HIV-1 infectivity and host range modification by cathepsin D present in human vaginal secretions

Objective: To investigate HIV-1 infectivity in the natural environment of vaginal secretions. Design: Vaginal wash samples collected from 14 healthy women were incubated in vitro with various HIV-1 strains for 10min at 37°C and then assayed for infectivity on primary lymphocyte cultures, or on CEM cells, or on CD4- ME180 cells derived from vaginal epithelium. Methods: HIV-1 infectivity was measured by early virus growth in the various host cells tested using a quantitative p24 assay and by the Kärber procedure. Results: Preincubation of HIV-1IIIB with vaginal wash samples or 2μg/ml cathepsin D increased the ability of the virus to grow in lymphocyte cultures. The vaginal wash effect was abolished by 5μg/ml pepstatin A, an inhibitor of aspartyl proteases. Presence of precursor and mature forms of cathepsin D in vaginal wash was demonstrated after passage through a pepstatin A-agarose column. Median tissue culture infective doses of HIV-1IIIB and HIV-1JRFL strains were increased 14.4-fold and 18-fold, respectively, after preincubation in vaginal wash sample, and were increased by pretreatment with 2μg/ml cathepsin D. When CD4 receptors of CEMss cells were blocked by OKT4a monoclonal antibody, the cells lost susceptibility to HIV-1IIIB, but supported the growth of virus pretreated with vaginal wash sample or cathepsin D. These treated viruses were able to initiate infection of CD4- ME180 epithelial cells, which were not receptive to untreated virus. ME180 cells were shown to possess the messenger of CXC-chemokine receptor-4. Conclusions: Vaginal secretions may help HIV-1 transmission to women by increasing infectivity for CD4+ cells and allowing entrance into some CD4- epithelial cells.