Figure 1.
Paradigm for the proposed biological effects of probiotic bacteria in protection against pneumococcal infection.
Commensal and/or probiotic bacteria can prevent pathogens (pneumococci) from attaching to and colonizing the respiratory epithelium by associating with specific cell surface receptors and by enhancing mucus secretion and the production of secretory IgA. Probiotic bacteria interact with underlying dendritic cells (DCs) which signal to the adaptive immune system to trigger a variety of effector cell types, including Th1, Th2, and Th17 as well as regulatory T cells and B cells depending on the local cytokine/chemokine microenvironment. Furthermore, probiotic bacteria also maintain the epithelial barrier integrity by upregulating the expression of specific tight junction proteins on damaged epithelium as a result of localized inflammatory responses following pathogen (pneumococcal) encounter and invasion. Refer to references [49]–[52] for more detail on probiotic–host effects. Th, T helper cell.