Corynebacterium pseudodiphteriticum stimulate alveolar macrophages and improve the respiratory humoral immune response

Abstract

Previously, we demonstrated that nasally administered Corynebacterium pseudodiphteriticum 090104 (Cp) or its bacterium-like particles (BLPCp) were able to increase the resistance of mice against bacterial and viral respiratory pathogens. In this work, we evaluated: a) the interaction of Cp and BLPCp with alveolar macrophages (AMs) and b) the ability of Cp and BLPCp to enhance the humoral immune response induced by a commercial vaccine against Streptococcus pneumoniae. In the first set of experiments, Cp or BLPCp were incubated with primary cultures of murine AMs and the phagocytic activity, and the production of cytokines was evaluated. Optical and electron microscopy analysis revealed that both Cp and BLPCp were efficiently phagocyted by AMs. Both treatments were also able to trigger the production of TNF-α, IFN-γ, IL-6 and IL-1β (p<0.05 vs non-stimulated controls) by AMs. In the second set of experiments, 3 weeks-old-Swiss mice were intranasally immunized at days 0, 14 and 28 with 1:100 PBS dilution of the pneumococcal vaccine Prevenar®13 (PCV), Cp+PCV or BLPCp+PCV, using doses of CP and BLPCp of 108 cells or particles/ml. On day 33, samples of bronco-alveolar lavages (BAL) and serum were collected for the study of specific antibodies. In addition, immunized mice were challenged with S. pneumoniae serotypes 6B or 19F (108 UFC/ml PBS) on day 33 and sacrificed on day 35 (day 2 post-infection) to evaluate the resistance to the infection. Both Cp+PCV and BLPCp+PCV groups had higher specific serum IgG and BAL IgA antibodies than PCV control mice (p<0.05). In addition, mice immunized with Cp+PCV or BLPCp+PCV had lower lung pneumococcal cell counts (p<0.05) as well as lower levels of BAL albumin and LDH indicating a reduced alteration of the alveolar-capillary barrier and lower cellular damage than control mice. The results demonstrated that C. pseudodiphteriticum 090104 and its bacterium-like particles are capable to stimulate the respiratory innate immune system serving as adjuvants to potentiate the adaptive humoral immune response. Our study is a step forward in the positioning of this respiratory commensal bacterium as a promising mucosal adjuvant for vaccine formulations aimed to combat respiratory infectious diseases.