Germinal Centers and Antigen Induced BCell Differentiation

Germinal centers arise within 7-10 days after initial exposure to a thymus-dependent antigen. During the first stage of germinal-center formation, activated B cells undergo intense proliferation. These proliferating B cells, known as centro-blasts, appear in human germinal centers as a well-defined dark zone (Figure 11-17). Centroblasts are distinguished by their large size, expanded cytoplasm, diffuse chromatin, and absence or near absence of surface Ig. Centroblasts eventually give rise to centrocytes, which are small, nondividing B cells that now express membrane Ig. The centrocytes move from the dark zone into a region containing follicular dendritic cells called the light zone, where some centrocytes make contact with antigen displayed as antigen-antibody complexes on the surface of follicular dendritic cells. Three important B-cell differentiation events take place in germinal centers: affinity maturation, class switching, and formation of plasma cells and memory B cells. In general, affinity maturation and memory-cell formation require germinal centers. However some class switching and significant plasma-cell formation occur outside germinal centers.

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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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