What is the difference between a professional and non-professional APC?

• professional APC's exress high levels of MHC's and co-stimulatory molecules
• non-professional APC's express MHC, but in lower levels

• single alpha chain
• complexed with beta-2 globulin

• binds to molecules other than short cell-derived peptides
• examples
  • CD1 bind glycolipids and present to NKT cells and some gamma-delta TCR
  • FcdRN bind IgG molecules and transport the IgG across placenta and protect adult IgG from degredation
  • HLA-E bind signal sequences from MHC I proteins and present peptides to NK cells

• bind peptides usually at end of peptide
• relatively conserved anchor sequence that is shorter in length (8-10 AA)

• bind to peptides by interaction along binding groove
• tend to bind peptides that are loner and more variable in length (13-18 AA)

• MHC I recognize CD8/Tc receptors
• MHC II recognize CD4/Th receptors

• MHC I recognize endogenous antigens to cause CD8 T cell response
• MHC II recognize exogenous antigens to cause CD4 T cell response

1. MHC I complexed with calnexin
2. Calnexin is removed and is replaced by Tapsain, calrecticulin, and beta globulin protein
3. protesome degrade peptide
4. peptide binds, leading to exit of calrecticulin and tapsain
5. MHC I exit rER via TAP transporter

• if you have no TAP, it leads to bare lymphocyte syndrome
• complication- patient more susceptible to viruses

1. invariant chain binds in the groove of the MHC II
2. leaves the ER
3. CLIP will enter after digested invariant chain leaves
4. CLIP is released so endosomal material can enter binding site

• heterodimer of alpha and beta components

Explain the phenomenon of cross presentation of antigens. What is the advantage of this phenomenon?

• after entering MHC II pathway, peptide is divereted from endosomal compartment into the proteosome, leading to it going down the MHC I pathway
• it presents antigens from avoiding the immune system (some viruses have evolved ways to block entrance into endosomal compartments of the cell)

• MHC I
  • A, B (most diverse), C
• MHC II (each of these can have an alpha or beta)
  • DP
  • DQ
  • DR (one with beta most diverse)

MHC gene locus is located in what chromosome

• genetic polymorphism
  • multiple alleles of MHC are expressed codominantly (each allele from parent expressed), which allow for diversity within species

• peptide binding
• TCR contact regions of MHC molecules

• TCR cross reacts with non-self MHC strongly and peptide weakly
• TCR react with peptide strongly or MHC weakly

SEEN IN REJECTION OF ORGANS!!!!

• MHC I- all nucleated cells of body
• MHC II- APC's