CD1.1 EXPRESSION BY MOUSE ANTIGEN-PRESENTING CELLS AND MARGINAL ZONE B-CELLS

Mouse CD1.1 is an MHC class I-like, non-MHC-encoded, surface glycoprot ein that can be recognized by T cells, in particular NK1.1(+) T cells, a subset of alpha beta T cells with semiinvariant TCRs that promptly releases potent cytokines such as IL-4 and IFN-gamma upon stimulation, To gain insight into the function of CD1.1, a panel of nine mAbs was generated and used to biochemically characterize and monitor the surfa ce expression of CD1.1 an different cell types, CD1.1 is a heavily gly cosylated, beta(2)-microglobulin-associated surface protein, Its recog nition by a panel of 12 V alpha 14-positive and -negative CD1-specific alpha beta T cell hybridomas was blocked by two groups of mAbs that b ound to adjacent clusters of epitopes, indicating that different alpha beta TCRs bind to the same region of CD1.1, presumably above the groo ve, Remarkably, CD1.1 was mainly expressed by dendritic cells, B cells , and macrophages, suggesting a function in Ag presentation to Th cell s. Furthermore, the cell type that expressed the highest levels of CD1 .1 was the splenic marginal zone B cell, a distinct subset of B cells that also expresses CD21 (the C3d receptor) and may be involved in nat ural responses to bacterial Ags, Altogether, the results support the i dea that CD1.1 may function in recruiting a form of innate help from s pecialized cytokine producer alpha beta T cells to APCs, a role that m ight be important at the preadaptive phase of immune responses to some microbial pathogens.