Detection of human toxoplasma-specific immunoglobulins A, M, and G with a recombinant Toxoplasma gondii Rop2 protein

The Toxoplasma gondii rhoptry protein Rop2 was expressed in Escherichia call as a fusion protein containing 44 kDa of the 55-kDa mature Rop2, supplied with six histidyl residues at the N-terminal end (Rop2(196-561)). Humoral response during Toxoplasma infection of humans was analyzed by immunoglobulin G (IgG), IgA, and IgM enzyme-linked immunosorbent assay with Rop2(196-561) as the antigen substrate. The analyzed sera were divided according to T. gondii-specific serological tests (IgG, IgA, or IgM indirect immunofluorescence and IgA or IgM immunosorbent agglutination assay) as group A (IgG(+) IgA(-) IgM(-); n = 35), group B (IgG(+) IgA(+) IgM(+); n = 21), group C (IgG(+) IgA(+) IgM(-); n = 5), and group D (IgG(+) IgA(-) IgM(+); n = 16). Twenty-six T. gondii-seronegative sera from individuals with other infections were also included (group E). Anti-Rop2 IgG antibodies were detected in 82.8% of group A sera and in 97.6% of the sera with acute-phase marker immunoglobulins (groups B, C, and D). The percentage of IgA antibody reactivity against Rop2(196-561) was 17.1% in group A, 50% in group D, and 80.8% in groups B and C. The percentage of IgM antibody reactivity was 0% in groups A and C and 62% in groups B and D. Sera from group E failed to show IgA, IgM, or IgG antibody reactivity. Since T. gondii Rop2 elicits a strong humoral response from an early stage of infection, it is suggested that recombinant Rop2(196-561) would be suitable for use in diagnostic systems, in combination with other T. gondii antigens, to detect specific IgG, IgA, and IgM antibodies.