Reevaluation of P-Selectin and α4 Integrin as Targets for the Treatment of Experimental Autoimmune Encephalomyelitis

Abstract

There has been a great deal of interest in adhesion molecules as targets for the treatment of multiple sclerosis and other inflammatory diseases. In this study, we systematically evaluate α4 integrin and P-selectin as targets for therapy in murine models of multiple sclerosis–for the first time directly measuring the ability of their blockade to inhibit recruitment and relate this to clinical efficacy. Experimental autoimmune encephalomyelitis was induced in C57BL/6 or SJL/J mice and intravital microscopy was used to quantify leukocyte interactions within the CNS microvasculature. In both strains, pretreatment with blocking Abs to either α4 integrin or P-selectin reduced firm adhesion to a similar extent, but did not block it completely. The combination of the Abs was more effective than either Ab alone, although the degree of improvement was more evident in SJL/J mice. Similarly, dual blockade was much more effective at preventing the subsequent accumulation of fluorescently labeled leukocytes in the tissue in both strains. Despite evidence of blockade of leukocyte recruitment mechanisms, no clinical benefit was observed with anti-adhesion molecule treatments or genetic deletion of P-selectin in the C57BL/6 model, or in a pertussis toxin-modified model in SJL/J mice. In contrast, Abs to α4 integrin resulted in a significant delay in the onset of clinical signs of disease in the standard SJL/J model. Despite evidence of a similar ability to block firm adhesion, Abs to P-selectin had no effect. Importantly, combined blockade of both adhesion molecules resulted in significantly better clinical outcome than anti-α4 integrin alone.

E- and P-Selectin Are Not Required for the Development of Experimental Autoimmune Encephalomyelitis in C57BL/6 and SJL Mice

“…Our observations are, however, in accordance with previous findings made by us and others, demonstrating that targeting of either E-or P-selectin (alone or both together) or their common ligand PSGL-1 by blocking Abs does not influence inflammatory cell recruitment into the CNS and the development of EAE in the SJL or the C57BL/6 mouse model (9,16,18). Additionally, three independent studies demonstrated that PSGL-1-deficient C57BL/6 mice develop MOG aa35-55 -induced EAE indistinguishable from wild-type C57BL/6 mice (9,18,19). Similarly, P-selectin-deficient C57BL/6 mice develop MOG aa35-55 -induced EAE just like wild-type mice (9).…”

“…Other studies have, however, failed to detect the expression of E-and P-selectin in CNS microvessels during EAE (16) or shown that cultured brain microvascular endothelial cells lack storage of Pselectin in Weibel-Palade bodies (17). Also, in apparent contrast to the observation of E-and P-selectin-mediated leukocyte rolling in superficial brain microvessels by intravital microscopy, Ab inhibition studies blocking E-and P-selectin or PSGL-1 failed to inhibit the development of EAE in the SJL mouse model (9,16,18). Furthermore, several studies have now demonstrated that C57BL/6 mice deficient for PSGL-1 or P-selectin develop MOG aa35-55 -induced EAE indistinguishable from C57BL/6 wild-type mice (9,18,19).…”

“…In accordance with our present findings detecting Pselectin but not E-selectin in inflamed CNS microvessels during EAE, P-selectin-, but not E-selectin-, mediated rolling of endogenous leukocytes was observed in superficial brain vessels of C57BL/6 mice suffering from EAE (8). The important role of Pselectin in mediating leukocyte rolling in this vascular compartment during EAE has been further supported by the recent observation that leukocyte rolling is completely abrogated in superficial brain vessels of P-selectin-deficient mice (9).…”

“…Using intravital microscopy, we have demonstrated that the recruitment of encephalitogenic T cell blasts across the spinal cord white matter microvasculature in healthy mice depends on ␣ 4 integrin-mediated initial capture and G protein-dependent arrest (7). In inflamed pial venules of mice suffering from EAE, ␣ 4 integrins contribute to rolling and mediate G protein-dependent arrest of endogenous leukocytes (8,9) or encephalitogenic T cells (10). Thus, ␣ 4 integrins can mediate both the initial low-affinity interaction of circulating leukocytes with the CNS microvasculature and the subsequent G protein-dependent arrest requiring high-affinity binding of ␣ 4 integrins.…”

“…Despite the predominant involvement of ␣ 4 integrins in leukocyte interaction with the BBB, a number of studies using intravital microscopy of the brain have convincingly demonstrated that Eand P-selectin are expressed in superficial blood vessels of the brain (10) and by interaction with P-selectin glycoprotein ligand (PSGL)-1 mediate the tethering and rolling of endogenous leukocytes or T cells in these vessels in nicotine (14), TNF-␣, or LPStreated mice (15) or in mice suffering from EAE (8,9). Other studies have, however, failed to detect the expression of E-and P-selectin in CNS microvessels during EAE (16) or shown that cultured brain microvascular endothelial cells lack storage of Pselectin in Weibel-Palade bodies (17).…”