4-1BB signaling breaks the tolerance of maternal CD8+ T cells that are reactive with alloantigens.

4-1BB (CD137, TNFRSF9), a member of the activation-induced tumor necrosis factor receptor family, is a powerful T-cell costimulatory molecule. It generally enhances CD8(+) T responses and even breaks the tolerance of CD8(+) T cells in an antigen-specific manner. In the present study we found that it was expressed in the placentas of pregnant mice and that its expression coincided with that of the immunesuppressive enzyme indoleamine 2,3-dioxygenase (IDO). Therefore, we investigated whether 4-1BB signaling is involved in fetal rejection using agonistic anti-4-1BB mAb and 4-1BB-deficient mice. Treatment with agonistic anti-4-1BB mAb markedly increased the rate of rejection of allogeneic but not syngeneic fetuses, and this was primarily dependent on CD8(+) T cells. Complement component 3 (C3) seemed to be the effector molecule because 4-1BB triggering resulting in accumulation of C3 in the placenta, and this accumulation was also reversed by anti-CD8 mAb treatment. These findings demonstrate that 4-1BB triggering breaks the tolerance of CD8(+) T cells to alloantigens in the placenta. Moreover, triggering 4-1BB protected the pregnant mice from Listeria monocytogenes (LM) infection, but led to rejection of semi-allogeneic fetuses. Therefore, given the cross-recognition of alloantigen by pathogen-reactive CD8(+) T cells, the true function of 4-1BB may be to reverse the hypo-responsiveness of pathogen-reactive CD8(+) T cells in the placenta in cases of infection, even if that risks losing the fetus.

Glucocorticoid-induced tumour necrosis factor receptor family-related receptor signalling exacerbates hapten-induced colitis by CD4+ T cells.

The glucocorticoid-induced tumour necrosis factor receptor family related gene (GITR) has been reported to be expressed on the activated T and CD4(+)CD25(+) regulatory T cells (Treg). Signalling triggered by GITR not only neutralizes the suppressive effect of Treg cells, but also augments activation, proliferation and cytokine production of effector T cells. To test the role of GITR in 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis - a murine model of mucosal inflammation - TNBS-injected Balb/c mice were treated with agonistic anti-GITR monoclonal antibody (mAb). Anti-GITR treatment increased the death rate compared to rat IgG-treated mice. Typically, death occurred within 4 days after the TNBS injection when the mice were treated with anti-GITR. The mice that survived anti-GITR treatment suffered from severe inflammation in their entire intestines. CD4(+) T-depletion protected the mice from colitis; even an anti-GITR effect was not apparent. In contrast, CD8(+) T depletion showed less protective than did CD4(+) T depletion. Stimulation of GITR enhanced the production of proinflammatory cytokines including interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-12. It also enhanced the humoral response such as serum levels of IgG(2b) and IgA, which was completely dependent on CD4(+) T cells. Taken together, this study demonstrated that GITR signalling on CD4(+) T cells is involved in the development and progress of colitis by enhancing both T helper type 1 (Th1) and Th2 type responses.

4-1BB (CD137) is required for rapid clearance of Listeria monocytogenes infection.

4-1BB (CD137), a member of the tumor necrosis factor receptor superfamily, is a T-cell-costimulatory receptor that is expressed on activated T cells, dendritic cells, and NK cells. Little has been reported about its role in early host defense against bacterial infection. In this study, we report that 4-1BB-deficient (4-1BB(-/-)) mice are much more susceptible to Listeria monocytogenes (intracellular bacteria) infections than wild-type mice. Upon L. monocytogenes infection, 4-1BB(-/-) mice showed a lower survival rate, a higher bacterial burden in organs, and larger hepatic microabscesses than 4-1BB(+/+) mice. 4-1BB(-/-) mice also had impairment in clearance of bacteria from the bloodstream. Neutrophils from 4-1BB(+/+) mice constitutively expressed 4-1BB, which could be activated to induce intracellular Ca(2+) influx by ligation with anti-4-1BB antibody. On the other hand, neutrophils from 4-1BB(-/-) mice were defective in reactive oxygen species generation, phagocytic activities, and intracellular Ca(2+) mobilization. In addition, mice pretreated with anti-4-1BB monoclonal antibody were much more resistant to L. monocytogenes infection than control antibody-treated mice. Our results support the notion that 4-1BB may play a major role in host defense against intracellular pathogens through neutrophil activation.

4-1BB-mediated immunotherapy of rheumatoid arthritis.

Collagen type II-induced arthritis is a CD4(+) T-cell-dependent chronic inflammation in susceptible DBA/1 mice and represents an animal model of human rheumatoid arthritis. We found that development of this condition, and even established disease, are inhibited by an agonistic anti-4-1BB monoclonal antibody. Anti-4-1BB suppressed serum antibodies to collagen type II and CD4(+) T-cell recall responses to collagen type II. Crosslinking of 4-1BB evoked an antigen-specific, active suppression mechanism that differed from the results of blocking the interaction between 4-1BB and its ligand, 4-1BBL. Anti-4-1BB monoclonal antibodies induced massive, antigen-dependent clonal expansion of CD11c(+)CD8(+) T cells and accumulation of indoleamine 2,3-dioxygenase in CD11b(+) monocytes and CD11c(+) dendritic cells. Both anti-interferon-gamma and 1-methyltryptophan, a pharmacological inhibitor of indoleamine 2,3-dioxygenase, reversed the anti-4-1BB effect. We conclude that the suppression of collagen-induced arthritis was caused by an expansion of new CD11c(+)CD8(+) T cells, and that interferon-gamma produced by these cells suppresses antigen-specific CD4(+) T cells through an indoleamine 2,3-dioxygenase-dependent mechanism.