It was seen that when blood from rhesus monkey was injected in rabbits, that resulted in formation of an antibody in the serum of the rabbit which would agglutinate the red cells of the vast majority of the world population (85% and above of the population in an area, depending on the geographic distribution). The group factors involved are termed as rhesus or Rh factors.
Fisher (1951), found three pairs of closely related antigenic factors in the Rh system of human blood, namely, Cc, Dd and Ee, of which’d’ is silent and no antibody against ‘d’ could be made available, but antibody against each of the others are available. On the basis of these antigenic factors, according to Fisher, we have 8 phenotypes with 36 possible genotypes in the Rh system of blood grouping of human blood.
Antibodies for Rh antigens do not occur normally in a man. It never occurs in an Rh +ve person. In Rh -ve subjects, Rh antibody may appear due to Rh +ve transfusion or when a Rh -vemother conceives a child with Rh factors present in the child from the father.
Tests for Rh factor :
Tube technique is followed. When tested for D antigen, anti-D sera in saline and anti-D sera in albumin are used. Clumping is more prominent when anti-D sera in albumin is used. Control tests with known Rh-D +ve and Rh-D -ve cells are done simultaneously in the same process, using same antisera. Incubation for a period of 1 hour at 37°C may be necessary.
Similarly, tests for other Rh factors like Rh C or Rh E etc. may be performed.
Some rare antigenic factors are sometimes allied with the Rh antigens. The followings are well in record —
1. Cw, Cu, Cv and Cx are the alleles of C antigen.
2. Du is an allele of D antigen.
3. G or rg is a complex allele related with adjacent parts of substance of C and D antigens.
4. rM is an allele related to G or rg.
5. rL allele may be related to c and e.
6. Eu and Ew are related to E.
7. hrs is related to e antigen for which antibody is present in some Bantu females.
8. ces or v is related to cDe or cde, a type present in some negroid population.
9. es or Vs is related to v or ces antigen found in negroids.
10. D_ is related to D antigen.
11. Dc _ is related to C, D, c, d,
12. RhA, RhB, RhC, and RhD, all are related to D antigen.