Dendritic cells (DC) are potent immunostimulatory cells facilitating antigen transport to lymphoid tissues and providing efficient stimulation of T cells. A series of experimental studies in mice demonstrated that cytotoxic T lymphocytes (CTL) can be efficiently induced by adoptive transfer of antigen-presenting DC. However, the success of DC-based immunotherapeutic treatment of human cancer, for example, is still limited because the details of the regulation and kinetics of the DC-CTL interaction are not yet completely understood. Using a combination of experimental mouse studies, mathematical modeling, and nonlinear parameter estimation, we analyzed the population dynamics of DC-induced CTL responses. The model integrates a predator-prey-type interaction of DC and CTL with the non-linear compartmental dynamics of T cells. We found that T cell receptor avidity, the half-life of DC, and the rate of CTL-mediated DC-elimination are the major control parameters for optimal DC-induced CTL responses. For induction of high avidity CTL, the number of adoptively transferred DC was of minor importance once a minimal threshold of approximately 200 cells per spleen had been reached. Taken together, our study indicates that the availability of high avidity T cells in the recipient in combination with the optimal application regimen is of prime importance for successful DC-based immunotherapy.

Demonstrating in vivo interaction of two important biomolecules and the relevance of the interaction to a biological process have been difficult issues in biomedical research. Here, we report the use of a homology modeling approach to establish the significance of protein interactions in governing the activation of programmed cell death in Caenorhabditis elegans. A protein interaction cascade has been postulated to mediate activation of cell death in nematodes, in which the BH3-domain-containing (Bcl-2 homology region 3) protein EGL-1 binds the cell-death inhibitor CED-9 and induces release of the death-activating protein CED-4 from inhibitory CED-4͞CED-9 complexes. We show here that an unusual gain-offunction mutation in ced-9 (substitution of glycine 169 to glutamate) that results in potent inhibition of most nematode cell deaths impairs the binding of EGL-1 to CED-9 and EGL-1-induced release of CED-4 from CED-4͞CED-9 complexes. Based on a modeled EGL-1͞CED-9 complex structure, we generated second-site compensatory mutations in EGL-1 that partially restore the binding of EGL-1 to CED-9(G169E) and EGL-1-induced release of CED-4 from CED-4͞CED-9(G169E) complexes. Importantly, these mutations also significantly suppress the death-protective activity of CED-9(G169E) in vivo. These results establish that direct physical interaction between EGL-1 and CED-9 is essential for the release of CED-4 and the activation of cell death. The structure-based design of second-site suppressors via homology modeling should be widely applicable for probing important molecular interactions that are implicated in fundamental biological processes. P rogrammed cell death is a tightly regulated cellular process crucial for metazoan development and homeostasis (1, 2). Improper regulation of programmed cell death can lead to a variety of diseases, including cancer and degenerative disorders (3). Genetic analysis of programmed cell death in Caenorhabditis elegans has identified four genes whose activities are essential for proper activation and execution of programmed cell death (4). Three of them promote cell death (ced-3, ced-4, and egl-1), and the fourth, ced-9, protects against cell death (5-7). Importantly, these genes encode proteins that share significant sequence and functional homology with mammalian cell death regulators. EGL-1 is similar to BH3-only pro-apoptotic proteins (7, 8), CED-3 is a member of the aspartate-specific cysteine protease family (caspases) (9, 10), CED-4 is similar to one of the apoptotic protease-activating factors (Apaf-1) (11, 12), and CED-9 is a member of a family of anti-apoptotic proteins first defined by the mammalian Bcl-2 protein (8,13,14). Some of the C. elegans proteins and their mammalian homologues have been shown to be functionally interchangeable (4), indicating that the cell death pathway is evolutionarily conserved.Bcl-2 was first identified as an inhibitor of apoptosis by virtue of its ability to protect against lymphocyte cell death (14-16). Subsequently, a family of Bcl-2-related proteins, ...

Here we present a comprehensive molecular mapping of virus-induced autoimmune B cell responses obtained by serological identification of antigens by recombinant expression cloning analysis. Immunoscreening of cDNA expression libraries of various organs (lung, liver, and spleen) using sera from mice infected with cytopathic (vaccinia virus [VV]) or noncytopathic (lymphocytic choriomeningitis virus [LCMV]) viruses revealed a broad specificity of the elicited autoantibody response. Interestingly, the majority of the identified autoantigens have been previously described as autoantigens in humans. We found that induction of virus-induced autoantibodies of the immunoglobulin G class largely depends on the CD40–CD40L-mediated interaction between T and B cells. Furthermore, antibody titers against a number of autoantigens were comparable to the concomitantly induced antiviral antibody response. Comparison of serum reactivity against a selected panel of autoantigens after infection with VV, LCMV, or vesicular stomatitis virus showed that the different virus infections triggered distinct autoantibody responses, suggesting that virus infections may leave specific “autoantibody fingerprints” in the infected host.