Neutrophils migrate to delayed-type hypersensitivity reactions in joints, but not in skin. Mechanism is leukocyte function-associated antigen-1-/Mac-1-independent.

We have previously found that polymorphonuclear leukocyte (PMNL) migration to adjuvant arthritic joints of rats was only partially inhibited by mAbs to the adhesion molecules LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18), suggesting that there is a CD11/CD18-independent mechanism for PMNL migration to inflamed joints. Adjuvant arthritis in rats is believed to be initiated by a T lymphocyte-dependent immune response and maintained by proinflammatory cytokines such as IL-1 and TNF-alpha. Here we studied two types of joint inflammation: that induced by a delayed-type hypersensitivity (DTH) reaction in the joint and that induced by intra-articular (i.a.) injection of cytokines, to explore PMNL migration to inflamed joints and examine the role of CD18. 51Cr-labeled blood PMNL were used to measure PMNL migration in rats to inflammatory reactions in joints and compared with reactions in skin. A large number of PMNL migrated to the carpal and talar joints after i.a. injection of Mycobacterium purified protein derivative in sensitized animals to induce DTH, but there was minimal PMNL migration to this DTH reaction in the skin. This migration to the joints was not inhibited by mAbs to LFA-1 alone or mAbs to LFA-1 plus Mac-1 that almost completely inhibited PMNL accumulation in dermal inflammatory reactions induced by zymosan-activated serum (C5adesArg), endotoxin, IL-1 alpha, or TNF-alpha in the same rats. Intra-articular injection of the cytokines IL-1 alpha and TNF-alpha, but not IFN-gamma, induced marked PMNL accumulation in the joints; this was strongly inhibited by the treatment of rats with anti-LFA-1 and anti-Mac-1. Thus, PMNL migrate to DTH induced in joints but not in skin, and this migration is CD18-independent, but migration to i.a. IL-1 alpha and TNF-alpha is largely CD18 dependent in both joints and skin. This suggests that both the joint microenvironment and the T cell dependence of the inflammatory reaction in the joint governs the mechanism of PMNL recruitment.