Absence of L-selectin delays mucosal B cell responses in nonintestinal effector tissues

Previous studies suggest that lymphocyte trafficking to head and neck lymph nodes, also referred to as cranial-, oral-, nasal-associated lymphoid tissue (CONALT), is L-selectin (L-Sel) dependent, despite coexpression of alpha(4)beta(7), resulting in their marked reduction in L-Sel-deficient (L-Sel(-/-)) mice. Consequently, early phase (16 days) Ab responses to cholera toxin (CT) are diminished. The following studies reveal that lack of mucosal effector responses is not caused by loss of inductive immune responses in the L-Sel(-/-) CONALT. Indeed, there was an increased accumulation of total IgA, but not Ag-specific IgA Ab-forming cells (AFC) in L-Sel(-/-) CONALT. This increased accumulation was not evident in L-Sel(+/+) CONALT. Identification of lymphocyte-homing receptors on L-Sel(-/-) and L-Sel(+/+) CONALT lymphocytes revealed no significant differences in expression of alpha(4)beta(7), which might contribute to lymphocyte homing in the absence of L-Sel. Studies of CONALT responses during the late phase (6 wk post-intranasal immunization) revealed the number of lymphocytes recovered from L-Sel(-/-) CONALT was less than L-Sel(+/+) CONALT; however, L-Sel(-/-) CT-specific and total AFC did not vary from 16-day responses, suggesting a defect in CT-specific B cell export. No significant differences in alpha(4)beta(7) expression between L-Sel(-/-) and L-Sel(+/+) CONALT were noted. Yet, these increases in CONALT AFC correlated with restoration of immunity in L-Sel(-/-) nasal passages and reproductive tracts.