No abstract

Our finding is that the passage of lymphocytes to the lumen is an antigen-dependent event and we also provide direct evidence that M cells are one of the migration routes. Our observations also indicate that lymphoid cells in the intestinal lumen may play an immunologic role in mucosal immunity.

One of the major cell components of the rabbit follicle-associated epithelium is represented by the M cells. M cells are able to harbour variable amounts of immunocompetent cells inside peculiar invaginations of their basolateral cytoplasmic membrane, currently referred to as "pockets." This study provides a description of the exact spatial relationships between the M cells and the cells harboured in these so-called "pockets." Pieces of Peyer's patches, taken from the small intestine of an adult male rabbit, were treated as usual for conventional electron microscopy. Consecutive semithin and ultrathin sections were made through the entire thickness of the follicle-associated epithelium along planes parallel to the mucosal surface. Micrographs, taken from the ultrathin sections, were transposed into a software MacDraw Pro to obtain a computerized three-dimensional reconstruction. Three-dimensional reconstruction of the M cells showed that the "pockets" were not formed by mere invaginations of the cytoplasmic membrane, but that they resulted from the branching of the supranuclear portion of the M cell cytoplasm around the M cell-infiltrating lymphocytes. These intrusive cells could be found inside the "pockets" or lined up with one another, in vertical columns, bordering on the basal aspect of the M cells. The particular arrangement of the M cell apical cytoplasm created a labyrinth within the follicle-associated epithelium, which could be assumed as a real intraepithelial compartment expandable virtually throughout all the epithelium. The functional meaning of the intraepithelial compartment delimited by the M cells and its possible role is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

SUMMARYBALB/c mice injected with lyophilized vaccine from Streptococcus pneumoniae R36a (Pn) predominantly responded with antibody molecules the vast majority of which expressed the public idiotype T15 and were directed to the immunodominant epitope phosphorylcholine (PC). However, after a single immunization with Pn vaccine young (3-month-old) BALB/c mice did not produce any specific anti-T15 antibody response. In contrast, young D1.LP mice were able to mount a specific anti-T15 response upon primary immunization with pneumococcal vaccine. The anti-PC response in the two mouse strains differed in that the proportion of antibody molecules that expressed the T15 idiotype for Pn-primed D1.LP mice showed a smaller proportion of PC-specific antibody expressing the T15 idiotype. Neonatal injection of anti-T15 monoclonal antibodies led to a long-term suppression of the PC-specific T15 B-cell clones but at young/adult age these mice maintained the ability to produce a normal amount of PC-specific antibody. Interestingly, the idiotypically-suppressed BALB/c mice mounted a significant anti-T15 response during the primary response to Pn. We interpreted these data as showing that the level of circulating idiotype may regulate the production of the complementary antiidiotypic antibody. In addition, in vitro experiments demonstrated that the lack of the anti-T15 response during primary antibody response in BALB/c mice is probably because of a state of tolerance that is regulated by T cells.