Both CD8+ and CD16+ human T cell clones can provide B cell help for immunoglobulin production

Summary The functional properties of two CD4⁺CD8⁻CD16⁻, five CD4⁻CD8⁺CD16⁻ and three CD4⁻CD8⁻CD16⁺ human T cell clones were compared. All CD4⁻ T cell clones displayed strong cytolytic activity in the lectin-dependent lytic assay against the P815 murine mastocytoma cell line, but only the CD4⁻CD8⁻CD16⁺ T cell clones exhibited lytic activity against the natural killer-sensitive K562 cell line. Upon activation with anti-CD3 monoclonal antibody, all T cell clones were able to support IgM and IgA synthesis in autologous B cells. Both CD4⁺ and CD4⁻ T cell clones required cell-to-cell interaction with the B cells in order to exert their helper activity for immunoglobulin production. However, unlike CD4⁺, CD4⁻CD8⁺CD16⁻ and CD4⁻CD8⁻CD16⁺ T cell clones provided helper function for immunoglobulin synthesis only when low T/B cell ratios were used in culture. At higher T/B cell ratios, there was a decline in the B cell helper activity of CD4⁻ T cell clones that was probably related to the expression of cytolytic capacity against the antigen-presenting B cell. These data support the notion that under certain experimental conditions even cytotoxic T lymphocytes and natural killer cells may provide B cell helper function.