[Monoclonal human immunoglobulin (IgG lambda) with antiethinylestradiol activity, oral contraceptives, and arterial...

In a 36-year-old woman taking an oral contraceptive containing 50 mug of ethinyloestradiol each day, a pulmonary arterial thrombosis and a monoclonal gammapathia were associated. The monoclonal IgI lambda Mai... was prepared. When purified, this IgG lambda binds ethinyloestradiol with strong affinity (Ka= 2.7 times 10(7)M-1) and also 17-beta-oestradiol with a little less affinity (Ka = 0.4 times 10(7)M-1. For those ligands each IgG lambda Mai... molecule has two sites of same affinity and specificity so that a Scatchard plot of the experimental values gives a straight line. It is likely that the antibody sites of the IgG lambda Mai... are the binding sites. These facts support the hypothesis of an immunological mechanism of the thromboembolic disease which may be induced by oral contraceptives.