What are the 3 functions of the innate immune system?

Physical/chemical barriers, cellular responses, activation of adaptive immunity

Why is MHC necessary?

T cells can’t recognize free antigen → need MHC to present peptide→ enables T cell activation

Similarities between BCR and TCR?

Both are antigen-specific and generated by gene rearrangement

Differences between BCR and TCR?

BCR binds free antigen (no MHC); TCR requires processed antigen + MHC

What is self-MHC restriction?

T cells only recognize antigen on self-MHC

Where are MHC molecules expressed?

Most cells (Class I), APCs (Class II)

Where are TCRs expressed?

Only on T cells

Components of MHC Class I?

α chain + β2-microglobulin

Components of MHC Class II?

α chain + β chain

Similarity between Class I & II?

Both have peptide-binding groove and present antigens to T cells

Key difference between Class 1 and 2?

Class 1 = 1 chain + β2m; Class 2 = 2 chains

Where is MHC Class I found?

All nucleated cells

Where is MHC Class II found?

APCs (Dendritic cells, macrophages, B cells)

What is the binding groove?

Site where peptide binds on MHC

Why is the binding groove important?

Determines which peptides can be presented

Steps of antigen presentation?

Breakdown → load on MHC → move to surface → T cell recognition

What is the central dogma?

DNA → RNA → Protein

What is an Allele?

Different versions of a gene

What is an Allotype?

Protein product of allele

What is a SNP?

a polymorphism of a single nucleotide (not quite same as mutation)

What is Co-dominance?

Both alleles expressed equally

What is a Haplotype?

Linked genes inherited together

What is a Syngeneic Haplotype?

Genetically identical

What is Congenic Haplotype?

Identical except one locus

What is Polygeny?

Multiple genes → one protein

What is a Polymorphism?

Many versions of a protein due to multiple alleles

Where are MHC genes located?

Chromosome 6

What is HLA?

Human MHC known as Human Leukocyte Antigen complex

What does Complex I encode?

HLA-A, B, C

What does Complex II encode?

HLA-DP, DQ, DR

What does Complex III encode?

Complement + inflammatory cytokines

Complex I presents to which cells?

CD8 T cells

Complex II presents to which cells?

CD4 T cells

Why is co-dominance important?

Increases antigen presentation diversity

How are MHC genes inherited?

As haplotypes from each parent and expressed co-dominantly

What is MHC diversity?

Many alleles in population

Why is MHC diversity important?

Protects against many pathogens

What is MHC promiscuity?

One MHC binds many peptides

Heterozygote advantage?

More alleles = better protection

Balancing selection?

natural selection that maintains multiple alleles in a population keeping MHC diversity high

Directional selection?

Favors one allele, reducing diversity

What are anchor residues?

Key amino acids that bind MHC

Why are anchor residues important?

to determine which peptides fit in the groove

Anchor residues are more important in which class?

Class I because of more restrictive binding

MHC are related to promiscuity?

They relate to promiscuity because Class 2 have less strict binding making them more promiscuous.

How does MHC activate T cells?

Signal 1 = MHC + peptide → TCR

What else is needed for T cells activation?

Signal 2 (costimulation) + Signal 3 (cytokines)

What are the 3 signals for T cell activation?

MHC + peptide (Signal 1), Costimulation (Signal 2) and Cytokines (Signal 3)