Rh factor is an-

RHESUS SYSTEM. The Rhesus (Rh) blood group systemwas first discovered on human red cells by the use of antisera prepared by immunizing rabbits with red cells from a Rhesus monkey. The Rh allelic genes are C or c, D or d, and E or e,located on chromosome 1. One set of 3 genes is inheritedfrom each parent giving rise to various complexcombinations. The corresponding antigens are similarly named Cc, Ee and only D since no d antigen exists. However, out of all these, D antigen is most strongly immunogenic and, therefore, clinically most impoant. In practice, Rh grouping is performed with anti-D antiserum.Individuals who are D-positive are referred to as Rh-positiveand those who lack D antigen are termed Rh-negative.Practically, there are no naturally-occurring Rh antibodies.All Rh antibodies in Rh-negative individuals areacquired from immunization such as by transfusion andduring pregnancy, resulting in fatal hemolytic transfusionreaction and haemolytic disease of the newborn. Ref: Harsh Mohan - Textbook of Pathology, 6th Edition.page no.339