CD4+ T Lymphocytes Subsets in Early Life: Does Exclusive Breastfeeding Promote Allergy?

Breastfeeding provides ideal nutrition and passive immunization for growing infants, protecting them from potentially fatal infectious diseases. Exclusive breastfeeding is recommended for at least six months and should be continued complementarity for another year. One of the justifications for this recommended practice is the prevention of allergic diseases, which has been controversial for many years. Here we reviewed data regarding breastfeeding practices and hypothesized that exclusive breastfeeding for long periods may affect the availability of helper T lymphocyte 1-polarizing antigens in babies. This fact could favor helper T lymphocyte 2 (TH2) phenotype development and consequently increase the incidences of allergies, although we have found no consistent evidence in the literature supporting or denying that breastfeeding plays a role in allergic diseases. The literature mostly presents inconsistencies and/or methodological issues precluding a final answer to this issue. The development of the adaptive immune system depends on exposure to antigens that elicit the production of specific cytokines and activates T lymphocyte populations. It is believed that a promotion of the TH2 phenotype to the detriment of another lymphocyte subset takes place, although the exact knowledge about when this process begins is still under investigation. Therefore, the recent increase in allergy incidence might be partly explained by breastfeeding practices in the world and by the hypothesis presented here, affecting the baby's immune system development through selective antigen availability.