Varying roles of E-selectin and P-selectin in different microvascular beds in response to antigen

Expression of E-selectin and P-selectin is critical in the effector phase of leukocyte recruitment in response to Ag. Whether their relative roles differ between tissues in response to the same Ag is unknown. In this study, a type I hypersensitivity response was elicited in C57BL/6 mice by systemic sensitization with OVA. Following local Ag challenge, endothelial selectin expression was examined in the skin and cremaster muscle microvasculature using a dual-radiolabeled mAb technique. Next, the dermal and muscle microcirculations were visualized using intravital microscopy to establish roles for P-selectin and/or E-selectin. In untreated mice, leukocyte recruitment in both skin and skeletal muscle was mediated entirely by P-selectin. Following Ag challenge, leukocyte rolling flux and adhesion were dramatically increased and leukocyte rolling velocity was unchanged in muscle. Only P-selectin expression increased in muscle, and leukocyte recruitment was entirely dependent upon this selectin. In contrast, in Ag-challenged skin, leukocyte rolling flux did not increase, but rolling velocity dropped profoundly. In skin, only E-selectin expression increased, and blockade of either E-selectin or P-selectin had minimal effect on either rolling flux or rolling velocity. Blockade of both selectins reduced rolling flux by 80% and increased rolling velocity sevenfold. These data highlight striking differences in expression of the endothelial selectins in separate microvascular beds in response to the same stimulus and demonstrate that these differences underlie very different patterns of leukocyte recruitment. The data underscore the importance of studying individual microvascular beds to understand tissue-specific leukocyte recruitment in vivo.