The rabbit immune system: cells regulating the proliferative response of purified T cells to concanavalin A and phytohaemagglutinin.

T cell specific, B cell specific and Ia specific polyclonal antisera, as well as monoclonal antibodies, were employed to characterize cells involved in regulation of T cells, proliferating upon stimulation with concanavalin A or phytohaemagglutinin. Evidence for Ia+ accessory cells was obtained and the constellation of membrane antigens was determined by cytotoxic cell kill with the above mentioned antibodies. Help given by Ia+ cells was not blocked by polyclonal antibody against Ia, in the absence of complement. There was indirect evidence that a fraction of helper/accessory cells were Ia-.