Cultured Langerhans' cells (CLC) exhibit enhanced antigen-presenting function compared to freshly isolated LC (FLC), but they are commonly believed to be inefficient at processing intact proteins. In this study, FLC and CLC from normal, human immunodeficiency virus (HIV) seronegative volunteers were compared for their ability to present the HIV-1 envelope glycoprotein gp120 or reverse transcriptase (p66) antigens to autologous, specific CD4+ T cell lines. Epidermal cell suspensions enriched for LC were prepared from suction blister roofs. FLC stimulated T cells at lower antigen concentrations compared to unfractionated peripheral blood mononuclear cells (PBMC). CLC were more potent on a per cell basis than FLC, PBMC or adherent monocytes at presenting native gp120, native p66 or immunogenic peptides. CLC were also more efficient than FLC or PBMC in terms of the amount of antigen required for T-cell activation. Chloroquine and leupeptin inhibited presentation of intact p66, but not of an immunodominant peptide, by FLC or CLC, thus indicating that both cells utilize antigen-processing mechanisms that are based on intracellular acidification and protease activity. Incubation of CLC with monoclonal antibodies against HLA-DR, CD11b, CD18, CD50, CD54, CD58 or CD80, but not anti-major histocompatibility complex class I (MHC-I), inhibited antigen-specific T-cell proliferation to varying degrees. We conclude that human CLC retain the ability to process and present protein antigens potently to CD4+ T cells. Thus, CLC have the capacity to participate actively in the generation and maintenance of T-helper cell immunity to viral antigens during HIV-1 infection.