Analysis of human peripheral blood T lymphocytes proliferating in response to sensitizing antigens: effect of interleukin-2 (IL-2)-responsive bystander cells.

The contribution of interleukin-2 (IL-2)-responsive bystander cells to the proliferative responses of human peripheral blood T lymphocytes to antigens used for sensitization such as Purified Protein Derivative (PPD), Tetanus toxoid (T T) and Influenza virus was investigated. Marked proliferation of the unfractionated peripheral blood mononuclear cells (PBMC) was observed following stimulation with these antigens to which the individuals were known to have been sensitized previously. Depletion of large granular lymphocytes (LGL) from PBMC resulted in substantial reduction in the response of the lymphoid cells in proliferating to the antigens. Proliferation of the T4+T8- (helper)-enriched population, or T4+T8- subset depleted of any IL-2 receptor (IL-2R)-bearing lymphoid cells to these antigens was comparable to that of LGL-depleted PBMC cultures. Cell titration experiments of the blast cells generated from these cultures revealed that PBMC-derived population contained fewer antigen-reactive lymphocytes. These results, therefore, suggested that IL-2-responsive LGL through expansion affected the concentration of antigen-proliferating T cells in the antigen-stimulated PBMC cultures.