Demonstration of intraocular synthesis of immunoglobulin G toxoplasma antibodies for specific diagnosis of toxoplasmic chorioretinitis by enzyme immunoassay.

By using a modified enzyme immunoassay we have conducted a detailed study on the intraocular synthesis of toxoplasma antibodies during ocular toxoplasmosis. In control patients operated on for cataracts, the ratio of immunoglobulin G (IgG) toxoplasma antibodies in serum to those in aqueous humor was more than 100. In eight of the nine patients with clinically diagnosed toxoplasmic chorioretinitis, the ratio ranged between 6 and 56. In five patients with some other type of uveitis, the ratio was comparable with that in controls. Parallel determinations of mumps IgG antibody ratios were carried out to prove that the increased intraocular toxoplasma antibody levels were not a result of increased diffusion or polyclonal antibody stimulation. In all patients, mumps antibody ratios were within normal range. We also tested the samples of aqueous humor for IgM and IgA antibodies, but the antibodies in the aqueous humor were found to be exclusively IgG. Our results indicate that IgG-class anti-toxoplasma antibodies are produced locally within the eye in cases of toxoplasmic chorioretinitis. The determination of these antibodies can offer a valuable aid to make a specific etiological diagnosis of ocular toxoplasmosis.