UC San Diego

To maintain tolerance, auto-reactive B cells are deleted at different stages of development, in the bone marrow and in the periphery. The gut environment imposes unique challenges for B cells due to the need to differentiate between self-tissues, food antigens and commensal bacteria. To study B cell tolerance in the gut associated lymphoid tissues (GALT), we developed a novel mouse model in which a neo-self antigen, membrane bound duck egg lysozyme (mDEL), is specifically expressed in the

gut epithelium. The expression of mDEL in the gut was uniform and did not affect the microbiota. In this mouse model, auto-reactive B cells are deleted in the Peyer’s Patches (PP); however the population of lysozyme-specific B cells remained unaltered in the spleen. Lysozyme-specific B cells from the PP showed decreased IgM expression and increased expression of the activation marker, CD86. However, the cells did not enter the germinal center. Furthermore, mDEL expression in the gut did not induce production of lysozyme-specific IgM, IgG and IgA in the serum, suggesting that lysozyme-specific B cells did not differentiate into plasma cells upon antigen encounter. To study the survival of mature auto-reactive B cells, lysozyme-specific B cells were adoptively transferred into mice. We found the frequency of lysozyme-specific B cells to be reduced in both the PLNs and the PP if mDEL was expressed in the gut epithelium, suggesting that mature autoreactive B cells are deleted. Future experiments are aimed at analyzing the mechanisms by which B cell tolerance is maintained in the gut.