By M.D. Fulton Roberts
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Extra info for An Introduction to Human Blood Groups
The other blood-group system, called Lewis, displays a number of interesting features that are not found in other blood groups. It seems that two antigens can be recognised, called Le a and Left, but about 6 per cent, of persons carry neither of these antigens. ; the incidence of Le a is higher in children because children's 64 P AND a LEWIS 65 cells heterozygous for Le are agglutinated but those from adults are not ; this unusual situation has not yet been explained. The most notable feature about the Lewis group is a property t h a t has not been found in any other human blood group, but is known in the J group in cattle and the R group in sheep.
Discussion has treated more fully the reason why anti-A or anti-B is absent from persons who do possess the corresponding antigen. It seems that if the foetal tissues encounter in utero any potentially antigenic substance, that substance comes to be regarded as a natural component of the foetus and hence not " foreign " and not antigenic. It has been suggested that the antibodyforming apparatus in foetal life is learning to recognise, perhaps by codes, the foetal tissues themselves, including the blood-group substances, so that antibodies are not produced by an organism against its own tissues.
An example of such deduction of geno types from family studies is taken from Race and Sanger's book (pp. 19 and 20 of the third edition)—". . in the first family . . it is clear from the blood groups of the two elder children that each of the parents must possess an 0 THE ABO SYSTEM 53 gene. The father, therefore, is of the genotype BO and the mother Α 2 0 . I n the second family the father and the girl twin are of the phenotype Av and without the evidence provided by the genotypes of the mother and the boy twin their genotypes could not have been ascertained.
An Introduction to Human Blood Groups by M.D. Fulton Roberts