Get Complete Information on the Mouse MHC Complex

MHC Class I

It consists of two major loci, K and D. Unlike the human MHC, the mouse class I gene complex loci are not together but they are separated by class II and class III.

MHC Class II:

The class II gene complex contains two loci A and E, each loci code for one a- and one B- chain polypeptide, to produce one class II molecule. The mouse class II gene complex is also known as the I-region.

Since they determine the magnitude of immune responsiveness of different mouse strains to certain antigens, the genes in this complex are referred as Immune response genes or Ir genes. Products of each loci A and E are termed as IA and IE antigens and collectively they are known as la antigens.

MHC Class III:

The class III gene complex code components of the complement system. MINOR

Histocompatibility

Genetic loci responsible for encoding histocompatibility antigens other than those encoded by the MHC molecules are referred as minor histocompatibility genes. The proteins produced by them are “Minor histocompatibility (mHC) antigens”.

Minor histocompatibility antigens are normal proteins and polymorphic in a given population. Minor histocompatibility antigens or mHAgs are targets of graft-versus-host disease and graft-versus-leukemia responses after allogeneic HLA identical hematopoietic stem cell transplantation.

Hence human minor histocompatibility antigens (mHags) have been recognized as barriers to successful hematopoietic cell transplantation (HCT) from normal donors.

Only a few human minor H antigens have been molecularly characterized and in all cases, amino acid differences between homologous donor and recipient proteins due to nucleotide polymorphisms in the respective genes were responsible for immunogenicity.

Ideal minor histocompatibility antigens would be derived from proteins that are not only selectively expressed on hematopoietic cells, including leukaemia cells, but are also necessary for cell function.

The problems created by the minor histocompatible molecules are less frequent than those of the major histocompatibility complex (MHC).

Several human minor histocompatibility antigens, such as HA-1, HA-2, HB-1 and BCL2A1, are expressed by hematopoietic cells only. They are investigated as potential targets for a graft-versus-leukemia (GVL) effect.

The minor histocompatibility antigen (mHag) HA-1 is the only known mHag for which mismatching is correlated with the development of severe graft versus host disease (GvHD) after human leukocyte antigen-identical bone marrow transplantation.

The location of some of mHC loci on the X and Y chromosomes explains why grafts from males to females may be rejected while grafts from females to males are accepted.

In the mouse roughly 30 minor histocompatibility loci have been recognised, comprising more than 500 genes. Some investigators suggest that there may be nearly 1,000 genes scattered through out the mouse genome.