27 BIO 326R T Cells

27 BIO 326R T Cells - BIO 326T T cells Major...

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Unformatted text preview: BIO 326T T cells Major Histocompatibility Complex A set of genes associated with recognition and antigen presentation to T cells Also called the HLA complex in humans e.g. HLA B-27 “ Antigen” in this case just means a small peptide. This peptide may be self or non-self. The immune system’s ability to discriminate between the two is vital. Class I MHC genes are expressed on the surface of all nucleated cells , they present antigens to cytotoxic T cells There are “classical” and non-classical Class I genes – we will be talking almost exclusively about classical class I genes as above Class II genes are expressed on “professional antigen presenting cells:” B cells, macrophages and dendritic cells . They present antigens to T helper cells As with Class I, there are classical and non-classical class II genes, such as TAP and HLA-DM, we will discuss classical class II almost exclusively Class III genes encode various secreted proteins (including some complement and inflammatory molecules), heat shock proteins, peptide transporters… Major Histocompatibility Complex genetics The genes of the MHC are located in a cluster and are very tightly linked: all the MHC genes are usually inherited as a set from each parent Little crossing over is seen within the MHC The actual physical size of the MHC locus is larger than you would calculate from a genetic mapping study (genetic mapping is based on measuring number of crossovers, which, again, are rare within the MHC) The MHC complex is also highly polymorphic: there are a large number of small variations (akin to point mutations) between individuals i.e. there are lots and lots of different MHC alleles within the human population In an outbred population (such as humans), most individuals will be heterozygous at the MHC The chances of two siblings being histocompatible (having the same haplotype) is roughly one in four (assuming mother and father have different haplotypes). None of the siblings should be histocompatible with the parents Transplants are rejected due to CTLs recognizing the transplanted MHC class I appearing foreign – independent of the peptide displayed in class I Alleles are codominant with regard to histocompatibilty and Mendelian genetics i.e. the effects of both alleles are seen when doing a transplant. If either of the alleles is incompatible, the transplant will be rejected Differences between MHC genes is often found to be the reason why different individuals will vary in their susceptibility to a disease Punnett square for those who forgot genetics HLA B-27/HLA B-14 HLA B-32 /HLA B-17 B-32 (Paternal) B-17 (Paternal) B-27 (Maternal) B-27/B-32 B-27/B-17 B-14 (Maternal) B-14/B-32 B-14/B-17 Remember that the HLA alleles are usually inherited as a set!...
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27 BIO 326R T Cells - BIO 326T T cells Major...

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