Characterization of a novel rat thymocyte costimulating antigen by the monoclonal antibody 1.3.

Abstract

To define membrane-associated molecules that impart signals for the activation and expansion of double negative (DN) cells, mAb were raised against in vitro-cultured rat DN cells. One such mAb, 1.3, stimulated proliferation of DN cells along with submitogenic concentrations of PMA and IL-2 without affecting the mobilization of Ca2+. The 1.3 mAb precipitated a heterodimeric protein from DN cells and kidney (130/110 kDa). Although the tissue distribution and biochemical characteristics of the 1.3 determinant resemble the neutral aminopeptidase (AP-N) first described as the thymocyte activating molecule in the mouse, other data are contradictory; AP-N message was not detected in mRNA from 1.3 positive cells and the AP-N gene was absent in the genomic DNA from rat DN hybridomas expressing high levels of 1.3 Ag. In addition, the 1.3 mAb did not affect AP-N enzyme activity suggesting that 1.3 mAb does not function through this enzyme to transduce signals for proliferation. Thus, the 1.3 mAb defines a new and important thymocyte costimulating Ag.