Zone-like B cells in HIV-1 infection

Abstract

Our understanding of innate immune responses in human rectal mucosal tissues (RM) and their contributions to promoting or restricting HIV transmission is limited. We defined the RM composition of innate and innate-like cell subsets, including plasmacytoid dendritic cells; CD1c + myeloid DCs; neutrophils; macrophages; natural killer cells (NK); Marginal Zone-like B cells (MZB); γδ T cells; and mucosal-associated invariant T cells in RM from 69 HIV-negative men by flow cytometry. Associations between these cell subsets and HIV-1 replication in ex vivo RM explant challenge experiments revealed an inverse correlation between RM-NK and p24 production, in contrast to a positive association between RM-MZB and HIV replication. Comparison of RM and blood-derived MZB and NK illustrated qualitative and quantitative differences between tissue compartments. Additionally, 22 soluble molecules were measured in a subset of explant cultures (n = 26). Higher production of IL-17A, IFN-γ, IL-10, IP-10, GM-CSF, sFasL, Granzyme A, Granzyme B, Granulysin, and Perforin following infection positively correlated with HIV replication. These data show novel associations between MZB and NK cells and p24 production in RM and underscore the importance of inflammatory cytokines in mucosal HIV infection, demonstrating the likely critical role these innate immune responses play in early mucosal HIV replication in humans.

T-cell activation and B-cell interaction signatures in rectal tissues are associated with HIV replication in ex-vivo model of infection

“…Additional significant Reactome pathways included antigen-presenting cell (APC)/B-cell pathways and cytokine/chemokine pathways (Table 1). Previous studies within our lab identified B cells within the gut, specifically CD1c+ B cells, as being associated with p24 production in the rectal explant model [17], and CD1C was also associated with p24 here (log 2 fold = 1.10, P adj = 0.003). Additional DEGs of interest included genes necessary for B-cell–T-cell interactions, such as CD40 (log 2 fold = 0.72, P adj = 0.0004), CD83 (log 2 fold = 0.93, P adj = 0.003), and IL4I1 (log 2 fold = 0.96, P adj = 0.001).…”

“…For the explant challenge, three biopsies from each participant were weighed and challenged with 10 2.8 TCID 50 HIV-1 BaL for 2 h (37 8C, 5% CO 2 ), placed on a collagen raft, and sampled longitudinally, as previously described [17]. Supernatants were collected on days 3, 7, 10, 14, and 18 post-challenge, and stored at À30 8C until p24 was quantified via ELISA (ABL, Inc., Rockville, Maryland, USA; #5447), and normalized to biopsy weight.…”

“…As an alternative strategy to identify signatures within the rectal mucosa associated with support or restriction of HIV replication, we utilized the ex-vivo human rectal explant model of HIV infection. This system was developed to interrogate the earliest immune responses within rectal mucosal tissues after HIVexposure, to evaluate novel anti-HIV therapeutics, and, within our lab, to identify immune cell subsets associated with support or suppression of HIV production [11][12][13][14][15][16][17]. Here, we performed bulk RNAseq transcriptomic analyses on rectal biopsies donated by HIV-negative men (Fig.…”

The rectal mucosal immune environment and HIV susceptibility among young men who have sex with men

“…Three fresh rectal biopsy specimens from each participant were exposed to HIV-1 BaL (10 2.8 TCID 50 in a volume of 250 µL media) for 2 hours, washed extensively, and placed on collagen rafts for the 18-day incubation period, as described in detail previously ( 22 ). Culture supernatant was collected from each well at days 3, 7, 10, 14, and 18 for p24 concentration analysis, and the well was replenished with 700 μl of fresh complete media.…”

The Importance of Regulation in Natural Immunity to HIV

“…NK cells also seem to play a role in the rectal immunity to HIV. A higher frequency of NK cells in rectal mucosa (which resembles that of the FGT, with the lower expression of CD16 and a higher expression of CD56 compared to their blood counterparts) seem to correlate negatively with HIV-1 replication in this tissue, as opposed to MZ B-cells, which frequencies correlate positively with viral replication [ 190 , 197 ]. It was suggested that MZ could contribute to trans-infection of HIV given that as mentioned earlier, these cells can bind to virus particles via surface lectins such as α4β7 and DC-SIGN [ 152 ].…”