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

Anti-phospholipid antibodies in syphilis and a thrombotic subset of SLE: distinct profiles of epitope specificity

In a study of connective tissue and infectious disease sera, we have demonstrated IgM and IgG anti-cardiolipin activity, in a solid phase radioimmunoassay, in systemic lupus erythematosus (SLE), rheumatoid arthritis, syphilis and in acute malaria caused by four different species of Plasmodium. The highest values were noted in SLE (IgM anti-cardiolipin P less than 0.005, IgG anti-cardiolipin P less than 0.01), but there was no correlation with anti-dsDNA, rheumatoid factor or VDRL titres in any disease group. Anti-cardiolipin binding was significantly associated with the lupus anticoagulant, thrombocytopenia, spontaneous abortions and thromboses in the SLE patients. Ten SLE sera from this thrombotic subset and 10 syphilitic sera with similar anti-cardiolipin activity, were tested against four phospholipid antigens and showed significantly different anti-phosphatidyl ethanolamine/anti-phosphatidyl serine binding ratios (P less than 0.001). These differences in phospholipid epitope specificity could explain the specificity of the VDRL antigen in syphilis serology, and we discuss a putative role for anti-phosphatidyl serine in the thrombotic diathesis of SLE.

Mitochondrial and other tissue autoantibodies in patients with biological false positive reactions for syphilis

Mitochondrial antibodies (`M' fluorescence) similar to those seen in patients with primary biliary cirrhosis but of low titre and predominantly of IgM class were found in 51% of forty-one patients showing chronic false positive reactions for syphilis, in the absence of detectable liver abnormalities. The pathogenic significance of this association is not understood but the antigen of Wasserman reaction and Venereal Disease Research Laboratory tests, cardiolipin, is situated in close proximity to the distinct lipoprotein reactive in `M' fluorescence, both being components of the mitochondrial inner membranes. Since these two antibodies have a low incidence in the population, it is likely that their association in a highly selected group of patients represents a particular immunological abnormality in the context of the collagenoses. Thus four of the cases presented with unusual neurological features.

The presence of `M' fluorescence in biological false positive reactors was strongly correlated with systemic disease. This test, together with those for antinuclear and other tissue antibodies may prove of help in differentiating unusual variants of connective tissue disorders and in the follow-up of symptomless patients who are liable to develop these diseases in later life.