Naot Y, Barnett E V, Remington J S
J Clin Microbiol. 1981 Jul;14(1):73-8. doi: 10.1128/jcm.14.1.73-78.1981.
In a double-sandwich immunoglobulin M (IgM) enzyme-linked immunosorbent assay recently developed for the detection of IgM antibodies to Toxoplasma, the presence of either rheumatoid factor or antinuclear antibodies did not cause false-positive results. We recently noted, however, that in certain sera containing both rheumatoid factor and antinuclear antibodies, false-positive results do occur. In experiments to define the nature of the cross-reaction, these false-positive results were not found to be a consequence of interactions of the sera with Toxoplasma antigens, but rather were due to interactions of rheumatoid factor-antinuclear antibodies with the Fc portion of IgG antibodies used for the enzyme conjugate. This was avoided when the F(ab')2 fragment of IgG was used for the conjugate. The use of such F(ab')2 conjugates did not affect the sensitivity and, thereby, the usefulness of the double-sandwich IgM enzyme-linked immunosorbent assay for the diagnosis of acute acquired or congenital Toxoplasma infections. We concluded that F(ab')2 fragments of IgG antibodies can be used as enzyme conjugates to avoid false-positive results in sera positive for both rheumatoid factor and antinuclear antibodies in either the conventional test or in our double-sandwich IgM enzyme-linked immunosorbent assay.
在最近开发的用于检测弓形虫IgM抗体的双夹心免疫球蛋白M（IgM）酶联免疫吸附试验中，类风湿因子或抗核抗体的存在不会导致假阳性结果。然而，我们最近注意到，在某些同时含有类风湿因子和抗核抗体的血清中，确实会出现假阳性结果。在确定交叉反应性质的实验中，这些假阳性结果并非血清与弓形虫抗原相互作用的结果，而是类风湿因子-抗核抗体与用于酶结合物的IgG抗体的Fc部分相互作用所致。当使用IgG的F(ab')2片段作为结合物时，这种情况得以避免。使用此类F(ab')2结合物不会影响灵敏度，因此不会影响双夹心IgM酶联免疫吸附试验在诊断急性获得性或先天性弓形虫感染方面的实用性。我们得出结论，IgG抗体的F(ab')2片段可作为酶结合物，以避免在传统试验或我们的双夹心IgM酶联免疫吸附试验中，在类风湿因子和抗核抗体均呈阳性的血清中出现假阳性结果。
