8 For each of the following cell components or processes ind

8.   For each of the following cell components or processes, indicate whether it is involved in the processing and presentation of exogenous antigens (EX), endogenous antigens (EN), or both (B). Briefly explain the function of each item.
a.   _____Class I MHC molecules
b.   _____Class II MHC molecules
c.   _____Invariant chain.
d.   ____Tap 1 and Tap 2 proteins
e.   ____Transport of vesicles from RER to the Golgi complex
f.   ____Proteasomes
g.   ____Phagocytosis or endosytosis
h.   ____Calnexin
i.   ____CLIP
j.   ____Tapasin

Solution

Answer :

Endogenous antigens are forgein antigens which are synthesised inside the body cells which includes the viral proteins produced after a virus infects the cell or the abnormal prteins synthesisd by cancerous cells.Fragments of endogenous antigens are processed and presented by antigen presenting cells through class I MHC molecules. T cells displaying CD8 recognize antigen associated with class I MHC molecules and thus are said to be class I MHC restricted.

Exogenous antigens: Exogenous antigen is produced outside of the host cell and enters the cell by endocytosis or phagocytosis. These antigens includes bacteria and bacterial toxins, parasitic worms, inhaled pollen or dust, Antigenpresenting cells (macrophages, dendritic cells, and B cells) degrade ingested exogenous antigen into peptide fragments within the endocytic processing pathway. APCs then present the fragments to T helper cells (CD4⁺) by the use of class II histocompatibility molecules on their surface.