Analysis of responder cell-cell interactions in the syngeneic mixed leukocyte response

In a previous study we identified the target antigens on stimulator cells in the murine syngeneic mixed leukocyte response (MLR) as self Ia molecules. The experiments reported here utilized analysis of log-log cell number-response titration slopes to study the responder T-cell population in the syngeneic MLR. The data indicated that in the peripheral lymphoid population at least two cell populations interact to produce a murine syngeneic MLR. One of these cell types appeared to be a member of an Lyt 2- subset, another a member of an Lyt 2+ subset. A potential third cell type, which was detected in the presence of (PMA)-induced EL4 supernatants, was found in the thymus, an organ that did not appear to contain either of the other two subsets. Experiments with adult thymectomized and neonatal mice suggested that the cell populations involved in the syngeneic MLR were mature T cells and were not an early differentiation state of T lymphocytes whose ability to be stimulated by Ia antigens alone was a transient event.