2.2.3. Antigens
2.2.3.1. PsaA
Mice intranasally immunized with some species of Lactobacillus synthesizing PsaA developed systemic anti-PsaA IgG and IgA responses and displayed reduced pneumococcal colonization upon nasal challenge . The immune responses depended on the amount of PsaA production, which vary in Lactobacillus from 20 to 250 ng/109 cells . L. plantarum and L. helveticus induce significant IgA responses in nasal and bronchial washes and IgG in serum as well as reduced nasal colonization of S. pneumoniae 6B compared with the saline control group. However, when compared with strains carrying the control vector, only the recombinant L. helveticus led to a significant reduction of pneumococcal nasal colonization. Although L. casei does not generate significant antibody responses, it results in reduced colonization compared with the saline group, but not the vector control. These results reflect that LAB strains have different adjuvant properties. The three LAB strains synthesize similar amounts of PsaA (150–250 ng/109 cells). They persist in the mice nasopharynx after inoculation for three days except L. casei . Short persistence with the low level of antigen production is not enough for the stimulation of antibody responses in nasal and systemic sites. Thus, using LAB for a vaccine needs to consider the protein synthesis levels, persistence and intrinsic adjuvant properties of different LAB