A MONOCLONAL-ANTIBODY, 3 22, TO RABBIT CD11C WHICH INDUCES HOMOTYPIC T-CELL AGGREGATION - EVIDENCE THAT ICAM-1 IS A LIGAND FOR CD11C/CD18/

The rabbit CD11c molecule has been characterized by use of 3 new monoc lonal antibody, mAb 3/22. Expression of the p150.95 integrin (CD11c/CD 18) has been shown by flow cytometry and immunohistochemistry to be re stricted to monocytes, macrophages, dendritic cells and a small popula tion of lymphocytes in peripheral blood. No expression on neutrophils could be demonstrated. Incubation of the newly derived CD8(+) T cell l ine. BJ/873, with mAb 3/22 causes homotypic aggregation, which has bee n shown to be a cell surface event that is not dependent on intracellu lar signaling or on receptor cross-linking. Inhibition studies show th at the ligands responsible for this aggregation are CD11c/CD18 and ICA M-1, both of which are expressed on BJ/873. One other rabbit T cell li ne, K34, that also expresses p150.95 and ICAM-1, shows a similar aggre gation response when stimulated with 3/22. Cell lines that express p15 0.95 but not ICAM-1 do not aggregate. These observations suggest that ICAM-1 is a ligand for activated p150.95.