Abstract • 37

Bacterial ribosomes have been widely used as immunostimulants, in the prevention of upper respiratory tract infections. These subcellular structures are suspected to act as antigen carriers, and to trigger specific immune responses in mucosae associated lymphoid tissues (MALT). In order to investigate this hypothesis, the presence of antigen-specific B-cells and plasma cells was determined in blood samples and tonsils from children treated or not with a preparation containing ribosomes from S. pneumoniae, H.influenzae, S. pyogenes and K. pneumoniae. Activated peripheral B-cells were detected in Elispot as specific antibody-producing cells. Indirect immunofluorescence, using bacterial preparations and anti-ribosomal antibodies was used to enumerate antigen-specific antibody producing plasma cells on frozen cut sections from tonsillar tissue. Significantly higher levels of specific B-cells were observed after ribosomal therapy, confirming that oral administration of ribosomal preparations indeed trigger mucosal immune responses. A likely route is via intestinal Peyer's patches and/or solitary nodules, generating specific immune responses resulting in the redistribution of activated specific B-cells in MALT tissues after trafficking in the lymph and peripheral blood. Terminal differentiation in plasma-cells in mucosal areas would then result in the secretion of protective specific antibodies efficient towards bacterial antigens.