MAJOR HISTOCOMPATIBILITY COMPLEX ...pptx

Major histocompatibility complex
Microbiology notes

1. MAJOR HISTOCOMPATIBILITY COMPLEX By, Revathi R MSc Renal Sciences and Dialysis Technology (Semester II)

2. CONTENTS Introduction Definition Types of MHC molecule Structure of MHC molecule Human leukocyte antigen Function of MHC molecule

3. INTRODUCTION Major histocompatibility complex is set of surface proteins located on the cell membrane of nucleated cells . MHC molecules always recognize T Lymphocytes. It plays more important work to identify the antigen between self and non self body, intracellular recognition and responsible for antigen presentation.

4. DEFINITION : “Major histocompatibility complex is membrane attached protein which work on recognition of antigen between self and non self body and antigen presentation”

5. HUMAN LEUCOCYTE ANTIGEN (HLA) Histocompatibility antigens  cell surface antigens that evoke immune response into an incompatible host resulting in allograft rejection. Histocompatibility antigens  Alloantigens  present on the surface of leucocytes in man  Human leucocyte antigen ↓ genes coding for them  HLA complex ↓ Location – Short arm of chromosome 6

6. TYPES OF MHC MOLECULE : The MHC molecules/ HLA complex are classified into four classes namely – Class I MHC Class II MHC Class III MHC Class IV MHC

7. CLASS I MHC HLA – A, HLA – B, HLA – C Present on the surface of all nucleated cells. Involved in graft rejection and cell mediated cytolysis. CD8 – cytotoxic T cell  recognize MHC class I antigens for their action.

8. STRUCTURE AND FUNCTION – CLASS I

9. STRUCTURE AND FUNCTION – CLASS I α chain : Transmembrane glycoprotein encoded by polymorphic gene within A,B and C region of human HLA complex. Anchored in the plasma membrane by its hydrophobic transmembrane segment and hydrophilic cystoplasmic tail. β2 chain : β2 macroglobulin is a protein encoded by a highly conserved gene located on different chromosome. Similar in size and organization to α₃ domain.

10. STRUCTURE AND FUNCTION – CLASS I Bind to peptide antigens and present to CD 8 + T helper cells. CD8 T cells are specific for MHC I antigen MHC – I binds endogenous antigen and present to T helper cells. MHC – I molecule are found on surface of all nucleated cells.

11. CLASS II MHC HLA – DR, HLA – DQ, HLA – DP  present within HLA – D region Very limited distribution Principally found on the surface of macrophages, monocytes, activated T lymphocytes & B lymphocytes . Primarily responsible for : Graft Vs Host response ; mixed leucocyte reaction. Immune response ( Ir ) gene in mice  Identical to MHC class II ↓ Antigen coded by Ir gene  Ia Antigen (I region associated)

12. STRUCTURE AND FUNCTION – CLASS II α chain and β chain of MHC II - is a membrane bound glycoprotein that contains external domains, a transmembrane segment and a cytoplasmic tail. Functions : To bind peptide antigen and present to CD4 T cells. MHC II are found on surface of antigen presenting cells. CD4 T cells are specific for MHC II Activates B cells for antibody production Plays a significant role in graft versus host response and in mixed in lymphocyte reaction because the immune response gene is identical to MHC II in human

13. CLASS III MHC Complement loci encoded for C2, C4, Factor B and Tumor necrosis factor alpha and beta. Locus  position where a particular gene located in chromosome. Genes encode C2 , C4 complement components of classical pathway. Properdin factor B  alternative pathway

14. CLASS III MHC FUNCTIONS Involved in complement activation. Involved in inflammation caused by cytokines, tumor necrosis factors etc.,

15. CLASS IV MHC Present in T cells of leukemia as well as on immature thymocytes.

16. FUNCTIONS OF MHC MOLECULES MHC molecules contain self as well as non self (foreign) antigen. They bring about defense against infections and diseases. They mediate certain autoimmune disease.