Monoclonal immunoglobulin A derived from peritoneal B cells is encoded by both germ line and somatically mutated VH genes and is reactive with commensal bacteria.

We transferred peritoneal cells from BALB/c mice into C.B17 scid/scid mice. Six to eight months after injection, only cells with the B1 phenotype were retained in the spleens and peritoneal cavities of these mice.

CH isotype switching in B cell differentiation.

We have functionally defined a number of B cell subsets that likely represent B cells at different stages of development, based on the pattern of CH isotypes expressed by their clones in splenic fragment or microcultures and on those factors necessary in culture to support the growth of a clone displaying a particular isotype or set of isotypes. Our observations are consistent with isotype switching being a stochastic process which results in the occurrence of progressive isotype restriction in members of a diversifying clone. The surface marker best predictive of the pattern of isotypes a clone may secrete is the sIg isotype of its B cell precursor.