Cell-mediated immunity to H-2 antigens. Characteristics of the effector cells as detected in the microcytotoxicity assay.

Cell-mediated immune reactivity against murine histocompatibility antigens was compared by using both the microcytotoxicity assay (MCA) and the 51 chromium release assay (CRA). In both assay systems the data obtained showed T cell-mediated reactivity. In the CRA only T lymphocytes were detectable, which were cytotoxic, In contrast, in the MCA reactivity of nonlytic secondary T cells (NLST) was also detected. NLST acquired their MCA-reactivity within the first 24 hr of the 48-hr test period of the MCA. Circumstantial evidence is provided suggesting that MCA reactivity is a product of two different processes, namely, antigen-specific restimulation of immunt T cells and shedding of cytotoxicity inhibiting factors.