Humoral immune response induced by the immunization with recombinant chimeric pneumococcal protein PSPF (PsaA- Spr1875-PspA-FliC) plus heat-killed <i>Lactobacillus rhamnosus</i> CRL1505 in infant mice.

Swiss albino infant mice (3-week old) were immunized by nasal route with PSPF (20 μg in 25 μl of sterile PBS) or PSPF (20 μg) plus heat-killed L. rhamnosus CRL1505 (HK1505) (108 cells) in 25 μl of sterile PBS on days 0, 14 and 28. Five days after the last immunization, serum and broncho-alveolar lavage (BAL) samples were obtained for the determination of specific antibodies. A) Concentration of PSPF-specific IgA and IgG antibodies in BAL. B) Concentration of PSPF-specific IgM, IgG and IgA in serum. Each experimental group consisted of 3 mice per group and experiments were performed in triplicate (n = 9). Results were expressed as mean ± standard deviation. Differences were considered significant at p < 0.05 (*) when compared with animals immunized with PSPF only. Concentrations of specific antibodies in sterile PBS-treated control mice samples were below the detection limit.