What is the MHC class restriction for CD4 T cells?

CD4 T cells are specifically restricted to recognizing antigens presented by MHC class II molecules. This restriction is crucial for their function in the immune response. MHC class II molecules are mainly expressed by professional antigen-presenting cells such as macrophages, dendritic cells, and B cells. When these cells process and present antigens via MHC class II, CD4 T cells can then bind to these complexes, leading to their activation.

The binding of CD4 T cells to MHC class II molecules facilitates a range of immune responses, including the activation of B cells to produce antibodies and the enhancement of cytotoxic T cell responses. This interaction exemplifies how the adaptive immune system can specifically target pathogens based on the type of MHC molecule presenting the antigen.

Understanding this restriction is key in immunology, particularly in the context of vaccination, autoimmunity, and transplant rejection, where MHC compatibility between donors and recipients is critical. The other options—MHC class I, MHC class III, and MHC class IV—do not relate to CD4 T cell activation directly; MHC class I is primarily recognized by CD8 T cells, while MHC class III is involved in various immune functions but does not present peptides to T cells