Immunoblotting can help the diagnosis of ocular toxoplasmosis

Aims-To determine whether IgG immunoblotting can improve the diagnosis of o cular toxoplasmosis. Methods-Samples of serum were tested from patients with ocular lesions that could be caused by toxoplasmosis. All such samples from Scotland and North ern Ireland are usually referred to the Scottish Toxoplasma Reference Labor atory. From questionnaires filled out by the clinicians, two groups of sera were identified: ocular toxoplasmosis (active and quiescent), n = 54 (grou p 1); and eye disease as a result of other causes, n = 36 (group 2). Contro l groups were made up of sera from patients with no eye disease and a norma l dye test result (less than or equal to 125 IU/ml), n=16 (group 3); and to xoplasma seronegative, cytomegalovirus (CMV) positive, and herpes simplex v irus (HSV) positive sera (group 4), n = 18. Results-Immunoblots with an active pattern could be identified (IgG antibod ies against at least four antigens with molecular weight of 6, 20, 22, 23, 25, and 36 kDa). Significantly more of this pattern was found in group 1 (3 3 of 54; 61.1%) compared with group 2 (nine of 36; 25%) or group 3 (six of 16; 37.5%). Within group 1, significantly more sera with an active pattern had dye test results greater than or equal to 65 IU/ml compared with those without. More sera from patients < 30 years of age were found with the acti ve pattern in group 1 compared with group 2. No group 4 sera had active imm unoblot patterns. Conclusions-The immunoblot result adds more support to the diagnosis of ocu lar toxoplasmosis. In cases where the clinical diagnosis is difficult, immu noblots are particularly indicated; if negative, other causes of eye diseas e should be sought.