Changes in intra vascular complement and antitreponemal antibody titres preceding the Jarisch Herxheimer reaction in secondary syphilis

6 patients with secondary syphilis and one control subject were observed over a period of up to 8 hr following the administration of either penicillin or erythromycin. Serial clinical observations were made and blood samples obtained for complement and serological analysis. The patients showed Jarisch Herxheimer reactions (JHR) of varying intensity which were found to be preceded by and to parallel in degree certain changes in complement and syphilitic antibody titres. Falls in total haemolytic complement, in C4, C3, C6 and C7 and a marked drop in C1INH esterase inhibitor were observed. There was no change in total GBG/GGG or evidence of conversion of GBG to GGG. Associated falls occurred in the titres of the QFTA and QTPHA antibodies but not of the QVDRL or QTPI antibodies. C3 conversion was found in the two patients that suffered severe reactions. Immune complexes were not detected and it is suggested that complement activation occurred in the extravascular body compartment. The significance of these changes in relation to other plasma enzyme systems and to the development of the full clinical picture of the JHR is discussed.