Effect of c-fos overexpression on development and proliferation of peritoneal B cells.

We examined effects of c-fos overexpression on the development and property of peritoneal B-1 cells using transgenic (H2-c-fos) mice carrying the c-fos gene under the control of the constitutive H-2Kb promoter. The number of B-1b cells in the peritoneal cavity of H2-c-fos mice was 4-fold larger than that in control littermates. Although the numbers of total peritoneal B cells and B-1a cells were similar between them, the peritoneal B-2 cell number in H2-c-fos mice was reduced to 50% of control littermates, suggesting the effect of c-fos overexpression on a balance of B-1b and B-2 cells in a peritoneal cavity. Adoptive transfer experiments with hematopoietic stem cells of H2-c-fos and control mice into irradiated H2-c-fos mice demonstrated that the augmentation of B-1b cells is due to the c-fos effect in B cells and the effect on environment of the peritoneal cavity of H2-c-fos mice. When peritoneal B cells were cultured with LPS in the presence or absence of IL-4, cell proliferation of B-1b cells was the highest among these peritoneal B cell subsets, and the proliferation of H2-c-fos B-1b cells was 3-fold higher than that of control B-1b cells. This augmentation is due to the c-fos effect in B cells. IgG1 production of B-1b cells in these cultures was slightly higher than those of B-1a and peritoneal B-2 cells. Thus, the c-fos overexpression augments development of B-1b cells in a peritoneal cavity and proliferation of peritoneal B-1b cells to LPS.