Protective effects of RU 41740, a bacterial immunomodulator, against experimental infections: induction of cytokine and immunoglobulin release in mice after oral administration

Abstract

RU 41740 (Biostim ™) is an immunomodulator extracted from Klebsiella pneumoniae (strain O1:K2). In humans, it is able to reduce the number and duration of infectious exacerbations of chronic bronchitis. Using a mouse model of experimental infection, we found that oral RU 41740 administration strongly protected against gram-negative infections by preventing lethal septicemia, and, to a lesser extent, protected against the gram-positive intracellular pathogen L. monocytogenes. Oral administration of RU 41740 leads to the mobilization of newly dividing T and B cells in the thoracic duct lymph, reflecting the ability of the drug to induce an immune response in gut-associated lymphoid tissue. In cells isolated from mesenteric lymph nodes and spleen, RU 41740 leads to preferential release of the proinflammatory cytokines interleukin (IL)-12 and/or interferon (IFN)-γ, as well as IL-10, a cytokine involved in inhibiting the synthesis of these latter cytokines. RU 41740 also increases the serum total immunoglobulin (Ig)M concentration and elicits IgM and IgG antibodies against the drug. Infection of mice with Klebsiella pneumoniae has similar functional consequences. Pretreatment of infected mice with RU 41740 leads to a fall in the high levels of proinflammatory cytokines (which could be detrimental), and to an increase in IgG antibodies (which are protective).