Is There a Role for Immunostimulant Bacterial Lysates in the Management of Respiratory Tract Infection?

Abstract

Bacterial Lysates are immunostimulants clinically prescribed for the prevention of respiratory tract infections (RTIs). It has been shown that Bacterial Lysates upregulate the immune system, acting both on innate and adaptive reactions. In fact, there are demonstrations of their efficacy in restoring the integrity and immune function of epithelial barriers, activating ILC3 and dendritic cells with an enhanced Th1 response, and producing serum IgG and serum and salivary IgA specific to the administered bacterial antigens. The activated immune system also protects against other bacteria and viruses due to a trained immunity effect. Most studies show that the number of RTIs and their severity decrease in Bacterial Lysates-pretreated patients, without relevant side effects. The Bacterial Lysates treatment, in addition to reducing the number of RTIs, also prevents the deterioration of the underlying disease (i.e., COPD) induced by repeated infections. Despite these positive data, the most recent meta-analyses evidence the weakness of the studies performed, which are of low quality and have an inadequate number of patients, some of which were non-randomized while others were without a control group or were performed contemporarily in different clinical conditions or with different ages. The high heterogeneity of the studies does not allow us to state Bacterial Lysates' effectiveness in preventing RTIs with sufficient certainty. To completely define their indications, double-blind, placebo-controlled, multicenter, randomized clinical trials should be performed for each product and for each indication. The study population should be adequate for each indication. For this purpose, an adequate run-in phase will be necessary.

Keywords: Bacterial Lysates; COPD; adaptive immune system; asthma; children; elderly; innate immune system; respiratory tract infection.

Figure 1

Bacterial Lysates stimulate epithelial cells and dendritic cells through TLR 2 and 4. DCs become activated and secerning cytokines and chemokines stimulate CD8 and NK cells to proliferate and activate. The interaction of DCs with T lymphocytes induces the proliferation of B cells that maturate to plasma cells secerning immunoglobulins specific for the administered Bacterial Lysate. Polyclonal plasma cells produce Ig against other bacteria and viruses. BL-activated epithelial cells secrete chemokines, cytokines, and β-defensin 1 with antimicrobial activity.