Lecture-9 Major Histocompatibility Complex and Mixed Lymphocyte Reaction

To appraise HLA polymorphism in the population and to appreciate the role of HLA in organ transplantation through MLR test. Furthermore, to familiarize the role of HLA in antigen presentation.

1. Lecture-9 HUMAN LEUKOCYTYE ANTIGEN (HLA/MHC) and MIXED LYMPHOCYTE REACTION (MLR) Prof. Sreerama Krupanidhi Email: [email protected]

2. Objectives To understand the types of HLA molecules. To acquaint with the nomenclature of HLA. To be aware of HLA genes and their location. To appraise HLA polymorphism in the population. To appreciate the role of HLA in organ transplantation through MLR test To familiarize the role of HLA in antigen presentation. 30-08-2024 2 Prof. Sreerama Krupanidhi

3. Expected Outcomes Able to distinguish between SELF and non-SELF molecules. Types, structure, genes, polymorphism and distribution of HLA class I and class II will be known as a prelude to the surgical organ transplantation. The role of MLR test in the organ transplantation will be known. 30-08-2024 Prof. Sreerama Krupanidhi 3

4. What is HLA? What is it for? Human Leukocyte Antigen Function: To present foreign peptides to T cells, thus allow to arouse immune response to eliminate foreign particles/pathogens 30-08-2024 4 Prof. Sreerama Krupanidhi

5. MHCs/HLAs are Glycoproteins 30-08-2024 5 Central Molecules in Immune information conveyance HLA gp I: Expressed on all nucleated cells. HLA I: A ; B; C; E; E ; F; G HLA gpII : Expressed on APCs HLA II: DP; DQ; DR; DM Prof. Sreerama Krupanidhi

6. Differential distribution of MHC molecules Tissue MHC class I MHC class II T cells +++ +/- B cells +++ +++ Macrophages +++ ++ Other APC +++ +++ Thymus epithelium + +++ Neutrophils +++ - Hepatocytes + - Kidney + - Brain + - Erythrocytes - -

7. Human Karyotype showing HLA gene complex location 30-08-2024 Prof. Sreerama Krupanidhi 7

8. 4 Mb 3 Mb 2 Mb 1 Mb 0 Mb HLA-A HLA-C HLA-B HLA-DR HLA-DQ HLA-DP p q Centromere Chromosome 6 30-08-2024 Prof. Sreerama Krupanidhi 8

9. HLA genes MHC locus : On chromosome 6 30-08-2024 9 Prof. Sreerama Krupanidhi

10. Structure of HLA 30-08-2024 10 Glycoproteins and Heterodimers . Structure of HLA molecules of both classes enables antigen binding and contact with T cell receptors. Extracellulary located peptide binding cleft. Polymorphic (predominantly in the cleft). Nonpolymorphic part of the molecule contains binding sites for the T cell molecules CD4 and CD8 Prof. Sreerama Krupanidhi

11. Crystal structure of peptide binding to the cleft 30-08-2024 11 Foreign peptide Prof. Sreerama Krupanidhi

12. Cleft geometry Peptide l f V. \ y P-chain MHC class I accommodates peptides of 8-10 amino acids MHC class II accommodates peptides of >13 amino acids

13. HLA Nomenclature 30-08-2024 13 Prof. Sreerama Krupanidhi

14. Limited diversity in HLA gene polymorphism due to breeding bottle-neck in recent past leaves cheetahs exceptionally susceptible to viral infections. (6 th Ed. P. 206). Heterozygosity is a survival adaptation . HLA Haplotypes of the population of Andhra Pradesh, India: 1. A*01-B*57- DRB1 *07; 2.A*33-B*44-DRB1*07; 3. A*02-B*40- DRB1 *15; 4. A*24-B*07- DRB1 *15; 5. A*24-B*40- DRB1 *15;

15. HLA Polymorphism 30-08-2024 15 Prof. Sreerama Krupanidhi

16. HLA vs. Transplantation • HLA matching between the donor and recipient - a predictor of graft survival in the kidney allograft patient • HLA mis-matches may cause chronic pathologies in the allograft • It is clear that a negative HLA-A2 recipient receiving an allograft expressing HLA-A2 will have a much higher risk of humoral rejection of the vascular endothelium. IMMUNE GRAFT REJECTION

17. Mixed lymphocyte reaction (MRL) ● D etermination of T lymphocytes alloreactivity ● M ixed donor and recipient lymphocytes → T lymphocytes a fter recognition of allogeneic MHC gp activate and proliferate One-way MRL ● D etermination of recipient T lymphocytes reactivity against donor cells ● D onor cells treated with chemotherapy or irradiated to lose the a bility of proliferation 30-08-2024 Prof. Sreerama Krupanidhi 17

18. Mixed lymphocyte reaction (MRL) ● D etermination of T lymphocytes alloreactivity ● M ixed donor and recipient lymphocytes → T lymphocytes after recognition of allogeneic MHC gp activate and proliferate One-way MRL ● D etermination of recipient T lymphocytes reactivity against donor cells ● D onor cells treated with chemotherapy or irradiated to lose the a bility of proliferation 30-08-2024 Prof. Sreerama Krupanidhi 18

19. Mixed lymphocyte reaction (MRL) 30-08-2024 Prof. Sreerama Krupanidhi 19

20. MLR 30-08-2024 20 Prof. Sreerama Krupanidhi

21. Summary Function of HLA while presenting a foreign peptide to T-cell is elucidated. Types of HLAs are familiarized. Location of HLA gene complex on Chromosome 6 between 6p21.1 to 6p22.1 cM is shown. Structure of HLA including cleft geometry is displayed. HLA haplotypes of Andhra Pradesh (India) and its nomenclature are appreciated. The role of HLA in organ transplantation is shown. 30-08-2024 21 Prof. Sreerama Krupanidhi

22. Study Questions What are HLA? Explain their structure and function. How do HLA I and II convey the information to T-cells? Describe. Enlist distribution of HLA I and II in human cells. Indicate the gene location of HLA gene complex. Elaborate on HLA polymorphism and HLA haplotypes in the state of Andhra Pradesh (India). What is MLR? How does this test help the doctor for the surgery in organ transplantation? 30-08-2024 22 Prof. Sreerama Krupanidhi

23. Acknowledgements 8/30/2024 We acknowledge the online resources and public domains for the Preparation of the content to develop teaching material and for the dissemination of knowledge. Prof. Sreerama Krupanidhi 23

24. Thank you 30-08-2024 24 Prof. Sreerama Krupanidhi