Diagnosis of Lyme borreliosis: non-specific serological reactions with Borrelia burgdorferi sonicate antigen caused by IgG2 antibodies.

Summary ELISA methods that measure IgG class antibodies to sonicated Borrelia burgdorferi may give false positive results. These errors could be traced to non-specific reactivity in subclass IgG2 in several instances. Sera were sampled randomly from two adult populations, which differed in having a high and low incidence of Lyme disease. If the binding of IgG2 subclass antibodies was left unrecorded in the test by the use of monoclonal reagent antibodies selective for IgGl and IgG3, the frequency of positivity in the ELISA test decreased in samples from the low risk group. Twenty-one samples were found to be positive in an immunoblot confirmatory test. Correct prediction of positivity was obtained for 15 sera by ELISA restricted to IgGl plus IgG3, for only four sera by ELISA restricted to IgG2 and for only six sera by IgG subclass non-restricted ELISA. A non-restricted ELISA with purified flagella of B. burgdorferi as the antigen predicted correctly 14 of the immunoblot-positive sera. The results of this ELISA correlated well with those of the IgGl plus IgG3 subclass restricted ELISA in the high risk population (r = 0·95, prevalence of seropositivity 12%), but was significantly worse for the low risk group (r = 0·47, prevalence 2·9%). IgG subclass restriction also decreased cross-reactions of syphilitic sera in the ELISA with sonicated antigen.