Identification of mouse thymus antigen recognition function in a minor, low-density, low-theta cell subpopulation

Using a one- or two-step syngeneic transfer system in bone marrow-restored, lethally irradiated mice, the anti-SRBC cooperative cell function of the thymus was identified as being in low-density cell subpopulations constituting less than 10% of total thymus cells. This “B layer” population consisted of about 30% small lymphocytes and 70% large lymphoid cells and blasts, which have an average Θ-antigen content more characteristic of peripheral lymphocytes than of thymocytes. The origin of these cells and some possible implications of these findings are discussed.