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MHC

MHC. By. Dr. Emad AbdElhameed Morad. Lecturer of Medical Microbiology and Immunology. Transplantation is grafting tissues from one individual to another or from one place to another in the same individual. The main problem in organ transplantation is the occurrence of graft rejection .

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MHC

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  1. MHC By Dr. Emad AbdElhameed Morad Lecturer of Medical Microbiology and Immunology

  2. Transplantation is grafting tissues from one individual to another or from one place to another in the same individual. • The main problem in organ transplantation is the occurrence of graft rejection. • Graft rejection is due the presence of tissue antigens that differ from one to another, thus stimulating immune response that causes rejection. Dr. Emad AbdElhameed Morad

  3. These tissue antigens are known as human leukocyte antigens (HLA) or major histocompatibility (MHC) antigens. • These antigens are genetically determined by MHC genes which are present on chromosome 6. • There are 3 classes of MHC genes (Class I, II, III). Dr. Emad AbdElhameed Morad

  4. (MHC gene complex) MHC class III MHC class I MHC class II MHC class II MHC class I MHC class III Complement proteins C2, C4 Dr. Emad AbdElhameed Morad

  5. MHC antigens class I Dr. Emad AbdElhameed Morad

  6. Class I antigens are 3 types (HLA-A, HLA-B, HLA-C). • There are about 20 different antigenic types of HLA-A, 50 for HLA-B, 8 for HLA-C. • They are present on all nucleated cells. Dr. Emad AbdElhameed Morad

  7. In virally infected cells, viral antigens are expressed on cell surface in association with class I MHC antigens. • This association activates CD8 T cells that will kill virus infected cells. • This is known as MHC restriction. • Class I antigens are typed by microcytotoxicity assay using host leucocytes, specific antibodies and complement. Dr. Emad AbdElhameed Morad

  8. MHC antigens class II Dr. Emad AbdElhameed Morad

  9. Class II antigens are called HLA-D antigens. • HLA-D includes HLA-DR, HLA-DQ and HLA-DP. • There are about 6 antigenic types for HLA-DP, 9 for HLA-DQ and 20 for HLA-DR. Dr. Emad AbdElhameed Morad

  10. Class II antigens are present only on the surface of antigen presenting cells and activated T cells. • CD4 T helper cells recognize antigens on the surface of APCs only if they are associated with class II antigens (MHC restriction). • Class II antigens can be typed by mixed lymphocyte reaction (MLR). Dr. Emad AbdElhameed Morad

  11. MHC antigens class III • Class III MHC genes are involved in production of complement proteins (C2, C4) • They have no relation with graft rejection. Dr. Emad AbdElhameed Morad

  12. Significance of MHC antigens Dr. Emad AbdElhameed Morad

  13. Transplantation and graft rejection • CD4 T cells + MHC class II • CD8 T cells + MHC class I • Paternity testing • Association with diseases: • SLE is associated with HLA-DR3 • Rheumatoid arthritis + HLA-DR4 Dr. Emad AbdElhameed Morad

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