NEUTRALIZATION OF KNOPS SYSTEM ANTIBODIES USING SOLUBLE COMPLEMENT RECEPTOR-1

Background: Antibodies of the Knops system have been referred to as no n-neutralizable because they cannot be inhibited with serum, saliva, o r urine. Because the Knops system antigens have been located on comple ment receptor 1 (CR1), the question of whether the antibodies could be neutralized with soluble CR1 (sCR1) produced by recombinant DNA techn iques was studied. Study Design and Methods: First, radiolabeled immun oprecipitation techniques were used to test sCR1 for the expression of the high-incidence Knops system antigens. Then, a total of 45 antibod ies were neutralized with sCR1, including the following: one each of a nti-Cr-a, -Dr(a), Do(b), -Hy, -Ge, -Jr(a), -Sc1, -Jk(a), -Cs-a, and -K p(b); two each of anti-lu(b), -Yt(a), and -JMH; three each of anti-McC (a), -Rg, and -SIa-; and four each of anti-Ch, -Kn(a); -Yk(a), -Kn/McC . In addition, two examples of anti-Kn(a) + K, one example of anti-SIa + K + Fy(a), and one example of anti-Yk(a) + E were tested. The sCR1 was added to each test serum and 6-percent albumin was added to the co ntrol; this was followed by neutralization incubation for 5 minutes at 25 degrees C. The antibody samples were then tested by a low-ionic-st rength solution, anti-human globulin technique. Results: The sCR1 expr essed Kn(a), McC(a), SI,(a) and Yk(a). All Knops system antibodies (n = 22) were neutralized by the sCR1, but none of the other 23 alloantib odies decreased in reactivity. The samples containing antibodies of tw o specificities showed inhibition of the Knops system antibody but not of the second antibody. Conclusion: This neutralization method, in wh ich recombinant protein is used, provides an expedient and definitive method of identifying Knops system antibodies.