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Chapter

MICR 3230 Chapter Notes -Antigen, Glycoprotein, Lysosome


Department
Microbiology
Course Code
MICR 3230
Professor
Azad Kaushik

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The Major Histocompatibility Complex and Antigen Presentation (Chapter 8) Summary
- MHC encodes class I, II molecules functioning in antigen presentation to T cells,
class III molecules with diverse functions
- MHC genes tightly linked and generally inherited as a “block” from parents
groups of alleles called haplotypes
- MHC genes are polymorphic – many alleles exist for each genes – polygenic –
many different genes exist
-Class II molecules large glycoprotein chain and β2-microglobulin, protein
with a single domain
- Class I molecules expressed on almost all nucleated cells
- Class II molecules restricted to B cells, macrophages & dendritic cells * APC
- Proteasomes and transporters involved in antigen processing (before T cell
recognition)
- MHC alleles influence immune responsiveness and antigen presenting ability
also susceptibility to many diseases
- Class I molecules present endogenous antigen to CD8+ TC cells
- Class II molecules present exogenous antigen to CD4+ TH cells
- Endogenous antigens degraded into peptides within cytosol by proteasomes
- Class I molecule assembly in the rough endoplasmic reticulum presented on
membrane to CD8+
- Exogenous antigens are internalized and degraded within acidic endocytic
compartments (early, late, lysosome) and combine with class II molecules for
presentation to CD4+
- Peptide binding to class II involves replacing a fragment of invariant chain in the
peptide binding cleft by a process catalyzed by non-classical MHC molecule
HLA-DM
- Exogenous peptide antigen in certain cell types may gain access to class I
presentation pathways via phagosomes in a process called cross-presentation
- Presentation of non-peptide antigen (lipid/glycolipid) derived from bacteria (ie.
tuberculosis) involves the class I-like CD1 molecule family
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