A Level Biology Practice Exam

The major histocompatibility complex (MHC) plays a crucial role in the immune system, particularly in the activation of T cells, which are essential for the adaptive immune response. The significance of MHC lies in its ability to present processed antigenic pieces (peptides) to T cells. This process is vital for the recognition of foreign antigens, such as those derived from pathogens.

When a pathogen invades the body, its proteins are broken down into smaller peptides. These peptides are then loaded onto MHC molecules and transported to the surface of antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells. T cells, equipped with T cell receptors (TCRs), recognize these peptide-MHC complexes. This interaction activates T cells, leading to an immune response that can target and eliminate the pathogen.

The other options describe functions that do not accurately represent the primary role of MHC in the immune response. For instance, while MHC does help in distinguishing self from non-self through the recognition of self-antigens, its main focus is on antigen presentation to T cells. The binding of antibodies to pathogens is a different aspect of the immune system involving B cells and does not directly relate to MHC functions