The prevalence of allergic disorders may stem from reduced microbial exposure during childhood.
Allergic disorders (rhinitis, asthma, atopic dermatitis) result from a systemic inflammatory reaction
triggered by Th2-cell-mediated immune responses against ‘innocuous’ environmental antigens. Initial
interpretations proposed an immune deviation of allergen-specific responses from a Th1 to a Th2 profile
resulting from reduced production of interleukin-12 and interferons by natural immune cells stimulated
by bacterial products. Both stereotypical and selective responses of innate host cells are invoked by
different microorganisms. Early in an infection, pathogens can therefore imprint their ‘signatures’ on
antigen-presenting cells and subsequent immune responses. This interaction between microorganisms
and enterocytes is important for the controlled production of cytokines and chemokines. Some probiotic
microorganisms can modulate the in vitro expression of pro- and anti-inflammatory cytokines in a straindependent
manner, probably skew the immune response towards Th1 phenotype and play an important
role in allergy prevention.