We found that highest levels of antibodies to T. gondii infection in BD and SZ were associated with lowest levels of IgG3 (3.1 ± 1.8, vs 2.6 ± 1.8, p = 0.03) and IgG4 levels (3.1 ± 1.8 vs 2.6 ± 1.8, p = 0.04) as compared to controls. The gene discussed is IGHG3; the disease is Behcet disease.