ABSTRACT:Spleen cells obtained 30 days after the first immunization of rats isoimmunized with an extract of male accessory glands (MAG) were capable of adoptively transferring specific cell‐mediated immunity to normal syngenic recipients. Humoral and cell‐mediated immune responses were investigated in donor and in the recipient rats that were killed 7 days after intravenous (IV) injection of the cells. In recipient rats the cell‐mediated immunity showed multiple ways of expression and in some cases this was exemplified by a sharp increase in regard to the donor's response. Furthermore, a widespread reactivity in the spleen, lymph nodes, and thymus cells was detected. On the contrary, no circulating antibodies to MAG antigens were demonstrated after the spleen cell transfer. Cell separation studies showed that a nylon woolnonadherent cell was responsible for the transfer of the cell‐mediated immune response. This was abrogated by depletion of T lymphocytes and treatment with antirat thymocytes serum and complement. The mechanism of transfer and development of the cell‐mediated immunity in recipient rats is