IMPAIRED ANTIGEN PRESENTATION TO CD4-CELLS BY HIV-INFECTED MONOCYTES IS RELATED TO DOWN-MODULATION OF CD4 EXPRESSION ON HELPER T-CELLS - POSSIBLE INVOLVEMENT OF HIV-INDUCED CELLULAR FACTORS( T)

Defective antigen presentation by HIV-infected monocytes is related to severe immune dysfunction in patients with AIDS, although the mechani sm by which this process occurs is not well defined, Here we report th at reduced capacity by HIV-infected monocytes to stimulate or present antigen to CD4+ T-cells was mediated by cellular factors associated wi th the plasma membranes of HIV-infected monocytes, In contrast, solubl e factors secreted by HIV-infected monocytes had little or no effect o n T-cell stimulation, Reduced T-cell stimulation by HIV-infected monoc ytes was related to down-modulation of CD4 expression on helper T-cell s and was not affected by the inclusion of anti-HIV-gp120 Ab, indicati ng the involvement of soluble or cell-associated viral envelope protei n to be less likely, Exposure of CD4+ T-cells, that had been in co-cul ture with HIV-infected monocytes, to uninfected monocytes partially re stored impaired T-cell stimulation, Thus, for the first time we report that altered capacity of HIV-infected monocytes to stimulate and pres ent antigen to CD4+ T-cells is related to down-modulation of CD4 expre ssion on T-cells, and appears to occur via membrane-associated cellula r factors on HIV-infected monocytes.