Immunostimulant-induced maturation of monocyte derived dendritic cells in respiratory infection prophylaxis

Background: Immunostimulants were established many years ago to improve the capacity of the immune system to react to exogenous noxae. Immunostimulants can be synthesized in the lab or extracted from bacterial cultures. For example, bacterial lysates have been shown to have a significant effect on the number of infectious episodes, duration of fever and use of antibiotics in patients affected by recurrent respiratory tract infections. The capacity of bacterial lysates to induce the maturation of human monocyte-derived dendritic cells (DCs) has been indicated as the first and fundamental effect focused on the activation of an efficient immune response. Synthetic drugs, used in clinics in the prophylaxis of recurrent respiratory tract infections, have also been described to induce the maturation of DCs. Pidotimod, one of the most representative immunostimulant drugs, has been proposed to induce DC maturation. However, an optimal maturation of DCs is needed to achieve an efficient immune response. Methods: We evaluated the capacity of pidotimod in inducing the maturation of DCs using a prototypic bacterial lysate, Lantigen B, as a control. This maturation was detected using a monocyte-derived DC maturation assay, measured as an increase in the expression of the CD83 and CD86 and the secretion of IL-1β, IL-12 and IL-23, three pivotal cytokines for the activation of an efficient immune response. Results: In the current experimental conditions, 10, 1 and 0.1 μg of pidotimod had no effects on DCs, whilst Lantigen B was able to induce complete maturation of DCs in vitro. Additionally, the same doses of pidotimod used in conjunction with Lantigen B also had no further effect on DC maturation induced by the bacterial lysate. Conclusion: These findings seem to support the concept that bacterial lysates are more effective than other synthetic immunostimulants in inducing an efficient immune response able to affect the incidence and severity of airway infections.