T cell activation causes diarrhea by increasing intestinal permeability and inhibiting epithelial Na+/K+-ATPase.

Inflammatory bowel disease (IBD) is associated with mucosal T cell activation and diarrhea. We found that T cell activation with anti-CD3 mAb induces profound diarrhea in mice. Diarrhea was quantified by intestinal weight-to-length (wt/l) ratios, mucosal Na(+)/K(+)-ATPase activity was determined and ion transport changes were measured in Ussing chambers. Anti-CD3 mAb increased jejunal wt/l ratios by more than 50% at 3 hours, returning to base line after 6 hours. Fluid accumulation was significantly reduced in TNF receptor-1 (TNFR-1(-/-)), but not IFN-gamma knockout mice. Anti-CD3 mAb decreased mucosal Na(+)/K(+)-ATPase activity, which was blocked by anti-TNF mAb and occurred to a lesser degree in TNFR-1(-/-) mice. Neither alpha nor beta subunits of Na(+)/K(+)-ATPase decreased in abundance at 3 hours. Intestinal tissue from anti-CD3-treated mice exhibited increased permeability to mannitol at 1 hour and decreases in electroneutral Na(+) absorption, Na(+)-dependent glucose absorption, and cAMP-stimulated anion secretion at 3 hours. Furthermore, enteral fluid accumulation was observed in CFTR(-/-) mice, indicating a minor role of active anion secretion. These data suggest that diarrhea in IBD is due to TNF-mediated malabsorption rather than to secretory processes. T cell activation induces luminal fluid accumulation by increasing mucosal permeability and reducing epithelial Na(+)/K(+)-ATPase activity leading to decreased intestinal Na(+) and water absorption.

Radiation-induced crypt intestinal epithelial cell apoptosis in vivo involves both caspase-3-dependent and -independent pathways.

Caspases play a major role in virtually all forms of apoptosis. Radiation is well known to induce apoptosis of crypt intestinal epithelial cells (IEC). Here, we examined the role of caspase-3 in radiation-induced IEC apoptosis. We demonstrate that while caspase-3 is present in IEC and activated upon irradiation, IEC in caspase-3-deficient mice partially underwent radiation-induced apoptosis. Typical morphological changes of IEC undergoing radiation-induced apoptosis (ie, blebbing, shrinkage, and nuclear condensation) can occur independently of caspase-3; however DNA fragmentation, as analyzed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining, is mostly, but not entirely, caspase-3-dependent. Overall, these results demonstrate that radiation-induced crypt IEC apoptosis has both caspase-3-independent and -dependent components.

Differential effects of T-cell activation on gastric and small bowel permeability in alcohol-consuming mice.

BACKGROUND: A number of variables influence the effect(s) of alcohol on distinct segments of the intestine. In these studies, we examined the effect of T-cell activation on gastric and small bowel permeability in alcohol-fed mice. METHODS: Gastric permeability was assessed using sucrose absorption, whereas small bowel permeability was followed using the ratio of lactulose to mannitol absorption and inulin absorption. T cells were activated by injecting antigen OVA(323-339) into DO11.10 T-cell receptor transgenic mice. RESULTS: T-cell activation increased gastric and small bowel permeability through a pathway mediated by interferon-gamma and tumor necrosis factor. In mice that were fed a liquid diet that contained 30% ethanol-derived calories for 2 weeks, T-cell activation increased gastric permeability to levels greater than that observed in solid diet or pair-fed, liquid control diet. By comparison, changes in small bowel permeability induced by T-cell activation were abrogated in alcohol-fed mice. Analysis of intestinal cytokine mRNA levels (interferon-gamma and tumor necrosis factor) indicated that relevant mucosal T-cell function was preserved in alcohol-fed mice. CONCLUSIONS: Overall, these data suggest that alcohol potentiates the effects of T-cell activation on gastric permeability, at the same time blunting effects on small bowel permeability

The state of CD4+ T cell activation is a major factor for determining the kinetics and location of T cell responses to oral antigen.

Current models suggest that inductive immune responses to enteric Ag are initiated in Peyer's patches (PP) and mesenteric lymph nodes (MLN) followed by migration of activated, memory-like CD4(+) T cells to extralymphoid sites in the intestinal lamina propria (LP). The resultant immune system contains both naive and activated T cells. To examine the differential responses of naive and memory-like T cells to oral Ag, bone marrow chimeras (BMC) were generated. Irradiated BALB/c hosts were reconstituted with a mix of DO11.10 x RAG-1(-/-) and BALB/c bone marrow. In unprimed DO11.10 and BMC models, LP and PP DO11.10 T cells responded to oral Ag with similar kinetics. Responses of activated, memory-like T cells to oral Ag were examined in thymectomized BMC 60 days after i.p. immunization with OVA peptide in Freund's adjuvant (OVA(323-339)/CFA). Results indicate that i.p. OVA(323-339)/CFA generated a high proportion of memory-like CD45RB(low) DO11.10 T cells in peripheral lymphoid (40%) and intestinal LP (70%) tissue. Previously activated DO11.10 T cells in the LP responded to oral Ag earlier and at 50% higher levels compared with memory CD4(+) T cells localized to PP tissue. These data indicate that responses to oral Ag in antigenically naive animals are initiated in PP whereas in Ag-experienced animals LP T cells respond earlier and more vigorously than cells in PP. Taken together, these data suggest that previous activation alters the hierarchy of T cell responses to oral Ag by enhancing the efficiency of LP T cell activation.

Donor T cell activation initiates small bowel allograft rejection through an IFN-gamma-inducible protein-10-dependent mechanism.

The poor success in controlling small bowel (SB) allograft rejection is partially attributed to the unique immune environment in the donor intestine. We hypothesized that Ag-induced activation of donor-derived T cells contributes to the initiation of SB allograft rejection. To address the role of donor T cell activation in SB transplantation, SB grafts from DO11.10 TCR transgenic mice (BALB/c, H-2L(d+)) were transplanted into BALB/c (isografts), or single class I MHC-mismatched (L(d)-deficient) BALB/c H-2(dm2) (dm2, H-2L(d-)) mutant mice (allografts). Graft survival was followed after injection of control or antigenic OVA(323-339) peptide. Eighty percent of SB allografts developed severe rejection in mice treated with antigenic peptide, whereas <20% of allografts were rejected in mice treated with control peptide (p < 0.05). Isografts survived >30 days regardless of OVA(323-339) administration. Activation of donor T cells increased intragraft expression of proinflammatory cytokine (IFN-gamma) and CXC chemokine IFN-gamma-inducible protein-10 mRNA and enhanced activation and accumulation of host NK and T cells in SB allografts. Treatment of mice with neutralizing anti-IFN-gamma-inducible protein-10 mAb increased SB allograft survival in Ag-treated mice (67%; p < 0.05) and reduced accumulation of host T cells and NK cells in the lamina propria but not mesenteric lymph nodes. These results suggest that activation of donor T cells after SB allotransplantation induces production of a Th1-like profile of cytokines and CXC chemokines that enhance infiltration of host T cells and NK cells in SB allografts. Blocking this pathway may be of therapeutic value in controlling SB allograft rejection.