Serological Characteristics and General Chemical Nature of the In vitro Exoantigens of T. cruzi

Abstract

Serologic, immunologic, and chemical properties of substances produced during in vitro cultivation of Trypanosoma cruzi were investigated. After cultivation of the organisms, the medium contained an antigen which fixed complement in the presence of homologous antisera and produced detectable circulating antibody when injected into experimental animals. Different serologic patterns were observed in an evaluation of the antigen in parallel complement fixation tests using standard somatic antigens as reference. Chemical analyses of the product indicate that it is a complex substance, possibly a glycoprotein. The findings suggest that exoantigen produced during culture of the organism differs from previously described somatic antigens. Complement fixation tests are the methods of choice for serodiagnosis of Trypanosoma cruzi infection, particularly in cases of chronic infection (Pifano, 1960; Maekelt, 1960). However, the crude somatic antigens of T. cruzi used in the CF tests have been shown to lack specificity (Kelser, 1936; Liem and van Thiel, 1941; Romana and Gil, 1946; Chaffee et al., 1956). Treatment of somatic antigen with benzene and chloroform (de Freitas and Almeida, 1949) increased specificity but resulted in a loss of sensitivity. Recently, Fife and Kent (1960) prepared a purified protein antigen which gave excellent results in diagnostic tests, virtually eliminating cross reactivity except with sera from patients with mucocutaneous leishmaniasis. Development of feasible methods for mass cultivation of T. cruzi within cellulose sacs (Fife and Kent, 1960) made possible studies of an alternative, and previously unexplored T. cruzi antigen source, namely the exoantigens which might be produced during the in vitro cultivation of the parasite. Antigens liberated by parasites maintained in media have been Received for publication 7 August 1964. * From work done by the senior author in partial fulfillment of the M.S. degree at Howard University, Washington, D. C. t This work was presented, in part, at the 1st International Congress of Parasitology, Rome, 21-26 September 1964. previously studied (Sadun and Norman, 1957; Minning et al., 1958; Kagan and OliverGonzalez, 1958; Anderson et al., 1962; Sleeman et al., 1963). In addition, limited chemical analyses of similar products have been performed (Stirewalt, 1959; Stirewalt, 1963; Sleeman et al., 1963). In general, the investigations indicate that the antigenic materials liberated by organisms maintained in vitro are less complex than the somatic antigens, and that similar products liberated in vivo may play an important role in the immunogenic response of the host. The present study was conducted to dedermine whether detectable antigenic substances were produced by T. cruzi during in vitro cultivation and, if so, to study their serologic characteristics and general chemical