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100 SECTIon II Immunology ` Immunology—cellular componentS Immunology ` Immunology—cellular componentS

Major
histocompatibility MHC encoded by HLA genes. Present antigen fragments to T cells and bind T-cell receptors
complex I and II (TCRs).
MHC I MHC II
locI HLA-A, HLA-B, HLA-C HLA-DP, HLA-DQ, HLA-DR
MHC I loci have 1 letter MHC II loci have 2 letters
BIndIng TCR and CD8 TCR and CD4
Structure 1 long chain, 1 short chain 2 equal-length chains (2 α, 2 β)
eXpreSSIon All nucleated cells, APCs, platelets (except RBCs) APCs
FunctIon Present endogenous antigens (eg, viral or Present exogenous antigens (eg, bacterial
cytosolic proteins) to CD8+ cytotoxic T cells proteins) to CD4+ helper T cells
antIgen loadIng Antigen peptides loaded onto MHC I in RER Antigen loaded following release of invariant
after delivery via TAP (transporter associated chain in an acidified endosome
with antigen processing)
aSSocIated proteInS β 2 -microglobulin Invariant chain
Structure Peptide
Peptide-binding groove

α 2 α 1 α 1 β 1

α 3 α 2 β 2
β 2 −Microglobulin
Extracellular space
Cell membrane

Cytoplasm

HLA subtypes associated with diseases
hla SuBtype dISeaSe mnemonIc
A3 Hemochromatosis HA3mochromatosis
B8 Addison disease, myasthenia gravis, Graves Don't Be late(8), Dr. Addison, or else you'll send
disease my patient to the grave
B27 Psoriatic arthritis, Ankylosing spondylitis, PAIR. Also called seronegative arthropathies
IBD-associated arthritis, Reactive arthritis
C Psoriasis
DQ2/DQ8 Celiac disease I ate (8) too (2) much gluten at Dairy Queen
DR2 Multiple sclerosis, hay fever, SLE, DRive 2 multiple hay pastures
Goodpasture syndrome
DR3 DM type 1, SLE, Graves disease, Hashimoto 2-3, S-L-E
thyroiditis, Addison disease
DR4 Rheumatoid arthritis, DM type 1, Addison There are 4 walls in 1 “rheum” (room)
disease
DR5 Hashimoto thyroiditis Hashimoto is an odd Dr (DR3, DR5)

FAS1_2019_02-Immunology.indd 100 11/7/19 3:24 PM