Figure 1: An abridged view of B-cell development before foreign antigen stimulation. Note that B1 cells have not been identified in humans though analogous cells have been observed on serosal surfaces. This process of pre-foreign antigen-driven development of B cells yields three populations of B cells, namely, B1 cells, marginal zone B cells, and follicular B cells. The next panel (pink background) illustrates a condensed developmental ontogeny following activation by foreign antigen. The marginal zone cells are capable of developing into mutated, class-switched B-cell receptors