Value of specific immunoglobulin a detection by two immunocapture assays in the diagnosis of toxoplasmosis

Abstract

The diagnosis of Toxoplasma gondii infection is currently based on immunological tests, but tests for IgG and IgM antibodies alone are often insufficient to assess the risk of active disease, especially during pregnancy and in immunodeficient subjects. The supplementary diagnostic value of testing for antitoxoplasmic IgA in cases of acute, chronic, congenital and reactivated toxoplasmosis, relative to classical immunological tests, was evaluated using two immunocapture tests, one based on tachyzoite agglutination and the other on an immunoenzymatic complex recognizing the membrane protein P30 of Toxoplasma gondii. A total of 4,541 sera from 395 uninfected subjects, 468 immunized subjects with chronic infection, 117 subjects with acute infection and 403 children, 103 of whom had congenital toxoplasmosis, was tested. Specific IgA tests were negative in the nonimmune population, but tests for this immunoglobulin subtype became positive very rapidly during primary infection, and IgA disappeared more rapidly than IgM. In the children infected in utero, specific IgA was detected more frequently than IgM. In contrast, in a population of HIV-seropositive subjects with clinical toxoplasmosis, tests for IgA were poorly sensitive. The two tests for specific IgA produced similar results, except in the early stages of primary infection, in which immunoenzymatic testing for anti-P30 IgA was less sensitive than the agglutination method.

Clinical Value of Specific Immunoglobulin E Detection by Enzyme-Linked Immunosorbent Assay in Cases of Acquired and Congenital Toxoplasmosis

“…The index fell below the positivity cutoff by day 10 in all these infants but one (patient 384), in whom it remained positive until 2 months of age; it is noteworthy that this child's mother had a particularly high IgE index (Ͼ4). The presence of anti-Toxoplasma IgE in these uninfected infants may correspond to maternal antibodies which, as documented for IgA (6) and IgM (12), may cross the damaged placental barrier; these specific maternal IgE antibodies are readily detectable when the relative nonspecific IgE concentration is very low in newborns. As with IgM and IgA, the presence of IgE at birth must therefore be confirmed on a sample obtained on day 10.…”

“…The method used to measure specific anti-Toxoplasma IgE was developed in our laboratory from a previously described IgM-IgA ELISA technique (6). Briefly, microplate wells (96-well plates; Nunc 469914F16 Maxisorp) were coated with 200 l of anti-ε monoclonal antibody solution (10 g/ml) (ANA B16; 24138; Argène-Biosoft, Varilhes, France,) for 16 h at room temperature (18 to 25°C).…”

“…IgM and IgA antibodies were detected with an immunocapture (IC) method based on revelation with a suspension of T. gondii (ICT-M and ICT-A) (6). The results were expressed as agglutination scores, ranging from 0 to 12.…”

“…However, IgM antibody detection can be due to naturally interfering IgM (15) or to the persistence of IgM for a long time after primary infection. Conversely, the IgM assay can be negative in patients with secondary reactivation or congenital toxoplasmosis (3,6). Although anti-Toxoplasma IgA antibodies are also informative (i.e., no natural IgA), they can persist for Ͼ6 months after infection, making it difficult to determine the precise date of infection in pregnant women (8,9).…”

Detection of IgA and low-avidity IgG antibodies for the diagnosis of recent active toxoplasmosis

“…Many authors have considered parallel testing of specific IgM and IgA valuable in the diagnosis of some recently acquired infections and, with some reservations, in the diagnosis of the infection in the neonate [4,5]. In addition, the problem of IgM persistence can be reduced because specific IgA does not follow the same time course [6].…”