An improved approach to estimate the avidity index of immunoglobulins: Evaluation of the method using IgG anti- Toxoplasma gondii

GARCÍA, VALERIA S.; PEVERENGO, LUZ; PERETTI, LEANDRO E.; GONZÁLEZ, VERÓNICA D.G.; GUGLIOTTA, LUIS M.; DALLA FONTANA, MARIA L.; MARCIPAR, IVÁN S.; LAGIER, CLAUDIA M.

JOURNAL OF IMMUNOLOGICAL METHODS

ELSEVIER SCIENCE BV

Año: 2018

0022-1759

Introduction: Physicians often require elucidating whether a patient is coursing the acute or the chronic stage of an illness, e.g. pregnant women should be diagnosed of acute-toxoplasmosis because their foetuses can suffer severedamage, including death, if not treated. Among serological tests performed for this, the most helpful are: i)identification of specific IgM, and ii) detection of specific IgG with its corresponding avidity index (AI). IgG-AI isestimated by different methods of variable complexity and results not always guarantee a reliable sample characterization. Aim: Evaluating a new, simple method to calculate IgG-AI, to improve sample characterization.Methods: IgG-avidity was assessed by ELISA using rP22a, a recombinant protein recently obtained to be used for acute toxoplasmosis diagnosis. Forty-eight serum samples from pregnant women were characterized by commercialkits. Sixteen samples displayed specific-IgM(+)/IgG(+) with low-AI, 16 had IgM(+)/IgG(+) with high-AI, and 16 displayed specific IgM(-)/IgG(-). IgG-AI was determined by two conventional methods and the new we propose, whichevaluates the area under the avidity curves (AUAC). Results: The highest sensitivity and specificity were obtained with the AUAC method, using rP22a as antigen. The relative dispersion of results, estimated by the coefficient of variation was substantially improved compared with the conventional cutoff-end point method (ca. 10% vs. 34%, respectively; p