Immunostimulants revisited: focus on the pharmacology of Ribomunyl

Ribomunyl is an immunostimulant that was developed and commercialized in the 1980s in France and has subsequently been made available in a large number of countries. The formulation is composed of proteoglycans from Klebsiella pneumoniae and of ribosomes from four of the most commonly encountered bacterial strains in recurrent respiratory tract infections. While it is obviously difficult to present a thorough summary of all historical data, here we revisit the mode of action of this immunostimulant and present a perspective in the context of the most recent data and hypotheses on the mechanisms of the antibacterial immune responses. We provide various examples of these mechanisms in innate immunity (phagocytosis, cell adhesion, dendritic cell maturation, Toll-like receptors, interferon production, proinflammatory cytokines, activation of natural killer cells), as well as in adaptative immunity (polyclonal activation of T and B cells, specific immunoglobulin A immune response in an integrated view of the mucosal immune system, and T helper type 1/type 2 [Th1/Th2] regulation and balance). The effect of this immunostimulant on anti-infectious responses can be explained, not only by a stimulation of the antibacterial defense directly assumed by innate immunity, but also by a stimulation of the specific (adaptative) immune response related to the activation of dendritic cells, of which the pivotal role in T-cell differentiation is already well known. This supports the potential of bacterial immunostimulants such as Ribomunyl in anti-infective therapy.