MONOCLONAL-ANTIBODIES TARGETING MURINE LFA-1 INDUCE LFA-1/ICAM-1-INDEPENDENT HOMOTYPIC LYMPHOCYTE AGGREGATION

We have identified three anti-murine LFA-1 α monoclonal antibodies ( M17 4.2, G-48, and FD441.8) which are capable of inducing homotypic aggregation of murine T cell lines (3A91 EL-4 cells). The LFA-1 -induced aggregation is temperature-dependent, necessitates metabolic energy, and requires an intact cytoskeleton, but is independent of transcription and protein synthesis. The aggregation is inhibited in Ca2+ and Mg2+ free media and is also blocked with EDTA and EGTA. The aggregation does not involve protein kinase A or C or changes in intracellular calcium. The LFA-1α-induced homotypic aggregation is inhibited with LFA-1β antibodies, but not with antibodies targeting ICAM-1, VCAM-1, VLA-4, or CD2. 3A9 cells do not express the LFA-1 ligand ICAM-1, whereas EL-4 cells express moderate amounts of ICAM-1. Thus, targeting LFA-1α with mAb results in homotypic aggregation of T cell lines which is independent of ICAM-1 LFA-1 interactions, but may involve other LFA-1 ligands such as ICAM-2 or ICAM-3. Alternatively, LFA-1 may function as a signaling molecule, triggering other yet to be defined adhesion molecules to interact. © 1992.