Surface expression and synthesis of I-A and I-E/C encoded molecules by B lymphocytes and Ig-secreting cells

Splenocytes from recombinant mice were radiolabeled before or after deletion of subpopulations by cytotoxic anterisera (+C) directed against I-A, I-E/C, IgM, or Ig. Examination of the lysates of the surviving cells by immunoprecipitation demonstrated that 1) virtually all I-A and I-E/C molecules are co-expressed and synthesized by Ig⁺, IgM⁺ lymphocytes, 2) I-A, I-E/C, and IgM molecules are present on many of the cells secreting IgM and IgG, and 3) populations of bearing or Ig secreting cells that lack detectable I-A and I-E/C antigens can be identified in spleen cell populations. The co expression of I-A and I-E/C on most cells of the B cell lineage is discussed in terms of our present concepts of Ir gene control of immune responses.