Immunoregulatory and immunostimulatory responses of bacterial lysates in respiratory infections and asthma.

OBJECTIVE

This review focuses on the current understanding of the molecular mechanisms of bacterial lysates, evidence of an induction of innate immunity, and the interaction with immunoregulators, dendritic cells, and regulatory T cells. Clinical relevance is summarized based on the observed mechanisms of action of bacterial lysates.

DATA SOURCES: Academic Search Complete, CENTRAL, Health Source: Nursing/Academic Edition, MEDLINE, and Cochrane databases.

STUDY SELECTIONS: Three independent researchers focused on primary and secondary end points in systematic reviews, meta-analyses, and randomized controlled trials using bacterial lysates as a verum group or within a subpopulation of larger studies. Interventional and observational studies on novel applications also were included. Preclinical studies included murine models focusing on toll-like receptors (TLRs) and regulatory T cells and on the relation with asthma and respiratory immunity.

RESULTS

Bacterial lysates have been observed to induce synergistic TLR-2/6- and TLR-9-dependent innate immunity. It has positive outcomes in decreasing recurrent respiratory tract infections in childhood and adult chronic obstructive pulmonary disease. This class of immunostimulants shows some evidence of mitigating infection morbidity in children and decreasing the frequency of inflammatory episodes (ie, wheezing exacerbations) in children with asthma. Preclinical studies suggest that regulatory T cells can be induced by bacterial lysates and might attenuate T-helper cell type 2 allergic responses.

CONCLUSION

Although successful prevention against all common respiratory pathogens is not possible, bacterial lysates seem capable of targeting specific immunocompetent cells through pathogen recognition receptor activation. Current challenges include clarifying the duality of immunoregulatory and immunostimulatory responses in children at risk for allergy. Larger clinical trials are required to elicit efficacy in allergy prevention.