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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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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