C4B

C4B

C4B is a protein that is part of the complement system, which plays a crucial role in the immune response. The complement system is a group of proteins that work together to fight infections and clear damaged cells. C4B is one of the components of the C4 protein, which is involved in the classical and lectin pathways of complement activation.

Structure

C4B is encoded by the C4B gene, which is located on chromosome 6 in humans. The C4 protein is a large glycoprotein that is cleaved into three fragments: C4a, C4b, and C4c. The C4B variant differs from its closely related counterpart, C4A, by four amino acids, which affect its binding properties and function.

Function

C4B plays a critical role in the activation of the complement system. When the complement system is activated, C4 is cleaved by the enzyme C1s into C4a and C4b. The C4b fragment then binds covalently to the surface of pathogens or cells, where it acts as an opsonin, marking them for destruction by phagocytes. C4b also forms part of the C3 and C5 convertase complexes, which are essential for the amplification of the complement cascade.

Clinical Significance

Deficiencies or polymorphisms in the C4B gene can lead to various immune-related disorders. A deficiency in C4B can result in increased susceptibility to infections and autoimmune diseases such as systemic lupus erythematosus (SLE). The presence of certain C4B alleles has been associated with a higher risk of developing autoimmune conditions.

Genetic Variability

The C4B gene exhibits a high degree of genetic variability, with multiple alleles present in the human population. This variability can influence the level of C4B protein expression and its functional activity. The gene is part of the major histocompatibility complex (MHC) region, which is known for its genetic diversity and role in immune function.

Research and Future Directions

Ongoing research is focused on understanding the precise role of C4B in immune regulation and its involvement in disease processes. Advances in genomics and proteomics are providing new insights into the function of C4B and its interactions with other components of the immune system. Understanding these interactions may lead to novel therapeutic approaches for treating immune-related diseases.

See Also

• Complement system
• C4A
• Immune system