Abstract
Antibodies against bacterial capsular polysaccharides play a critical protective role. Responses to these antigens can occur without the help or control of T cells and are associated with marginal zone (MZ) B cells. Capsular antigens are diverse and some cross‐react with self‐carbohydrate epitopes. This diversity may explain the recruitment of non‐autoreactive recirculating B cells and memory B cells to the MZ in addition to other B cells, some of which are weakly autoreactive cells, that are recruited to the MZ without entering the recirculating pool. To test whether memory B cells respond to polysaccharide‐based antigens, mice with hapten‐specific memory B cells were challenged with hapten‐polysaccharide. Hapten‐specific plasma cells producing high affinity antibody with IgV‐region mutations were induced. To test whether naive recirculating B cells can form MZ cells that respond to polysaccharide, recirculating B cells from lymph nodes were transferred into Rag‐1‐deficient mice. MZ cells differentiated from the donor cells without proliferation or T cell help and responded to polysaccharide‐based antigen. The differentiation of B cells both from germinal centers and the recirculating pool to the MZ phenotype is likely to make an important contribution to the repertoire of B cells that respond to polysaccharide antigens.