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) integrins involved in leukocyte function during immune and inflammatory responses. 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 combine with the alpha (L) and alpha (M) subunits intracellularly. However, only the beta (2) variants terminating after Q444 promote cell surface expression of LFA-1 and Mac-1. Thus, the major cysteine-rich region and the three highly 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 surface-expressed LFA-1 variants art constitutively active with respect to ICAM-1 adhesion and these variants express the activation reporter epitope of 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.