7: T-Cell Receptors and MHCs

what are the structural similarities between antibodies and T-cell receptors?

• both are disulfide-linked heterodimers

• chains are glycoproteins

• contain constant and variable regions

what are the functional differences between antibodies and T-cell receptors?

• expression as receptor (T-cells vs. B-cells)

• antibodies bind to surface structures strongly (proteins, cabs, and lipids)

• TCR recognize short peptide fragments gathered from antigenic proteins presented by MHC molecules

what is the human major histocompatibility complex (MHC) referred to as?

human leukocyte antigen (HLA)

what is polymorphism of the classical MHC loci due to?

allelic variation

where does MHC Class I antigen loading occur?

endoplasmic reticulum

where does MHC Class II antigen loading occur?

vesicular fusion in the cytoplasm

what type of cells express MHC class I molecules?

all nucleated cells (T-cells, B-cells, macrophages, dendritic cells, neutrophils)

what type of cells express MHC class II molecules?

antigen presenting cells (B-cells, macrophages, dendritic cells)

how are MHC Class I molecules distinct from MHC Class II molecules structurally?

class I has 1 heavy chain and a smaller protein, class II has 2 similar-sized chains

from where do MHC Class I molecules bind to peptides?

intracellular antigens (viruses)

from where do MHC Class II molecules bind to peptides?

extracellular antigens (bacteria)

how does MHC polymorphism affect the binding of peptide antigens?

increases the likelihood that a T cell will recognize a foreign antigen since there is a wider range of peptides presented

how does a lack of polymorphism impact the quality of the immune response?

less effective immune response since certain pathogen peptides cannot be presented to T cells