Effect of integrin beta(2) subunit truncations on LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) assembly, surface expression, and function

LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18) are members of the beta (2) integ rins involved in leukocyte function during immune and inflammatory response s. We aimed to determine a minimized beta (2) subunit that forms functional LFA-1 and Mac-2, Using a series of truncated beta (2) variants, we showed that the subregion Q23-D300 of the beta (2) subunit is sufficient to combin e with the alpha (L) and alpha (M) subunits intracellularly. However, only the beta (2) variants terminating after Q444 promote cell surface expressio n of LFA-1 and Mac-1. Thus, the major cysteine-rich region and the three hi ghly conserved cysteine residues at positions 445, 447, and 449 of the beta (2) subunit are not required for LFA-1 and Mac-1 surface expression, The s urface-expressed LFA-1 variants art constitutively active with respect to I CAM-1 adhesion and these variants express the activation reporter epitope o f the mAb 14. In contrast, surface-expressed Mac-1, both the wild type and variants, require 0.5 mM MnCl2 for adhesion to denatured BSA. These results suggest that the role of the beta (2) subunit in LFA-1- and Mac-1-mediated adhesion may be different.