Inhibition of Streptococcus pneumoniae adhesion by specific salivary IgA after oral immunisation with a ribosomal immunostimulant.

Oral 'Ribomunyl' has been shown to increase levels of specific salivary IgA. The ability of specific salivary IgA to inhibit the adhesion of Streptococcus pneumoniae to buccal epithelial cells was investigated in vitro using 13 saliva samples from healthy volunteers who received 'Ribomunyl' therapy for 3 weeks. The S. pneumoniae strain contained in 'Ribomunyl' was [3H]thymidine-labelled and pretreated with dilutions of saliva for 1 hour at 37 degrees C. Bacterial adhesion was measured after 2 hours' contact with human oral epidermal cell monolayers at 37 degrees C under CO2. Nonadherent bacteria were washed off, and the residual radio-activity of the monolayers was compared with that of bacteria not pretreated with saliva. A significant decrease (p < 0.05) in S. pneumoniae adhesion was observed with 6 saliva samples with high levels of specific IgA. This decrease was seen at all dilutions from 1/5 to 1/1000. In contrast, no significant modification of adhesion was seen in the 7 saliva samples with unmodified levels of IgA. These data demonstrate that the increase in salivary IgA levels during 'Ribomunyl' therapy was linked with the capacity of saliva samples to specifically and efficiently inhibit adhesion of S. pneumoniae to buccal epithelial cells in vitro.