[Characteristics of recombinant fragments of the protective antigen SPA of epidemic typhus pathogens]

Fragments of a gene for species-specific protective antigen SPA of Rickettsia prowazekii earlier cloned in lambda gt11 were recloned into the in-frame expression vector pQE30. Polypeptides encoded by these fragments were shown to be synthesized in Escherichia coli with a yield of up to 100 micrograms/ml of culture and to be accumulated in the cells as inclusion bodies. The partially purified antigens were used in enzyme immunoassay with the sera of humans convalescing from epidemic typhus, tick-borne rickettsioses, and other infectious diseases. One of two recombinant proteins was shown to react in immunoblotting and ELISA with homologous, but not with heterologous, sera. The immunoreactivities in ELISA of the recombinant antigens and heat-denatured SPA proved to be similar, but substantially lower than that of the native SPA. These data as well as the data of other investigators show that serodiagnostics of epidemic typhus using recombinant antigens remains a problem.