Final answer:
MHC II molecules are composed of α (alpha) and β (beta) chains that bind peptides and present them to CD4+ T cells, typically found on antigen-presenting cells. They are crucial for the immune system's ability to recognize and respond to pathogens.
Step-by-step explanation:
MHC II molecules are made up of two chains called α (alpha) and β (beta) whose function is to bind peptides and present them to CD4+ T cells. MHC II molecules have two protein chains of roughly equal size, forming a complex that displays processed foreign antigens to immune cells. These molecules are critical for the immune system to recognize and respond to pathogens.
MHC II molecules are expressed only on the surface of antigen-presenting cells (APCs), such as macrophages, dendritic cells, and B cells. Their main role in the adaptive immune system is to present abnormal or non-self-pathogen antigens for the preliminary activation of T cells. This, in turn, is crucial for mounting an appropriate immune response.
The antigen presentation with MHC II is vital for the immune system's ability to distinguish between healthy/normal cells and those infected or cancerous. The binding of MHC II molecules to CD4+ T cells is a key step in the adaptive immune response, leading to the activation of these T cells and subsequent immune actions.