To assess the participation of the four subclasses of IgG in the humoral response to Echinococcus granulosus infection, we determined total and parasite-specific IgG1, IgG2, IgG3 and IgG4 in sera from 46 patients with hydatid disease using an enzyme-linked immunosorbent assay (ELISA). Parasite-specific IgG subclass antibodies were quantitatively measured by means of standard curves obtained by affinity chromatography. Sera from 35 healthy individuals served as controls. The total component of IgG1, IgG2, and IgG3 showed a slight increase in patients with hydatidosis in comparison to normal control subjects with no significant differences. For the IgG4 subclass, however, a marked elevation was found in the patients group (p = 0.001 by analysis of variance). IgG1 and IgG4 subclasses showed a high anti-echinococcus antibody response, whereas there was a low parasite-specific IgG2 and IgG3 response. Indeed IgG-specific antibodies were found to belong mainly to IgG1 (63%) and to IgG4 (30%) and to a lesser extent to IgG2 (5%) and IgG3 (2%). The percentage of the total serum IgG4 antibodies that were specific for hydatid antigen reached a mean level of 18%, significantly higher than that of any of the other three IgG subclasses (p < 0.001 by Student’s t test). Thus, the continuous antigenic stimulation of hydatidosis may result in an enhanced IgG4 subclass response.

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An evaluation of the use of the histamine release test (HRT) in the diagnosis of human hydatidosis is presented. This technique, which makes it possible to evaluate directly IgE dependent immediate hypersensitivity by measuring the histamine released from leucocytes (basophils) after antigenic challenge, was compared with the detection of serum specific IgE by the radio-allergosorbent test (RAST), and with the determination of serum specific IgE by the enzyme-linked immunosorbent assay (ELISA). Of the 54 patients with hydatidosis, all were positive according to HRT, 42 according to RAST and 47 according to ELISA. No false positive results were obtained by HRT in 43 patients with parasitosis other than hydatidosis, however, of these 43, 10 resulted in false positives according to RAST and five according to ELISA. It is concluded that HRT is more sensitive and more specific than RAST and ELISA.

The application of a new serological method, time-resolved fluoroimmunoassay (TRFIA), is described for the diagnosis of urinary schistosomiasis. A chelate of lanthanides (europium) with a long fluorescent life-time is used as label. The intensity of fluorescence is measured after a delay selected to eliminate almost completely the background fluorescence, which decays rapidly. TRFIA was compared with an established method, enzyme linked immunosorbent assay (ELISA). Using sera from proven cases of Schistosoma haematobium infection, 98.1% of the samples were positive by TRFIA and 86.5% by ELISA. Sera from patients infected with helminths other than schistosomes produced only 1.5% of false positives with TRFIA, compared with 12.3% by ELISA. TRFIA is more sensitive and specific than ELISA.

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