MHC (Major Histocompatibility Complex) Flashcards
MHC (Major Histocompatibility Complex):
A group of genes encoding cell surface proteins responsible for presenting antigens to T cells, playing a key role in immune recognition.
MHC Class I:
Molecules present on the surface of all nucleated cells that present endogenous antigens to CD8+ T cells (cytotoxic T cells).
MHC Class II:
Molecules found on antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells, presenting exogenous antigens to CD4+ T cells (helper T cells).
Antigen presentation:
The process by which MHC molecules display fragments of antigens on the cell surface for recognition by T cells.
Endogenous antigens:
Antigens that originate from within the cell, such as viral proteins or mutated proteins in cancer cells, presented by MHC Class I.
Exogenous antigens:
Antigens that come from outside the cell, such as bacterial proteins, presented by MHC Class II.
CD8+ T cells:
Cytotoxic T cells that recognize antigens presented by MHC Class I molecules and kill infected or abnormal cells.
CD4+ T cells:
Helper T cells that recognize antigens presented by MHC Class II molecules and activate other immune cells, including B cells and cytotoxic T cells.
Peptide binding groove:
The region of the MHC molecule where the antigenic peptide is held for presentation to T cells.
T-cell receptor (TCR):
A receptor on T cells that recognizes and binds to the peptide-MHC complex, initiating an immune response.
Polymorphism in MHC:
MHC genes are highly polymorphic, meaning there are many variants in the population, which helps the immune system recognize a wide variety of pathogens.
MHC I structure:
Composed of a heavy α-chain and β2-microglobulin, with a peptide-binding groove that holds endogenous antigen peptides for presentation.
MHC II structure:
Composed of two chains (α and β) that form a peptide-binding groove for exogenous antigen peptides, presenting them to CD4+ T cells.
Cross-presentation:
A process where dendritic cells present exogenous antigens via MHC Class I, enabling activation of CD8+ T cells, important for viral and tumor immunity.
Antigen processing:
The process by which antigens are degraded into peptides and loaded onto MHC molecules for presentation to T cells.
Proteasome in MHC Class I pathway:
A cellular complex that degrades proteins into peptides, which are then transported into the ER and loaded onto MHC Class I molecules.
Endosomal/lysosomal pathway for MHC Class II:
The pathway where exogenous antigens are processed in endosomes/lysosomes and then loaded onto MHC Class II molecules.
MHC restriction:
The requirement that T cells only recognize antigenic peptides when they are presented by the appropriate MHC molecule.
MHC and transplantation:
MHC molecules are key in organ transplantation because mismatched MHC molecules between donor and recipient can lead to graft rejection.
MHC polymorphism and immune response:
The diversity of MHC molecules within a population allows for a broader immune response, improving the ability to combat various pathogens.
Self vs. non-self recognition by MHC:
MHC molecules help the immune system distinguish between self (normal body cells) and non-self (pathogens or infected cells).
MHC and autoimmune diseases:
Faulty MHC recognition or presentation can lead to autoimmune diseases, where the immune system mistakenly attacks the body’s own tissues.
MHC Class I deficiency:
A rare condition where mutations in MHC Class I molecules lead to impaired CD8+ T cell responses and increased susceptibility to infections.
MHC Class II deficiency:
A genetic disorder where defects in MHC Class II molecules impair CD4+ T cell function, leading to severe immune deficiency.
MHC in cancer:
Tumors can evade immune detection by altering the expression of MHC molecules or downregulating antigen presentation.
MHC in viral immune evasion:
Some viruses can inhibit MHC Class I antigen presentation, preventing the immune system from detecting and responding to infected cells.
MHC-based vaccines:
Vaccines that aim to enhance the presentation of specific antigens via MHC molecules to improve immune responses against diseases like cancer.
MHC and disease susceptibility:
Certain MHC variants are associated with increased or decreased susceptibility to various diseases, including infections, autoimmune diseases, and cancer.
