Induction of antibody responses to influenza virus in human lymphocyte cultures. I. Role of interleukin 2

The in vitro T cell-dependent antibody response of human lymphocytes to influenza virus X31 was used to study the role of T cell-derived lymphokines in antigen-specific responses. Supernatant from cultures of phytohaemagglutinin-stimulated, pooled human tonsil cells (PHA-MLR) was capable of replacing T cells and inducing T-depleted tonsil cells to secrete influenza-specific antibody. The T cell-replacing activity of PHA-MLR supernatant co-purified with interleukin 2 (IL 2) on Ultrogel AcA54 gel filtration and reversed phase-high performance liquid chromatography. PHA-MLR supernatant and IL 2 also enhanced B cell proliferation induced by anti-mu or Staphylococcal aureus strain Cowan I (SAC). A murine monoclonal antibody directed against the human IL 2 receptor (Mab 2A3) was used to completely block the enhancement of influenza-specific antibody production mediated by PHA-MLR supernatant, purified IL 2, and recombinant human IL 2. Mab 2A3 did not affect the T-independent B cell proliferation induced by anti-mu or SAC, but abrogated the enhancing effect of the PHA-MLR supernatant and IL 2 in this culture system. Immunofluorescence studies failed to demonstrate binding of Mab 2A3 to B cells activated by the X31 influenza virus and IL 2, or by SAC. By using Mab 2A3 to mask out IL 2 effects in the influenza-specific culture system, no other B cell differentiating activities were revealed in supernatants from lymphocytic cultures stimulated with a variety of mitogens. Thus, our results indicate that the production of influenza-specific antibodies by T-depleted human lymphocyte cultures is absolutely dependent on the presence of both antigen and IL 2.