Cell adhesion to immobilized SIRP fusion proteins was performed in the presence of different SIRPα/β-reactive MoAbs. The inhibitory capacity of the MoAbs was evaluated using a Zeiss Axiovert microscope (n = 3). Deletion constructs expressing only the N-terminal Ig-like domain (SIRPα1Ig1) or the second and third Ig-like loop (SIRPα1Ig2-3) were overexpressed in 293E cells. FACS analysis with the transfected cells revealed the specificity of the different SIRPα/β-reactive MoAbs for either SIRPα1Ig1 or SIRPα1Ig2-3.

SIRP indicates signal-regulatory protein; MoAb, monoclonal antibody; Ig, immoglobulin; +, inhibition of cell adhesion; −, no inhibition of cell adhesion; nb, no binding of cells; (+), partial inhibition of cell adhesion.