Expression of individual Ia specificities on T and B lymphocytes

Ia antigens are coded by genes mapping in the I region of the H 2 gene complex. Individual Ia specificities have been identified which are controlled by different I sub regions. Tissue distribution studies with multispecific anti Ia sera suggested expression of these antigens on both T and B lymphocytes. Since some of the Ia antigens could be associated with the Ir gene product, it was important to determine expression of individual Ia specificities on T or B lymphocytes. Several anti Ia sera were tested by both direct tests and absorptions against lymphocytes from nude mice and anti Thy.1 treated spleen and lymph node lymphocytes as B cell populations, and against cortisone resistant thymocytes and T cell tumors as T cell populations. Ia.6 was found to be expressed exclusively on T cells. Antisera defining specificities Ia.1, 7, 9, 11, 12, 13 and 15 are reactive with both T cells and B cells. Ia,2, 3, 4, 5, 8, 10, and 14 were found on B cells, but their presence on T cells was inconclusive. Extensive absorptions were carried out with tumor cell line S1, and H 2(d) Thy 1 positive tumor. Antiserum (B10 x HTI) anti B10.A(5R) [anti Ia.7] contains two antibody populations, one reacting with T cells, the other with B cells. Absorption with S1 tumor cells left reactivity for lymphocytes of H 2(d) nude mice and vice versa. Screening of 20 anti Ia sera revealed wide variations in their T cell activity. Some had no activity against T cells.