In vitro priming of human lymphocytes. I. IL-2 and IL-4 requirements

Abstract

Induction of antigen-dependent IgM and IgG responses by human in vitro spleen cell cultures were supported by addition of defined lymphokines. Whereas exposure to IL-2 alone throughout both immunization and cultivation period supported the highest antigen-directed responses, antibodies of higher relative affinity to the immunizing antigen were secreted under conditions of shorter IL-2 exposure. Continuous presence of IL-2 supported the antigen-driven responses for up to 15 days, the later part of which was characterized by a very low relative affinity index value. IL-2 supported cultures produced up to 55 times and 36 times more IgM and IgG, respectively, than cultures without added IL-2. Addition of IL-2-neutralizing antibodies throughout the cultivation period abrogated all responses. Addition of IL-4 alone had negligible effect on the antigen-directed IgM responses but supported antigen-independent IgG responses. Neutralization of IL-4 alone had negligible effect on the IgM and IgG responses, whereas neutralization of IL-4 during IL-2 support, resulted in reduction of antigen dependency of responses.

Delayed IL-4 neutralization (24 hours) restored some of the antigen sensitivity. IL-4 reduced IL-2-induced, antigen-directed immunoglobulin responses but supported increased antigen-induced, antigen-directed responses, resulting in maximal antigen-specific responses. IL-4 reduced the IL-2-induced immunoglobulin production. IL-2 supported cell division, whereas IL-4 supported prolonged survival. Flow cytometry tests showed that IL-2 primarily induced CD8⁺ cells (T_{suppressor/cytotoxic}) and OKT-10⁺ cells (plasma cells) cells, whereas the number of B1⁺ cells (B cells) decreased. IL-4 induced slight increases in the amount of B1⁺ cells and CD4⁺ cells (T_helper).