Contribution of anti-Hsp70.1 IgG antibody levels to the diagnostic certainty of clinically suspected ocular toxoplasmosis

Laboratory diagnosis of ocular toxoplasmosis, the major cause of posterior uveitis worldwide, can be improved. Heat shock protein (Hsp) 70 is involved in cellular infection by Toxoplasma gondii but also in the immune response to this parasite. The authors postulate that infected patients may exhibit serum IgG anti-Hsp70.1 antibodies and that determining the presence of these antibodies could improve the diagnosis of suspected ocular toxoplasmosis. This retrospective case-control study included 26 laboratory-confirmed cases of ocular toxoplasmosis (group A), 41 clinically suspected cases (group B), and 67 currently healthy blood donors who were chronically infected with T. gondii (group C). Laboratory and clinical data were analyzed according to the ocular presentation and Goldmann-Witmer's coefficient. Serum and aqueous humor were sampled at the time of uveitis. Serum anti-Hsp70.1 antibody levels were obtained by ELISA. The probability of ocular toxoplasmosis was estimated by a logistic regression analysis that combined data from serum IgG anti-Hsp70.1 and aqueous-humor IgG anti-T. gondii antibody levels. Serum IgG anti-Hsp70.1 antibody levels were significantly increased in groups A and B when compared to the levels in control group C (P ≤ 0.0034). These levels correlated with the retinal lesion size (r = 0.301; P < 0.0349). Logistic probability and anti-Hsp70.1 antibodies in sera confirmed that 10 of 23 cases in group B were true ocular toxoplasmosis. Anti-Hsp70 may play a role in the immunopathogenesis of ocular Toxoplasma infection. This study showed that the anti-Hsp70.1 antibody and the logistic probability test can confirm clinically suspected ocular toxoplasmosis.