The group used an ex vivo infection model of vaginal epithelial sheets from 11 donors, which were then inoculated with HIV-1 and cultured. Multiple rounds of cell sorting were completed to select for and increase the number of discrete LCs. DNA was then isolated, and a specific type of PCR assay was performed which will only amplify viral DNA if it has been integrated into the host cell genome, as in infection. No viral integration was detected in any of the LC samples, indicating that the cells do not support a productive infection.
Next, the group tested whether these LCs could pass along the virus to T-cells, despite not being productively infected. The LCs were co-cultured with peripheral blood-derived lymphoblasts, and co-cultures were maintained for 28 days. By the end of the assay, all cultures had turned positive by Gag p24 release assay. This indicates that the LCs can pass along the virions to CD4 T-cells, which can then become productively infected. Examination by confocal microscopy showed that a specific subset of vaginal LCs lacks langerin expression, and this may aid HIV-1 in bypassing a langerin-mediated degradation pathway
In summary, the Hladik group has shown that LCs mediate HIV infection by migrating from the epithelium to transmit virus to CD4+ T-cells. Productive infection of LCs is not necessary for them to transmit the virus, and in fact may aid HIV in avoiding antiviral innate immune responses. In addition, the LCs containing HIV move away from the mucosa where topical antiviral drugs are used, so this potential mechanism of viral evasion must be considered in clinical use of the microbicide products.
Ballweber L, Robinson B, Kreger A, Fialkow M, Lentz G, McElrath MJ, Hladik, F. 2011. Vaginal Langerhans cells non-productively transporting HIV-1 mediate infection of T cells. Journal of Virology. doi: 10.1128/JVI.05615-11