Veterinary Immunology and Serology

ANTIGEN PROCESSING AND PRESENTATION

Processing of Exogenous antigen

• The processing and presentation of exogenous protein antigen is mainly done by the antigen presentating cells viz. macrophages, dendritic cells and B-cells, controlled by MHC-Class II molecule. These cells can phagocytose exogenous antigen and process this antigen in the phagosome and finally phagosome containing processed peptides fused with the endosome containing MHC-Class -II molecules.
• In the phago-endosome the processed peptides are loaded on to the MHC-class II  molecules and then presented on to their surface. CD4⁺T helper cells recognize these peptides along with MHC- Class II  on the  surface of antigen presentating cells for the initiation of immune response.

Processing of Endogenous antigen

• Cytotoxic T cells recognize antigen in the context of MHC class I antigen on the surface of viral infected cells or transformed cells in the body. The endogenous antigens (viral antigens or transformed proptein molecules ) are processed by the immunoproteosomes in the cytosol of a cell and appropriate peptide is selected by the two transporter proteins -TAP1 & TAP2 and transported to the endoplasmic reticulum for loading to the MHC class I molecule. Then the peptide along with MHC class I molecules is transported to the srface of cell which is now recognozed by the cytotoxic T cells for its lysis.

Presentation of Non peptide antigen

• It is well known that non proten antigen like glyolipids and lipids  are recognize by T cells . These non protein antigen are presented by the members of CD1 family of non classical class I molecules .