COENGAGEMENT OF CD2 WITH LFA-1 OR VLA-4 BY BISPECIFIC LIGAND FUSION PROTEINS PRIMES T-CELLS TO RESPOND MORE EFFECTIVELY TO T-CELL RECEPTOR-DEPENDENT SIGNALS

To examine the effects of ligand engagement and accessory molecule jux taposition on T cell receptor (TCR) signaling, we prepared LFA-3/ICAM- 1 Rg and LFA-3/VCAM-1 Rg bispecific immunoglobulin fusion proteins (Rg , recombinant globulin). These novel fusion proteins allowed us to exa mine the effects of ligand driven co-engagement of T cell proteins CD2 and LFA-1 or CD2 and VLA-4 on TCR-dependent mobilization of intracell ular Ca2+. We observed that preincubation of resting T cells with LFA- 3/ICAM-1. Rg or LFA-3/VCAM-1 Rg fusion proteins resulted in significan tly enhanced mobilization of intracellular Ca2+ following TCR-accessor y molecule cross-linking relative to T cells preincubated with each of the monospecific Rgs alone or with combinations of the monospecific R g fusion proteins. In addition, such coengagement stimulated TCR-depen dent activation and tyrosine phosphorylation of phospholipase C gamma 1 (PLC gamma 1) These results suggest that when T cells interact with antigen presenting cells the engagement of multiple cell adhesion mole cules such as CD2, LFA-1, and VLA-4 primes the T cell to respond more effectively to signals delivered through the TCR.