Role of Ia-positive cells in the lymphocyte responses to Yersinia

Changes in small intestinal epithelial expression of MHC class II antigen after terminal ileal resection for Crohn's disease

Aphthous lesions in the neoterminal ileum from patients operated for Crohn's disease are an early sign of recurrence that can be identified during ileocolonoscopy. The origin of these lesions was studied in nine patients treated by terminal ileal resection and right hemicolectomy for complicated Crohn's disease. During surgery the neoterminal ileum was turned inside out, the mucosa was carefully inspected and two large mucosal biopsies were obtained. The same procedure was carried out in seven patients operated for other diseases. Four to six months after surgery endoscopy of the neoterminal ileum was carried out and multiple biopsies were obtained from the neoterminal ileum. Another follow-up colonoscopy with biopsies was carried out one year after the operation. The operative specimens and the per- and postoperative biopsies were submitted to routine microscopy and immuno- and enzyme-histochemistry. None of the Crohn's patients had macroscopic lesions in the neoterminal ileum at operation and only one had microscopic signs of inflammation and a positive section margin. Four-six months after operation all Crohn's patients had active aphthous lesions in a 5-20 cm segment of the neoterminal ileum at endoscopy. Biopsies taken at this time showed microscopic features which were not observed in biopsies from control subjects: an increase of HLA-DR+, ATPase+ dendritic cells in the ileal mucosa and a defective expression of MHC class II antigens by the small intestinal epithelial cells. MHC class II expression by the small intestinal epithelial cells returned towards normal after one year.(ABSTRACT TRUNCATED AT 250 WORDS)

Collaboration of bovine T lymphocytes and macrophages in T-lymphocyte response to Brucella abortus

Brucella abortus-induced bovine macrophage-T-lymphocyte collaboration was studied as a prerequisite for the eventual clearance of this infectious organism. Esterase-positive, peripheral blood monocytes functioned as an adherent antigen-presenting cell population. A dual requirement for expression of bacterial antigens in combination with self major histocompatibility complex class II products was required by adherent cells for the activation of T lymphocytes. Comparison of antigen-presenting cell populations that were either trypsinized or nontrypsinized following B. abortus ingestion substantiated the need for phagocytosis and antigen processing. A monoclonal antibody (H4) directed against major histocompatibility complex class II determinants was able to block or, with complement, to abrogate T-lymphocyte responses. Measurement of both proliferation and interleukin 2 production via [3H]thymidine incorporation confirmed specific activation of an enriched T-lymphocyte population. These results indicate that in vivo-primed T lymphocytes of peripheral blood origin recognize phagocytized bacterial components of the facultative intracellular bacterium B. abortus and may contribute to the removal of the bacteria. Furthermore, bovine peripheral blood-adherent cells function as classic antigen-presenting cells, which suggests that macrophages are capable of processing this bacteria. Therefore, any lymphocyte-mediated dysfunction attributable to B. abortus most likely occurs at some point in the cascade of immune events following initial macrophage-T-lymphocyte collaboration.

Pathogenesis of Yersinia-triggered reactive arthritis: immunological, microbiological and clinical aspects

When a patient develops reactive arthritis after Yersinia enteritis, the following conditions are often fulfilled: the patient is HLA-B27-positive; however, some B27-negative individuals develop severe arthritis and some positives do not, in the initial phase, the diarrhea is milder, the anti-Yersinia antibody response of IgG class is more vigorous and persists longer, the anti-Yersinia antibody response of IgA class is more vigorous and persists much longer, the anti-Yersinia antibodies of IgA1 and IgA2 subclass, those with J-chain and, especially, those with secretory piece are produced more vigorously, indicating local immunostimulation close to the intestinal epithelium, in the early phase, Yersinia-IgM immune complexes are found in the circulation, and the lymphocyte transformation response against not only Yersinia but also against other gram-negative enteric bacteria is weaker. When all these aspects are considered together a strong suspicion arises that the patients who are destined to develop reactive arthritis fail in their first line of defense against the invading organism when contracting a Yersinia enteritis. This may lead to persistence of the microorganism within the body, e.g., in the intestinal epithelium or in the mesenteric lymphoid tissues, maintaining a stimulus for a prolonged--apparently futile and perhaps harmful--antibody production. Finally, the initiating and decisive factor should not be forgotten: the Yersinia. Why and how it triggers the process is at present one of the enigmas of the pathogenesis of reactive arthritis.