Epithelial barrier protection : implications for HIV susceptibility

Abstract

The majority of HIV infections today occur through sexual HIV transmission. The female genital mucosa offers a barrier against incoming pathogens. Although, studies show that the vaginal microbiome, co-current infections and local inflammation, the use of hormonal contraceptives and microbicides, can weaken this protective lining. In this thesis in situ digital image analysis workflows were developed and used together with protein profiling, to characterize the effects of such factors on the genital mucosal barrier integrity and the immune cells therein.

Topically applied microbicides can protect against HIV. In paper I we introduced image analysis as a refined tool for evaluation of microbicide safety. We confirmed that a promising microbicide candidate, Q-GRFT, had no negative effect on the rectal epithelium while causing a small, but probably biologically negligible, increase in CD4+ HIV target cells. We also discovered potential effects of multiple biopsy sampling that should be considered when designing pre-clinical studies. Specific tissue resident immune cells with an effector memory phenotype have a rapid response against re-infections and may be important against HIV infection. In paper II, we observed that HIV infected women had increased levels of CD103-CD8+ tissue resident memory cells compared to uninfected women, and that this may be due to a recent influx of these effector cells that have not yet upregulated the CD103 retention molecule. In paper III we revealed that women taking the hormonal contraceptive DMPA, had a thinner superficial layer of the female genital mucosa. Lack of this protective layer in combination with having more HIV target cells located closer to the vaginal lumen, could contribute to the increased HIV risk in women taking DMPA. In paper IV we discovered that Lactobacillus non-iners dominated women had a more intact epithelium, and Gardnerella dominated women had a different spatial localization of CD4+ cells in the epithelium. Secreted protein profiles from Lactobacillus dominant women had elevated levels of anti-inflammatory and epithelial barrier proteins compared to non-Lactobacillus dominant women. These factors may contribute to reduced HIV risk in Lactobacillus-dominant women.

The results of this thesis highlight the benefits of using digital image analysis as a tool for studying spatial and structural changes in the mucosal tissue barrier and the immune cell landscape therein. We showed potential mechanisms in how different factors increase the HIV risk. These findings will support development of interventions aimed to strengthen the mucosal barrier, and thereby reduce transmission of sexually transmitted infections.