Estimation by Radioimmunoassay of VH Determinants (Aa1) Associated with Rabbit T Lymphocytes

A radioimmunoassay with specificity for the a1 allotype determinant of rabbit immunoglobulin (Ig) heavy chains was used for the quantitation of VH in detergent extracts of lymph node cells from a1a1/b4b4 rabbits. B cell-derived Ig in the same extracts was estimated with a radioimmunoassay specific for L-chain. About 2 X 10(5) molecules/cell was found by both assays when assuming a molecular weight of 1.5 X 10(5) dalton. Extracts prepared from lymphocytes depleted of B cells (surface Ig+ cells) were also found to contain corresponding amounts of a1 and L-chain, with values varying from about 10(3) to 10(4) molecules/cellmthe estimates were not influenced by the presence of inhibitors of proteolytic enzymes. Supernatants, obtained after keeping the lymphocytes in culture for 16 h, were analyzed by the same methods. Again, matching amounts of a1 and L-chain were found in supernatants from nonfractionated as well as from B cell-depleted populations. The results obtained indicate that T cells do not carry or produce an excess of a1 compared to L-chain, as would have been expected if the T cell antigen receptor carried the same variable region as the Ig heavy chain while being otherwise composed of nonimmunoglobulin-like structures.