Studies of syphilitic antibodies. II. Substances responsible for biological false positive sero-reactions.

It has been generally assumed that the substances responsible for biological false positive (BFP) seroreactions for syphilis are antibodies of the same kind as the syphilitic anti-lipoidal antibodies. However, the available evidence for this view is meagre and mainly circumstantial. It has been observed that in the VDRL test substitution of the cardiolipin in the antigen by certain surface-active substances results in a test system which has nothing to do with syphilis but gives results parallel to those in the tests for C-reactive protein (Tuomioja and Kajanne, 1956; Salo and Tuomioja, 1958). Therefore, every substance reacting with heart extracts need not necessarily be an antibody. Except in the case of transient reactions, it is impossible to decide on clinical grounds alone whether the reactions are false positives or whether they mark a latent syphilitic infection. By using a battery of tests it is sometimes possible to draw certain conclusions. Thus, sera reactive with crude alcoholic heart extracts but non-reactive with purified cardiolipin antigens are frequently falsely positive (Olansky, Harris, and Hill, 1953; Loffler, 1959). The introduction of the TPI test formed a rational basis for the study of the persistent BFP reactions. However, there are many cases of old untreated syphilis that are non-reactive in the TPI test, and a considerable proportion of cases thought to be persistent BFP reactors based on a non-reactive TPI test have been positive in the FTA-ABS test (Tuffanelli, Wuepper, Bradford, and Wood, 1967; Lassus, Mustakallio, Aho, and Putkonen, 1967). An additional difficulty in the characterization of substances responsible for the BFP reactions is that their serum titres are usually low. The present report deals with immunochemical and serological properties of anti-lipoidal substances in selected relatively high-titred sera from patients with no clinical or anamnestic evidence of syphilis and with completely negative TPI and FTA-ABS tests. Evidence is sought for association of the substances with the immunoglobulins, and an attempt is made to correlate the serological reaction pattern with the behaviour of the substances in fractionation procedures.