Question

The antigen receptor on a T cell recognizes a degraded fragment of a protein (i.e., a peptide) bound to a specialized cell surface peptide-binding receptor called an MHC molecule. One key aspect of this system is that the peptides displayed on MHC molecules can be derived from intracellular proteins. This mode of antigen recognition is particularly important in allowing the adaptive immune response to detect infections by? please explain

a. Fungi that form hyphae in the bronchial airways

b. Fungal infections in the skin epithelium

c. Intracellular pathogens, such as viruses and some protozoa

d. Large helminthic parasites in the gastrointestinal tract

e. Extracellular bacteria that colonize the lungs

Answer 1

Antigenic peptides that displayed on the MHC molecules may be endogenously synthesized or may be exogenous.

In case b( fungal infections in the skin epithelium) and e( Extracellular bacteria that colonize the lungs), the peptides produced by these bacteria and fungi are exogenous. These peptides bind with the MHC II molecule and presented on the cell surface. When there is T helper cell(TH2) crossing by, then it recognises the foreign antigen and attached with it through CD4 receptor and destroy it.

While in other case like , intracellular pathogens ( such as viruses and protozoa) produces intracellular peptides. These peptides are recognized by MHC I as endogenous and presented on cell surface. It got recognized by T cytotoxic cell and attached to it with CD 8 receptor.