Cell Maturation

The generation of mature B cells first occurs in the embryo and continues throughout life. Before birth, the yolk sac, fetal liver, and fetal bone marrow are the major sites of B-cell maturation; after birth, generation of mature B cells occurs in the bone marrow.

VISUALIZING CONCEPTS

VISUALIZING CONCEPTS

ANTIGEN-INDEPENDENT PHASE (maturation)

CD45R (B220) surface marker

ANTIGEN-DEPENDENT PHASE (activation and differentiation)

ANTIGEN-INDEPENDENT PHASE (maturation)

CD45R (B220) surface marker

Antigen Dependent Phase
5 x 106 per day

ANTIGEN-DEPENDENT PHASE (activation and differentiation)

Peripheral lymphoid organ

Cd45r B220

Peripheral lymphoid organ

FIGURE 11-1

Overview of B-cell development. During the antigen-independent maturation phase, immunocompetent B cells expressing membrane IgM and IgD are generated in the bone marrow. Only about 10% of the potential B cells reach maturity and exit the bone marrow. Naive B cells in the periphery die within a few days unless they encounter soluble protein antigen and ac tivated Th cells. Once activated, B cells proliferate within secondary lymphoid organs. Those bearing high-affinity mIg differentiate into plasma cells and memory B cells, which may express different isotypes because of class switching. The numbers cited refer to B-cell development in the mouse, but the overall principles apply to humans as well.

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