ANTI-CD53 MONOCLONAL-ANTIBODY INDUCED LFA-1 ICAM-1-DEPENDENT AND LFA-1/ICAM-1-INDEPENDENT LYMPHOCYTE HOMOTYPIC CELL-AGGREGATION/

CD53 is a pan-leukocyte glycoprotein and belongs to a member of the te traspan family of cell membrane proteins. The predicted structure and functional characteristics of CD53 suggest that it may play important roles in transmembrane signaling, but its roles in cell adhesion have not been clarified. The present study shows that anti-CD53 monoclonal antibody (mAb), HI29 induced homotypic cell aggregation of lymphoid ce ll lines including a B cell line from a patient with leukocyte adhesio n deficiency syndrome (LAD). The homotypic cell aggregation was blocke d by another anti-CD53 mAb, MEM53, in all the examined cell lines and by anti-LFA-1 (CD11a/CD18) or anti-ICAM-1 (CD54) mAbs in the cell line s except for the LAB line, but it was not blocked by anti-CD44 or anti -CD49d mAb. The induced homotypic cell aggregation was energy-dependen t. These findings suggest that CD53 relates to LFA-1/ICAM-1-dependent and -independent pathways of homotypic cell aggregation of lymphocytes and that it plays an important role in lymphocyte activation and cell adhesion.