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( Major histocompatibility complex.) The immune system is regulated by molecules coded by some genes.These are genes of the histocompatibility system which code For Human leukocyte antigens (HLA).
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MHC & INFECTIOUSDISEASES
By MAZIN S.SALMAN
.MHC (Major histocompatibility
complex).The immune system is
regulated bymolecules coded by some
genes.These are genes of the
histocompatibility systemwhich code
For Human leukocyte antigens.
(HLA.)
HLA : located in the short armof chromosome 6.( part of
MHC.)MHC: divided into 3 classes.
MHC class 1 : code the moleculesHLA-A, HLA-B, HLA-C.
(present in almost all somatic cells)MHC class11 : code the molecules
HLA-DR, HLA-DQ, HLA-DP.(expressed in APC , B- cells, activated
T-cells, macrophages, dendritic cells,Thymic epith.cells).
Each individual have: *2 antigens in each locus.
*one half inherited from each parent.
Expression of MHC alleles isCodominant.
(one haplotype inherited from each parent ).
HLA: the most polymorphicgenetic system in man.
*numerous alleles. *various possible combinations.
*Polymorphism contribute to: -the genetic diversity of the
species. -differences in susceptibility to
diseases.(among genetically distinct groups).
*this make it difficult for large-scale epidemics to occur.
MHC polymorphism &polygeny.
Polymorphism of MHC loci ensure thediversity in MHC gene expressionin the population as a whole.Polygeny (the presence of several differentrelated genes with similar functions) , ensuresthat each individual produces a numberof different MHC molecules.
The antigenic universe.Scientists estimate that the antigenic universecontain between - epitopes.(antigens.)This mean that there are at least - epitope –specific T-celland B-cell.(specific mean that there is a cell, T orB for each of the - epitopes.)
T-cells only recognize microbialpeptides in association withMHC.(restricted)
*MHC control :-resistance to infections.
-susceptibility to infections.Stimulation require 2 signals.
*Antigen peptide. *Co-stimulatory signal.
(2 key system).
*HLA-DRB1*7 and HLA-DQA1*0101:are associated with greater
susceptibilityto develop pulmonary T.B.
*HLA-DQA1*0301 &HLA-DQA1*0501:are associated with protection
against T.B.
Conclusion *HLA may act alone (or with other
genes )in conferring susceptibility to , or
protectionagainst , infectious diseases.
*Knowledge about genetic mechanisms
contribute to our understanding of the
pathogenesis of infectious diseases. *The mechanism of immune
responses toinfections that are influenced by HLA
may be the key to future vaccines.
* Future vaccines aim to use peptidesof the organisms that mimic the HLAantigens