( 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).

1. MHC &
INFECTIOUS
DISEASES

2. By
MAZIN S.SALMAN

4. .MHC
( 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).

5. HLA : located in the short arm
of chromosome 6.( part of MHC.)
MHC: divided into 3 classes.
MHC class 1 : code the molecules
HLA-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.)

9. Each individual have:
* 2 antigens in each locus.
* one half inherited from each parent.
Expression of MHC alleles is
Codominant.
each ( one haplotype inherited from
parent .)

10. HLA: the most polymorphic
genetic 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.

11. MHC polymorphism &polygeny.
Polymorphism of MHC loci ensure the
diversity in MHC gene expression
in the population as a whole.
Polygeny (the presence of several different
related genes with similar functions) , ensures
that each individual produces a number
of different MHC molecules .

13. The antigenic universe.
Scientists estimate that the antigenic universe
contain between 106- 107
epitopes.(antigens.)
This mean that there are at least
106- 107 epitope –specific T-cell
and B-cell.
(specific mean that there is a cell, T or
B for each of the 106- 107 epitopes.)

16. T-cells only recognize microbial
peptides in association with
MHC.(restricted)
* MHC control :
-resistance to infections.
-susceptibility to infections.
Stimulation require 2 signals.
*Antigen peptide.
* Co-stimulatory signal.
(2 key system .)

28. *HLA-DRB1*7 and HLA-DQA1*0101:
are associated with greater susceptibility
to develop pulmonary T.B.
*HLA-DQA1*0301 &HLA-DQA1*0501:
are associated with protection against T.B
.

30. Conclusion
* HLA may act alone (or with other genes )
in conferring susceptibility to , or protection
against , infectious diseases.
* Knowledge about genetic mechanisms
contribute to our understanding of the
pathogenesis of infectious diseases.
* The mechanism of immune responses to
infections that are influenced by HLA
may be the key to future vaccines.

31. * Future vaccines aim to use peptides
of the organisms that mimic the HLA
antigens