Chiara Borghesi

Modifications of the follicle-associated epithelium by short-term exposure to a non-intestinal bacterium

This study was undertaken in order to study the effects of short‐term exposure of the follicle‐associated epithelium (FAE) of rabbit Peyers patches to a non‐intestinal, Gram‐positive bacterium. Isolated ileal loops, each containing one Peyers patch (PP), were stimulated for short periods of time (30 and 60 min) with Streptococcus pneumoniae R36a, a micro‐organism normally not present in the intestinal area. Samples from antigen‐stimulated and control Peyers patches were analysed by light (LM), transmission electron (TEM), and scanning electron microscopy (SEM). Stimulation with living pneumococci induced dramatic changes in FAE architecture and morphology. A massive passage of cells from lymphoid tissue to the FAE was rapidly detectable, accompanied by alterations of the FAE surface, with a marked increase of M‐cell area. Furthermore, TEM analysis revealed that M cells were able to internalize living pneumococci. S. pneumoniae R36a is a valid experimental model for the further study of the unique antigen sampling function which characterizes the highly specialized FAE in Peyers patches.

Autologous anti-idiotypic antibody response is regulated by the level of circulating complementary idiotype.

BALB/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 anti‐idiotypic 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.

Arrangement of the small intestine lymphatic network in the Peyer's patches of the mouse. A light and transmission electron microscopic study

The lymphatic network in Peyers patches has been previously studied by scanning electron microscopy in rabbit and sheep. So far, data on the Peyers patch lymphatic network obtained by light and transmission electron microscopy are still lacking. The present work was carried out on several series of consecutive thick and semithin sections of mouse Peyers patches. Ultrastructural analyses were performed on ultrathin sections by traditional transmission electron microscopy. Lymph vessels were detected in the parafollicular and subfollicular areas of Peyers patches. Two independent lymphatic plexuses, the muscularis mucosae lymphatic plexus and the subfollicular plexus, were identified respectively in the mucosal and submucosal layers. These lymphatic plexuses joined outside the patch, both draining into the submucosal lymphatic network of the small intestine. At the ultrastructural level, the muscularis mucosae lymphatic plexus, and the lymph vessels draining into it, showed a close association with bundles of smooth muscle cells. Numerous nerve fibres were detected in proximity to the lymphatic endothelium and, in some cases, synapse-like neuroendothelial associations were observed. We report here the lymph vessel organization observed in mouse Peyers patches and discuss the meaning of the presence of subendothelial nerve terminals.