The role of α₄ and LFA-1 integrins in selectin-independent monocyte and neutrophil migration to joints of rats with adjuvant arthritis

Monocytes and neutrophils are chronically recruited to joints in rheumatoid arthritis. In the joints of rats with adjuvant arthritis, this is mediated, in part, by selectin-dependent and selectin-independent mechanisms. To define the selectin-independent mechanisms, ⁵¹Cr-labeled blood monocytes, ¹¹¹In-labeled neutrophils and function blocking mAb to the selectins and integrins were utilized. Integrins contributed to the selectin-independent monocyte migration to arthritic joints with 58-70% inhibition of this recruitment by anti-α₄ or anti-LFA-1 mAb, relative to selectin blockade alone. α₄ plus P-selectin blockade was as effective as combined blockade of α₄, P-, E- and L-selectin, mediating ~ 83% of the overall monocyte migration to the joints. In contrast, LFA-1 was the predominant selectin-independent mechanism for neutrophil recruitment to the joints. LFA-1 together with P-selectin had essential roles in the talar joint. In dermal inflammation in the arthritic rats, LFA-1 accounted for most (69%) of the selectin-independent monocyte migration to the chemoattractant C5a(desArg) (zymosan-activated serum), whereas LFA-1 and Mac-1 both contributed to selectin-independent neutrophil recruitment to C5a(desArg). α₄ integrin and P-selectin in concert mediated monocyte recruitment to lipopolysaccharide and IFN-γ lesions (81%). Thus: (1) either α₄ or LFA-1 can mediate monocyte migration to arthritic joints in the absence of selectin function and α₄ together with P-selectin is particularly important; (2) LFA-1 is the predominant mechanism of selectin-independent migration of neutrophils to inflamed joints; and (3) in arthritic rats, selectin-independent migration of monocytes and neutrophils to dermal inflammation is mediated by α₄ or LFA-1 or both LFA-1 and Mac-1, depending on the leukocyte type, and inflammatory stimulus.