Beveled Slide Style

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.

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).

4
(MHC gene complex)
MHC class III
MHC class I
MHC class II
MHC class I
MHC class II
MHC class III
Complement proteins C2, C4
5

• MHC antigens class I

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.

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.

8

• MHC antigens class II

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.

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).

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.

12

• Significance of MHC antigens

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