IGG ANTI-JK(A) JK(B) ANTIBODIES ARE UNLIKELY TO FIX COMPLEMENT/

Antibodies in the Kidd blood group system show a great deal of serolog ical variability, are notoriously elusive and hence evoke difficulties in detection. However, they have been regularly reported as causing s evere immediate or delayed haemolytic transfusion reactions and this c linical potential has been largely attributed to their complement bind ing ability. In initial investigations on 43 anti-Jk(a)/Jk(b) sera wit h a range of titres of IgG antibody only a few seemed to fix complemen t, though following repeated tests on 20 of these sera a further five were shown to bind complement, making a total of 12 (27.9%) showing ev idence of complement binding. Twenty-three sera were unavailable for r e-testing. Subsequent tests revealed that only those sera which showed direct agglutination or were positive with an anti-IgM reagent in an indirect antiglobulin test (IAT) fixed complement. Evaluations on the IgG fractions of six selected potent anti-Jk(a) sera failed to reveal any complement-fixing ability although all the original sera bound com plement avidly and contained variable amounts of IgM antibody, some at very low subagglutinating levels. These findings challenge past perce ptions and give cause for reflection on the changing methodologies and strategies which could unduly compromise the detection of these poten tially clinically damaging antibodies.