Selectin-independent leukocyte rolling and adhesion in mice deficient in L-, E-, and P-selectin and ICAM-1

L-, E-, and P-selectin mediate the majority of leukocyte capture and rolling on the inflamed vessel wall. We have recently shown that leukocyte rolling and adherence is drastically reduced in mice lacking L-, E-, and P-selectin (L/E/P-/-) and in mice lacking E- and P-selectin and ICAM-1 (E/P/I-/-). Here, we have generated mice deficient in four adhesion molecules (L-, E-, and P-selectin and ICAM-1) to further investigate selectin-independent mechanisms of leukocyte rolling and adhesion in a TNF-α (0.5 μg, 6 hr) induced model of inflammation of the cremaster muscle. The quadruple knockouts (L/E/P/I-/-) were made by transplanting L-/- bone marrow into lethally irradiated E/P/I-/-. Leukocyte rolling flux was 2 min^-1 in L/E/P/I-/-compared to 77 min^-1 in wild-type mice. Residual leukocyte rolling was completely removed after the administration of an α₄ integrin blocking antibody. Injecting α₄ blocking antibody at the time of TNF-α also reduced leukocyte adhesion (59 mm^-2) compared to L/E/P/I-/- (396 mm^-2) and wild-type (1,080 mm^-2) mice. The only significant accumulation in L/E/P/I-/- occurred at confluent branch points where the fluid flow regime is likely altered. This leukocyte adhesion is selectin-independent and also occurred in mice pretreated with an α₄ integrin blocking antibody. These data show some leukocyte adherence can occur without rolling through selectin and α₄ integrin-independent mechanisms. This recruitment mechanism is confined to venular branch points. Supported by NIH R01 HL54136 to KL.