What is the primary function of MHC class I molecules?

• A. Presenting antigens to CD4-positive T cells
• B. Presenting antigens to CD8-positive T cells
• C. Regulating B cell activity
• D. Facilitating communication between T cells

Answer: (B)

The primary function of MHC class I molecules is to present antigens to CD8-positive T cells, also known as cytotoxic T lymphocytes. These molecules are found on the surface of nearly all nucleated cells in the body and play a crucial role in the immune response. When a cell is infected by a virus or undergoes malignant transformation, it presents fragments of intracellular proteins (antigens) on its MHC class I molecules.

CD8-positive T cells, which are vital for eliminating infected or cancerous cells, have specific receptors (T cell receptors) that recognize the antigen-MHC class I complex. Once a CD8-positive T cell binds to its corresponding antigen presented by MHC class I, it becomes activated and can kill the infected or abnormal cell.

This mechanism is essential for cellular immunity, ensuring that the immune system can identify and destroy cells that are compromised or pose a threat to the organism. The other options involve functions associated with different aspects of the immune system, such as communication between T cells or interaction with CD4-positive T cells, which primarily recognize antigens presented by MHC class II molecules. Thus, the focus of MHC class I molecules clearly aligns with the presentation of antigens specifically to CD8-positive T cells