Exposure to HIV-1 Directly Impairs Mucosal Epithelial Barrier Integrity Allowing Microbial Translocation

Abstract

While several clinical studies have shown that HIV-1 infection is associated with increased permeability of the intestinal tract, there is very little understanding of the mechanisms underlying HIV-induced impairment of mucosal barriers. Here we demonstrate that exposure to HIV-1 can directly breach the integrity of mucosal epithelial barrier, allowing translocation of virus and bacteria. Purified primary epithelial cells (EC) isolated from female genital tract and T84 intestinal cell line were grown to form polarized, confluent monolayers and exposed to HIV-1. HIV-1 X4 and R5 tropic laboratory strains and clinical isolates were seen to reduce transepithelial resistance (TER), a measure of monolayer integrity, by 30–60% following exposure for 24 hours, without affecting viability of cells. The decrease in TER correlated with disruption of tight junction proteins (claudin 1, 2, 4, occludin and ZO-1) and increased permeability. Treatment of ECs with HIV envelope protein gp120, but not HIV tat, also resulted in impairment of barrier function. Neutralization of gp120 significantly abrogated the effect of HIV. No changes to the barrier function were observed when ECs were exposed to Env defective mutant of HIV. Significant upregulation of inflammatory cytokines, including TNF-α, were seen in both intestinal and genital epithelial cells following exposure to HIV-1. Neutralization of TNF-α reversed the reduction in TERs. The disruption in barrier functions was associated with viral and bacterial translocation across the epithelial monolayers. Collectively, our data shows that mucosal epithelial cells respond directly to envelope glycoprotein of HIV-1 by upregulating inflammatory cytokines that lead to impairment of barrier functions. The increased permeability could be responsible for small but significant crossing of mucosal epithelium by virus and bacteria present in the lumen of mucosa. This mechanism could be particularly relevant to mucosal transmission of HIV-1 as well as immune activation seen in HIV-1 infected individuals.

Human Alpha-Defensin HNP1 Increases HIV Traversal of the Epithelial Barrier: A Potential Role in STI-Mediated Enhancement of HIV Transmission

“…The discrepancy between FITC-dextran diffusion and HIV traversal could be due to the different incubation time in these two assays (1 h vs. 24-48 h, respectively). Additionally, because HIV is known to reduce TERs and disrupt tight junctions (25,32), HNP1 treatment may facilitate HIV-mediated tight junction disruption, leading to an increase in HIV traversal. The intestinal epithelial cells recovered over time, as indicated by an increase in TER values.…”

Visceral leishmaniasis as an independent cause of high immune activation, T‐cell senescence, and lack of immune recovery in virologically suppressed HIV‐1‐coinfected patients

“…In addition, it has been shown that HIV-1 infection inhibits the intracellular killing of Leishmania, interfering with parasite clearance [14][15][16]. It has also been postulated that gut parasitization by Leishmania amastigotes accelerates the mucosal damage associated with HIV-1 infection, increasing the levels of microbial translocation into the bloodstream, causing a systemic proinflammatory response and increasing immune activation [17][18][19][20][21][22][23][24]. Furthermore, higher T-helper type 2 (Th2) cytokine production has been observed in peripheral blood mononuclear cells (PBMCs) from coinfected patients [12,25].…”

Stable CD4 Expression and Local Immune Activation in the Ectocervical Mucosa of HIV-Infected Women

“…Increased levels of genital tract proinflammatory cytokines can promote viral replication in the mucosa and thereby recruit immune target cells leading to increased HIV shedding (19)(20)(21). When an HIV-infected sexual partner is involved, HIV particles in the seminal fluid and the fluid itself may also cause genital epithelial damage and further inflammation (22,23). This immune activation can result in influx of HIV target cells and upregulation of CD4, CCR5, and CLR expression on selected cell populations in the genital tissue.…”