Helper T cells recognize foreign antigens provided these are presented by inducer cells (such as macrophages and B lymphocytes) bearing class II histocompatibility antigens. The helper T cell carries T-cell receptors, which recognize the class II antigens on the inducer cell. Interleukin-I released by inducer cells stimulates helper T cells to release interleukin-2, which in turn triggers the release of other cytokines. Consequently there is a proliferation of B lymphocytes and the generation of effector T cells, i.e. cytotoxic T cells, delayed hypersensitivity T cells and suppressor T cells.