Published Online: February 15, 2013
The increase of allergic diseases in the industrialized world, and more recently also in lower and middle income countries, has been explained by a decline in infections by different infectious agents, following the observed improvements in hygiene - the so-called “hygiene hypothesis.”
In a recent article in The Journal of Allergy & Clinical Immunology (JACI), Figueiredo et al evaluated a sample of 1,127 children living in urban Brazil. Data on asthma symptoms, environmental exposures, and social conditions were collected using standardized questionnaires. Atopic markers (specific IgE in serum and skin prick test reactivity to aeroallergens) were measured. Cytokines (Th1, Th2, and T regulatory types), messengers responsible for most of the biological effects in the immune system, such as cell mediated immunity and allergic type responses, were measured in peripheral blood leukocytes culture supernatants following stimulation with mitogen. Past and current infections by pathogens (viruses, bacterium, protozoan, and helminths) were assessed by serology and stool examinations. Children were classified as having high or low burden of infections, according to the number of current infections or markers of past infections. A classificatory statistical technique, latent class analysis, was used to identify immune phenotypes based on the production of the different cytokines measured.
The authors demonstrated that children with more educated mothers, living in improved environmental conditions, and with a low burden of infections, were significantly more likely to have a responsive immune phenotype based on the production of generalized Th1, Th2, and Treg cytokines production. In addition to that, the responsive immune phenotype was associated with an increased prevalence of atopic markers but not asthma symptoms.
The authors’ findings might explain how a failure to induce appropriate immune regulation early in life as a consequence of improved environment and lower exposures to pathogens may lead to a higher risk of atopy during childhood and consequently with possible allergic inflammatory illnesses later in life. These findings contribute to a better understanding of the immune mechanisms by which the hygiene hypothesis operates in urban Latin America
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.