Aqueous humor and serum immunoblotting for immunoglobulin types G, A, M, and E in cases of human ocular toxoplasmosis.

The purpose of this study was to compare the local and systemic Toxoplasma-specific humoral immune responses in individuals with ocular toxoplasmosis (OT). To this end, paired aqueous humor and serum samples from 46 individuals with active OT and from 30 individuals without inflammatory eye disease (controls) were analyzed by immunoblotting for anti-Toxoplasma immunoglobulin G (IgG), IgA, IgM, and IgE directed against 20- to 120-kDa antigens. The presence in the aqueous humor of a unique band, or of at least three bands that were at least three times more intense in aqueous humor than in serum, was taken as evidence of local antibody production. IgG bands were detected in 98% of the aqueous humor samples, while IgA bands were detected in 76%, IgM bands were detected in 8%, and IgE bands were not detected in any. Evidence of local production of specific antibodies was found in 32 cases (70%) (IgG in 23 [50%]; IgA in 16 [35%]). In 10 instances (22%), routine laboratory tests were not indicative of OT. In 14 cases (30%), no local antibody production was detected by immunoblotting; 3 of these cases yielded evidence of local antibody production according to the Goldmann-Witmer coefficient. Local antibody production was revealed for 7 of the 30 controls (23%). Hence, the sensitivity of immunoblotting for IgG and IgA is 70%, and the specificity is 77%. We conclude that immunoblotting for local specific IgG and IgA supports the clinical diagnosis of OT in 70% of cases. In 22% of these, the diagnosis is not confirmed by other laboratory tests. Hence, immunoblotting increases the sensitivity of routine laboratory tests and should be considered for samples that register negative by such tests.