Journal of Leukocyte Biology 49:329-341 (1991) © 1991 Wiley-Liss, Inc. Function and Regulation of the Murine Lymphocyte CD2 Receptor

The CD2 receptor on T-Iymphocytes plays a major part in mediating adhesive interactions via the LFA-3 Ilgand and in transducing signals for lymphocyte activation. In this study the expression, function, and internalization of the CD2 receptor was investigated in resting and activated murine T-cells. Surface Iodination of intact lymphocytes showed that both types of cell expressed this antigen as a single polypeptide of 63 KDa, and flow cytometry analysis demonstrated that there was four times as much CD2 on Iymphoblasts as on resting cells. Moreover, the CD2 receptor had a more prominent role In the adhesion of the activated lymphocytes to extravascular cells than in the binding of resting cells. Only activated lymphocytes Internalized CD2, in the presence or absence of the anti-CD2 monoclonal antibody (mAb) 12-15, more than 80 % of the 12-15/CD2 complex being removed from the cell surface within 24 hr. Application of 125l-labelled mAb 12-15 followed by subcellular fractionation on Percoll gradients showed that the complex was internal-ized Initially Into a low-density compartment and subsequently transported to heavy-density organdIes, in which it was degraded. Immunogold electron microscopy revealed that immediately after the initial binding of mAb 12-15 to the lymphoblasts, the gol