Bacterium-like obtained from the respiratory commensal bacteria Corynebacterium pseudodiphtheriticum improve the immune response to chimeric pneumococcal antigen

Abstract

Previously, it was demonstrated that the nasal priming of mice with viable and non-viable Corynebacterium pseudodiphtheriticum 090104 (Cp) differentially modulated the respiratory innate immune response against Streptococcus pneumoniae (Sp). The aim of this work was to study whether the nasal immunization with the recombinant chimeric pneumococcal protein PSPF (PsaA-Spr1875-PspA-FliC) and viable Cp (VCp) or bacteria-like particles obtained from Cp (BPCp) are able to induce specific respiratory and systemic immune responses and improve resistance to Sp infection. Swiss-albino mice (6-weeks-old) were nasally primed with PSPF, PSPF+VCp or PSPF+BPCp on days 0, 14 and 28 (20 μg of PSPF, 108 VCp cells or BPCp). Five days after the last immunization, the levels of anti-PSPF IgM, IgG and IgA antibodies in broncho-alveolar lavage (BAL) and serum, and the resistance to pneumococcal infection were determined. The nasal immunization with PSPF induced specific IgM, IgA and IgG antibodies in the serum and BAL, and reduced lung bacterial counts and avoided dissemination of pneumococci into the blood after the challenge with Sp serotypes 6B or 19F. Mice immunized with PSPF+VCp or PSPF+BPCp showed significantly higher levels of respiratory and serum antibodies, and lower counts of serotypes 6B and 19F in lungs than the PSPF group. PSPF+BPCp was more efficient than PSFP+VCp to improve the humoral immunity (p<0.01) and the resistance to pneumococcal infection (p<0.05). Nasal immunization with PSPF together with bacteria-like particles obtained from C. pseudodiphtheriticum 090104 as mucosal adjuvant could be an interesting alternative to improve protection against pneumococcal infection.