Centroblast

Histopathology of a centroblast in follicular lymphoma

Model of Centroblast Development

Centrocyte, centroblast and follicular dendritic cell in a follicular lymphoma

Centroblast is a type of B cell found within the germinal centers of lymph nodes. These cells are large, dividing lymphocytes that are characterized by their round shape, vesicular nuclei, and lack of surface immunoglobulin. Centroblasts are crucial in the immune system's response to antigens, playing a key role in the process of affinity maturation and the generation of memory B cells and plasma cells.

Characteristics

Centroblasts are distinguished from other B cells by several key features:

• Large size: They are larger than resting B cells.
• Nucleus: Their nuclei are round, often with multiple nucleoli, and the chromatin is less condensed, giving it a lighter appearance under the microscope.
• Lack of surface immunoglobulin: Unlike most B cells, centroblasts do not express immunoglobulin on their surface, as they are in a stage of rapid division and differentiation.
• High proliferation rate: They are among the most rapidly dividing cells in the body during an immune response.

Function

The primary function of centroblasts is to undergo somatic hypermutation, a process that introduces mutations into the variable region of the immunoglobulin genes. This process is critical for affinity maturation, whereby B cells producing antibodies with higher affinity for the antigen are selected for further development. After several rounds of division and mutation, centroblasts differentiate into either centrocytes, which are smaller B cells that express surface immunoglobulin and are subject to selection based on the affinity of their B cell receptor, or directly into memory B cells or plasma cells.

Pathology

Abnormal proliferation or dysfunction of centroblasts can lead to lymphoma, particularly diffuse large B-cell lymphoma (DLBCL), which is characterized by the rapid growth of tumors consisting of large B cells, including centroblasts. The identification and classification of centroblasts are important in the diagnosis and treatment of such lymphomas.

In the Germinal Center Reaction

Within the germinal center, centroblasts are found in the dark zone, where they proliferate and undergo somatic hypermutation. The germinal center reaction is a tightly regulated process that ensures the production of high-affinity antibodies necessary for effective immune protection. Centroblasts transition to centrocytes and move to the light zone of the germinal center, where they are selected for high-affinity interactions with antigen presented on follicular dendritic cells.

Conclusion

Centroblasts play a critical role in the adaptive immune response, particularly in the production of high-affinity antibodies. Their study is essential for understanding immune responses to pathogens, vaccine development, and the pathology of B-cell lymphomas.