Salivary antibody response to streptococci in preterm and fullterm children: a prospective study

Objectives: Secretory immunoglobulins present in mucosa surfaces represent the first line of defense of the adaptive immune system against infectious challenges. Preterm (PT) neonates' humoral immunity is diminished compared to full-term (FT) newborns. The identification of important antigens (Ags) of virulence of oral species may help in the investigation of the mechanisms of antigenic stimulation and the development of the mucosal immune response. In the present study, we measured saliva levels of immunoglobulins A (IgA) and M (IgM) and characterized the specificity of IgA against Ags of several streptococcal species found early in life.

Methods: This was a prospective observational study. Salivary IgA (sIgA) antibody responses to bacterial species that are prototypes of pioneer (Streptococcus mitis, S. sanguinis, S. gordonii) and pathogenic (Streptococcus mutans) microorganisms of the oral cavity were studied in FT and PT children in two visits: at birth (T0) and at 3 months of age (T3). Salivas from 123 infants (72 FT and 51 PT) were collected during the first 10h after birth (T0) and again at 3 months of age (T3). Salivary levels of IgA and IgM antibodies were analysed by enzyme-linked immunosorbent assay (ELISA). A subgroup of 26 FT and 24 PT children were compared with respect to patterns of antibody specificities against different streptococci Ags using Western blot assays.

Results: No significant differences (P>0.05) in salivary levels of IgA and IgM between FT and PT babies were found at birth. At T3, mean sIgA values were similar between groups and sIgM levels were significantly higher in PT than FT (P<0.05). Western blot assays identified positive IgA response to streptococci in the majority of children, especially in the FT group. There were some differences between groups in relation to the frequency of children with positive response to Ags and intensity of IgA response. In general, oral streptococci Ags were more frequently detected and bands were more intense in FT than in PT, especially in T3. Prospective analysis of patterns of sIgA against Ags of different streptococcal species revealed an increase in complexity of the sIgA antibody response from the first day of birth (T0) to T3 in PT and FT.

Conclusion: The patterns of sIgA response to streptococci Ags appear to be influenced by the gestational age, which might reflect the level of immunological maturity of the mucosal immune system.