Cutting edge:: Dichotomy of homing receptor dependence by mucosal effector B cells:: αE versus L-selectin

The common mucosal immune system may be compartmentalized because lymphocyte homing to the upper respiratory tract appears to be mediated by L-selectin interactions rather than alpha (4)beta (7) interactions, as is the case for gut-associated lymphoreticular tissue. To assess the role of L-selectin in effector B cell immunity, L-selectin-deficient mice were intranasally immunized with cholera toxin (CT), and mucosal immune responses were compared with C57BL/6 mice. The absence of L-selectin correlated with a reduction in CT-specific secretory-IgA responses in nasal passages and reproductive tract, but not intestinal lamina propria. Cell sorting experiments showed that an L-selectin-dependent subset was responsible for CT-specific responses in nasal passages and reproductive tract, whereas an alpha (E)beta (+)(7) B cell subset was responsible for L-selectin-independent intestinal immunity. This study provides evidence for compartmentalization of the common mucosal immune system into "intestinal" vs "nonintestinal" effector sites.