Lactobacillus species, which dominate vaginal microbiota of healthy reproductive-age women lower the risks of sexually transmitted infections, including the risk of HIV acquisition. The exact mechanisms of this protection remain to be understood. Here, we investigated these mechanisms in the context of human cervico-vaginal and lymphoid tissues ex vivo. We found that all six lactobacilli strains tested in these systems significantly suppressed HIV-1 infection. We identified at least three factors that mediated this suppression. (i) Acidification of the medium. The pH of the undiluted medium conditioned by lactobacilli was between 3.8 and 4.6. Acidification of the culture medium with HCl to this pH in control experiments was sufficient to abrogate HIV-1 replication. However, Lactobacillus-conditioned medium diluted five fold, which reached pH ~ 6.9 was also suppressive for HIV-1 infection while in control experiments HIV-1 infection was not abrogated when the pH of the medium was brought to 6.9 using HCl. This suggested the existence of other factors responsible for HIV-1 inhibition by lactobacilli. (ii) Lactic acid. There was a correlation between the concentration of lactic acid in the Lactobacillus-conditioned medium and its ability to suppress HIV-1 infection in human tissues ex vivo. Addition of lactic acid isomers D and L to tissue culture medium at the concentration that corresponded to their amount released by lactobacilli resulted in HIV-1 inhibition. Isomer L was produced in higher quantities than isomer D and was mostly responsible for HIV-1 inhibition. These results indicate that lactic acid, in particular its L-isomer, inhibit HIV-1 independently of lowering of the pH. (iii) Virucidal effect. Incubation of HIV-1 in Lactobacillus–conditioned medium significantly suppressed viral infectivity for human tissues ex vivo. Finally, lactobacilli adsorb HIV-1 serving as a sink decreasing the amount of free virions. In summary, we found that lactobacilli inhibit HIV-1 replication in human tissue ex vivo by multiple mechanisms. Further studies are needed to evaluate the potential of altering the spectra of vaginal microbiota as effective strategies to enhance vaginal health. Human tissues ex vivo may serve as a test system for these strategies.

The vast majority of new HIV infections in male‐to‐female transmission occurs through semen, where HIV‐1 is present in two different forms: as free and as cell‐associated virus. In the female lower genital tract, semen mixes with female genital secretions that contain various factors, some of which facilitate or inhibit HIV‐1 transmission. Next, HIV‐1 crosses the genital epithelia, reaches the regional lymph nodes, and disseminates through the female host. Cervico‐vaginal mucosa contains multiple barriers, resulting in a low probability of vaginal transmission. However, in some cases, HIV‐1 is able to break these barriers. Although the exact mechanisms of how these barriers function remain unclear, their levels of efficiency against cell‐free and cell‐associated HIV‐1 are different, and both cell‐free and cell‐associated virions seem to use different strategies to overcome these barriers. Understanding the basic mechanisms of HIV‐1 vaginal transmission is required for the development of new antiviral strategies to contain HIV‐1 epidemics.

Objective: Despite lower plasma HIV RNA levels, women progress faster to AIDS than men. The reasons for these differences are not clear but might be a consequence of an elevated inflammatory response in women. Methods: We investigated sex differences in cytokine profiles by measuring the concentrations of 36 cytokines/chemokines by Luminex in blood of women and men (sex at birth) with chronic HIV infection under suppressive therapy. We initially performed a principal component analysis to see if participants clustered by sex, and then fit a partial least squares discriminant analysis (PLS-DA) model where we used cytokines to predict sex at birth. The significance of the difference in nine cytokines with VIP greater than 1 was tested using Wilcoxon test-rank. Further, potential confounding factors were tested by multivariate linear regression models. Results: Overall, we predicted sex at birth in the PLS-DA model with an error rate of approximately 13%. We identified five cytokines, which were significantly higher in women compared with men, namely the pro-inflammatory chemokines CXCL1 (Gro-α), CCL5 (RANTES), CCL3 (MIP-1α), CCL4 (MIP-1β), as well as the T-cell homeostatic factor IL-7. The effect of sex remained significant after adjusting for CD4⁺, age, ethnicity, and race for all cytokines, except for CCL3 and race. Conclusion: The observed sex-based differences in cytokines might contribute to higher immune activation in women compared with men despite suppressive therapy. Increased levels of IL-7 in women suggest that homeostatic proliferation may have a differential contribution to HIV reservoir maintenance in female and male individuals. Our study emphasizes the importance of sex-specific studies of viral pathogenesis.

Vaccinia virus (VACV) has been attracting attention recently not only as a vector for various vaccines but also as an immunization tool against smallpox because of its potential use as a bioterrorism agent. It has become evident that in spite of a long history of studies of VACV, its tissue pathogenesis remains to be fully understood. Here, we investigated the pathogenesis of VACV and its interactions with human immunodeficiency virus type 1 (HIV-1) in the context of human lymphoid tissues. We found that ex vivo-cultured tonsillar tissue supports productive infection by the New York City Board of Health strain, the VACV strain of the Dryvax vaccine. VACV readily infected both T and non-T (B) lymphocytes and depleted cells of both of these subsets equally over a 12-day period postinfection. Among T lymphocytes, CD8 ⁺ cells are preferentially depleted in accordance with their preferential infection: the probability that a CD8 ⁺ T cell will be productively infected is almost six times higher than for a CD4 ⁺ T cell. T cells expressing CCR5 and the activation markers CD25, CD38, and HLA-DR are other major targets for infection by VACV in lymphoid tissue. As a consequence, VACV predominantly inhibits the replication of the R5 _SF162 phenotype of HIV-1 in coinfected tissues, as R5-tropic HIV-1 requires activated CCR5 ⁺ CD4 ⁺ cells for productive infection. Human lymphoid tissue infected ex vivo by VACV can be used to investigate interactions of VACV with other viruses, in particular HIV-1, and to evaluate various VACV vectors for the purpose of recombinant vaccine development.