Use of the serum reactivity against Toxoplasma gondii excreted-secreted antigens in cerebral toxoplasmosis diagnosis in human immunodeficiency virus-infected patients.

Despite the development of serological and molecular methods in recent years, the diagnosis of cerebral toxoplasmosis in human immunodeficiency virus (HIV)-infected patients still presents difficulties. In the present study, we investigated whether cerebral toxoplasmosis induced changes in the reactivity of serum toward Toxoplasma gondii excreted-secreted antigens (ESA) in order to develop an assay for evaluating HIV-infected patients with cerebral toxoplasmosis. The antigen selection was based on those produced by tachyzoites, since it is the form of the organism responsible for disseminating the infection, as well as stimulation of the humoral and cellular immune responses. By using an ELISA containing pooled ESA recovered from infected culture supernatants with tachyzoites-RH strain (ESA-ELISA), we found that ESA had a high specificity for sera from patients with cerebral toxoplasmosis. The reactions were compared with an ELISA using crude tachyzoites antigen, widely used in traditional serology. The assays were performed on 293 serum samples separated as follows: 100 sera from patients with cerebral toxoplasmosis and AIDS (symptomatic), 99 sera from individuals with chronic toxoplasmosis (asymptomatic) and 94 sera from healthy individuals without toxoplasmosis (control). The crude tachyzoite antigen in ELISA was able to distinguish both groups of sera with toxoplasmosis, as similar reactivity were observed in sera from patients with cerebral toxoplasmosis and those from chronic individuals. In contrast, ESA-ELISA distinguished sera from symptomatic and asymptomatic individuals (three times more reactive in the former group, 12.6 versus 4.2). The assays were reproducible based on immunoblotting and statistical analysis. These data suggest the utility of ESA-ELISA in the diagnosis of cerebral toxoplasmosis in HIV-infected patients, since it provided clear evidence that anti-ESA antibodies are present principally in patients with active infection. The absence of a significant amount of antibodies distinguished the patients without clinical symptoms of infection.