Question

How a Graft is accepted or rejected?

Please explain what the terms below mean/are:

•AA + BB

•F1 Hyrid

•AB

•AB can accept graft from both AA or BB

•But AA or BB cannot accept the graft from AB

Answer 1

A Graft is accepted or rejected based on the major histocompatibity complex (MHC) antigen differences in host and donor. The immune response due to graft rejection arises from T-cell immunity which shows very high specificity towards MHC antigens.

When immune system of graft recipient detect antigens as self then, it is accepted otherwise rejected.

In case of blood transfusion, there are four types of blood group namely A, B, AB and O.

A type blood contains A antigen and anti-B antibody. It has genotype either I^AI^A or I^AI^o.

B type blood contains B antigen and anti-A antibody. It has genotype either I^BI^B or I^BI^o.

AB type blood contains both A and B antigen while they lack both anti-A and anti-B antibodies. It has genotype I^AI^B.

O type blood contains neither antigen A nor B, and have both the anti-A antibody and anti-B antibody. It has genotype I^oI^o.

AA + BB represents the cross between two individual blood group (homozygous dominant alleles).

F1 Hybrid represents the the result of cross between two blood groups. For AA + BB, F1 hydride will be AB.

AB represents the F1 hybrid obtained from cross between AA and BB.

Since AB has no antibody against either A or B antigens, it will not show any immune response and graft will be accepted. It already has both A and B antigens present, so they will treat these antigens as their own (self).

AA or BB cannot accept the graft from AB because, AA will generate immune response against B antigen of AB while BB will generate immune response against A antigen.