Turner J. D. auteur aut IRD Faulkner H. auteur aut IRD Kamgno J. auteur aut IRD Kennedy M. W. auteur aut IRD Behnke J. auteur aut IRD Boussinesq M. auteur aut IRD Bradley J. E. auteur aut IRD text journalArticle eng IgG4 has been proposed to act as a 'blocking antibody' due to its ability to compete for the same epitopes as IgE thus preventing IgE-dependent allergic responses. IgG4 and IgE are both elevated in helminth infections and strong anti-parasite IgE responses are associated with resistance to infection. We wished to determine the relationship between anti-parasite IgG4 and IgE and Ascaris lumbricoides infection status. We examined anti-parasite responses, including antibody levels to recombinant Ascaris allergen-1A (rABA-1A), a target of serum IgE in endemic populations. Worm burden was indirectly estimated by measuring parasite egg output in a cross-sectional human population (N = 105). Levels of anti-parasite IgG4 and IgE in patients' plasma were quantified by immunoassay. Global anti-parasite antibody responses did not bear any significant relationships with intensity of Ascaris infection. Individuals who had detectable levels of IgE but not IgG4 to rABA-1A (11%) had lower average levels of infection compared with individuals who produced anti-rABA-1A IgG4 (40%) and sero-negative individuals (49%) (P = 0.008). The ratio of IgG4/IgE in rABA-1A responders positively correlated with intensity of infection (P < 0.025). IgG4 levels positively correlated with infection level in younger children (age 4-11) where average levels of infection were increasing (P = 0.038), whereas allergen specific IgE emerged as a correlate of immunity in older children and adults (age 12-36) where infection levels were decreasing (P = 0.048). Therefore, in a gastrointestinal helminth infection, differential regulation of anti-allergen antibody isotypes relate to infection level. Our results are consistent with the concept that IgG4 antibody can block IgE-mediated immunity and therefore allergic processes in humans. (c) 2005 Elsevier SAS. All rights reserved. specialized IgE IgG4 allergen helminth immunity Th2 7 7-8 990-996 2005 1286-4579 https://www.documentation.ird.fr/hor/PAR00000409 10.1016/j.micinf.2005.03.036 1286-4579 https://www.documentation.ird.fr/hor/PAR00000409 IRD - Base Horizon / Pleins textes 2006-03-29 2017-08-23 PAR00000409 fre