Isoforms of the E2 molecule: D44 monoclonal antibody defines an epitope on E2 and reacts differentially with T cell subsets

Abstract Human T cell rosetting with erythrocytes is clearly dependent on the CD2‐CD58 interaction. We have previously demonstrated that other T cell molecules are involved in the rosette phenomenon, including the E2 molecule, a 32‐kDa transmembrane glycoprotein. In this report we show that the D44 monoclonal antibody (mAb), previously shown to subdivide T cells into subpopulations with distinct functional repertoires and to identify 70% of lymphocytes from bronchoalveolar lavage from HIV + patients, defined a new epitope on the E2 molecule. This was illustrated by the reactivity of the D44 mAb in Western blot experiments performed with the immunoaffinity purified E2 molecule. Moreover, double‐labeling experiments showed that the E2 molecule exhibited varying epitopes when expressed in different cell types. The D44 and 12E7 epitopes were restricted to distinct subpopulations of T cells and, more importantly, the D44 expression was limited to the CD29 + population including the memory subset. The O662 and L129 epitopes are present on all T cells. Thus, the E2 molecule has both common and variable epitopes in its extracellular domain, and only the common epitopes seem to be involved in T cell adhesion processes.