T cell help in human antigen‐specific antibody responses can be replaced by interleukin 2

Abstract

Recombinant IL2, and immunosorbent/high performance liquid chromatography‐purified interleukin 2 (IL2) obtained from the human T cell leukemic line Jurkat, but not interferon‐α or ‐γ, were able to substitute for T cells in specific antibody responses to influenza virus by T cell‐depleted (E⁻) human peripheral blood mononuclear cells, and resulted in antibody formation equivalent to that obtained in the presence of T cells. The antibody response was shown to be antigen specific by using two non‐cross‐reacting strains of influenza virus (A/X31 and B/HK). IL2 in this assay therefore functions as a T cell‐replacing factor. Less than 1 % of T (UCHT1⁺) cells were present in the E⁻ preparations, and this number did not increase during the 7‐day culture with antigen and IL2. Because the frequency of T helper cells for X31 is known to be less than 5 ± 10⁻⁵, this low number of contaminating cells excluded indirect action of IL2 through antigen‐specific T helper cells. Three to four times less IL2 was required for antibody production by E⁻ cells than was needed for optimal proliferation by an IL2‐ dependent T cell line. Moreover, the concentration of anti‐Tac required for 50% inhibition of the IL 2‐induced antibody response was 50 times less than required for 50% inhibition of IL2‐dependent proliferation by the T cell line. But when T cells were added back to the E⁻ cells, the anti‐Tac inhibition curve shifted back to that obtained with the T cell line. In cell labeling experiments, Leu11⁺ cells but not HNK1⁺ cells were increased in E⁻ cells cultured with antigen and IL2. This increase in Leu 11⁺ cells was abolished by prior passage of the E⁻ cells through Sephadex G‐10 columns without affecting the IL2‐induced antibody response. From these experiments we conclude that IL2 can replace T cells in specific antibody responses, and that the IL 2 effect is not mediated indirectly through T cells or large granular lymphocytes.