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HLA class II restriction governing cell cooperation between antigen‐specific helper T lymphocytes, B lymphocytes and monocytes for in vitro antibody production to influenza virus

To study HLA class II compatibility requirement for in vitro antibody production to influenza virus, semipurified T lymphocytes, B lymphocytes and monocytes from HLA‐typed responder donors were used. The presence of the three subpopulations was required for antibody production while a mixture of only two of those was ineffective. When using fresh T lymphocytes which exert an allogeneic suppressive effect and may also exhibit allogeneic helper activity, it was not possible to conclude an HLA class II‐linked restriction of T‐B cell cooperation although there was a suggestion of it. However, a grown H3 hemagglutinin‐specific T cell line (L2), previously shown to be restricted by HLA‐DR molecule (DR1) for interaction with antigen‐presenting cells and devoid of allogeneic reactivity, exerts an HLA class II‐restricted helper activity. This was demonstrated by various combinations of HLA‐DR semi‐compatible or incompatible B lymphocytes and/or monocytes with L2 T cells.