Toxoplasmic lymphadenitis--clinical and serologic profile.

OBJECTIVE: To study the serologic profile of several types of test for toxoplasmosis, in order to contribute to the interpretation of antibody kinetics. METHODS: The clinical and serologic features of 120 cases of lymphadenopathy with known time of clinical onset were studied during 18 months postinfection. Antibody kinetics was determined by Sabin-Feldman dye test, complement fixation with light antigen, IgM immunofluorescent antibody test, and IgM immunosorbent agglutination assay (IgM-ISAGA). Cell-mediated immunity was evaluated by the toxoplasmin skin test. RESULTS: Seventy-five female patients aged 11-54 years (median 27 years) and 45 male patients aged 3-59 years (median 17 years) were studied, 85% of whom were under 30 years of age. Cervical lymph nodes were involved throughout, generally on both sides, with more than one affected ganglion group in 88%. The predominant symptom was asthenia (69%), which persisted in some cases for several months. A negative Sabin-Feldman dye test in a lymphadenopathy with more than three weeks' evolution excludes a toxoplasma etiology. A positive Sabin-Feldman dye test with negative IgM-ISAGA almost invariably excludes recent infection. The Sabin-Feldman dye test was positive in 94% of patients with titers higher than 1 : 16 000 within the first three months. The IgM-ISAGA yielded 98% of positive results, of which 94% were high titers. Titers >/= 1 : 160 in the IgM immunofluorescent antibody test and complement fixation were found to be highly indicative of recent infection, since 87% and 91%, respectively, were found within the first three months. A negative skin test plus positive serology values indicates recent infection. CONCLUSION: Our results indicate that estimation of time of infection on the basis of serologic results is improved by the simultaneous application of several tests, and correlates closely with the presence of clinical lymphadenitis.

High level of expression of the Toxoplasma gondii-recombinant Rop2 protein in Escherichia coli as a soluble form for optimal use in diagnosis.

The rhoptry 2 protein (Rop2) is an interesting protein of Toxoplasma gondii that is involved in the parasite invasion of host cell, it has three T-cell epitopes and high antigenic value. However, the expression of Rop2 as a recombinant protein in Escherichia coli is not an easy task, showing low levels of expression or degradation and solubility problems. Using a recombinant Rop2(196-561) fused to 6 histidine residues, we showed high levels of expression in bacteria growing in terrific broth. rRop2(196-561) was purified mainly as a soluble product and in high concentrations (approx 1 mg/mL) under native conditions (40 mM imidazol in phosphate buffer). However, after a cycle of freezing-thawing rRop2(196-561) became insoluble. When glycerol was added to 26%, immediately after purification, the protein stayed soluble after cycles of freezing-thawing. Finally, it was demonstrated that under these conditions soluble rRop2(196-561) keeps its diagnostic value in contrast with the insoluble protein.