Jürg Tschopp 1951–2011

On March 22, the field of Immunology lost one of the great Biochemists of his generation a few months from his 60th birthday. Dr. Jurg Tschopp grew up in Basel in his beloved Switzerland. As a youth, he proved to be a gifted athlete. He was nationally recognized in the decathlon and, naturally, growing up a mere stones-throw from the Alps was a formidable skier. I discovered this—largely to my peril. Several times at many a meeting over the years, I unwisely attempted to follow his lead down one too many “challenging” slopes with sobering effect.Jurg TschoppPhoto courtesy of Universite de Lausanne.View Large Image | View Hi-Res Image | Download PowerPoint SlideOf the many memories of my interactions with Jurg, I recall with genuine affection our jousting in Swiss German with my limited, although colorful, vocabulary of around 20 words, acquired when I was a postdoc in Zurich years earlier. Those discussions were brief but nevertheless memorable. It was always clear to me that Jurg possessed a powerful combination of fearlessness, rigor, and excellence, three characteristics that are central to being a great scientist. Thus, his many contributions throughout a brilliant career came, in a way, as no surprise.Jurg received rigorous training as an undergraduate in chemistry and as a graduate student in biophysics at the renowned Biocentrum of the University of Basel, obtaining his PhD in Biophysics in 1979. Immunology caught his attention, and he decided to perform postdoctoral studies under the mentorship of Dr. H.J. Muller-Eberhard at the Scripps Clinic in La Jolla, CA. There, he did important work, showing that the lytic pore of complement was formed by C9 multimers. He continued in the complement field and in 1982 returned to his position as Assistant Professor at the Institute of Biochemistry at the Institute of Lausanne. During the early period of his work in Switzerland he published extensively and in part shifted his research direction to the nature of the lytic components of cytotoxic T lymphocytes (CTLs). His interests in these involved the study of the so-called granzymes, serine proteases that play a role in the CTL process. He cloned the genes of several granzymes and characterized their encoded proteins isolated from granules from cloned CTLs. This work on granzymes complemented his earlier work, in which he characterized a lytic pore-forming component, perforin, which mediates killing by CTL. Jurg's work was influential in establishing the function of these molecules and in describing the acquisition of these cytolytic granules upon the induction of cytolytic activity in CTL. His work on these cytotoxic molecules was recognized not only in a substantial number of primary research publications in prominent immunologic journals but also in an influential review published in 1990 in the Annual Reviews of Immunology. His interest in this area led naturally to Jurg posing the question of whether perforin was the only pathway toward lysis, or whether other pathways played a role. Addressing this issue, in 1994 he published an important paper in which he showed that cytolytic T cell cytotoxicity is mediated through two lytic pathways, perforin and fas. This paper, published in Nature, established this important point and therefore brought Jurg significant recognition.The importance of fas in cell death led Jurg to develop an interest in apoptosis, and in the course of this he contributed importantly to several aspects of the study of apoptosis. He was a regular invited speaker at essentially all the prominent apoptosis meetings. Jurg published some highly important papers on the regulation of the apoptotic pathway following fas ligation and ligation of other TNF receptor family members. Of these papers, several were outstanding. First, he discovered in 1997 that a viral FLICE inhibitory protein (FLIP) was able to prevent apoptosis mediated through the above-mentioned death receptors. This was an important observation for it suggested first that negative regulatory mechanisms existed and second that pathogens abuse such mechanisms in order to subvert host defense mechanisms. In a natural extension of this work, again in a highly influential paper in 1997, Jurg identified the cellular homolog of the viral protein as cellular or c-FLIP. This paper led to an understanding of this important class of molecules whose functions include inhibition of cell death but, in addition, was shown to play interesting roles in positive signaling mechanisms downstream of death receptors. Specifically, his work in collaboration with Ralph Budd led to the fascinating observation that FLIP played a role in T cell proliferation. They first showed, in 1999, that caspases were required for T cell proliferation and then went on to show that FLIP was able to activate NF-κB and Erk pathways. He extended his work to numerous other death receptor families. Jurg's interest in apoptosis and death receptors led naturally to a focusing of his attention to other members of the TNF family. Using bioinformatics, he identified several new members including BAFF, a novel ligand of this family that stimulates B cell growth. It is now clear that BAFF is one of the most important B cell proliferation and differentiation factors and, like several other molecules he identified, is now a significant clinical target.Perhaps Jurg's greatest contributions were his studies on a family of intracellular innate immune sensors that play a critical role in host defense against infection and in the activation of immunity. First, he defined the pyrin domain, a motif similar in structure to CARD and death domains, which is expressed on a large family of innate immune effector and regulatory proteins. Jurg was a prominent contributor to the cloning of members of both the pyrin domain and the CARD domain families. His landmark contribution in this field was published in 2002 in Molecular Cell, in which he defined a new molecular entity he called the inflammasome. This important complex mediates the signals leading to activation of the pyrin domain—carrying Nod-Like Receptor (NLR) proteins through adaptor molecules such as ASC, which can bind NLRs via its pyrin domain and caspase-1 through its CARD domain, leading to the activation of caspase-1, which in turn proteolytically processes and activates the inflammatory cytokine interleukin-1. This exciting new concept has been confirmed by both targeted mutagenesis in mice as well as the characterization of humans that have mutant forms of these proteins that lead to the spontaneous activation of the inflammasome. Indeed, the recognition of this mechanism of spontaneous IL-1 production led to the now successful therapy of these autoinflammatory diseases by the use of the IL-1 receptor antagonist protein in the clinic.Jurg was inspired by the possibility of making a difference in patients' lives and had the brilliant insight that uric acid crystals activated the NLRP3 inflammasome to cause the production of IL-1 and that blocking this could be used as a basis of therapy in the painful and mechanistically puzzling disease of gout. By his own force of will he convinced his medical colleagues to establish this clinically with dramatic and almost immediate effect.In parallel to these great achievements, he identified other platforms similar in concept to the inflammasomes but that play a role in sensing cellular stresses. One of these, which he has called the PIDDosome, acts as a sensor of genotoxic stress, detecting DNA damage and orchestrating the activation of caspase-2, or alternatively leads to NF-κB activation. Finally, Jurg contributed importantly to the molecular systems that identify viral infection in the cellular cytoplasm by identifying the RIG-I/cardif platform that leads to a triggering of the interferon antiviral response.Jurg authored well over 350 publications, many of which were published in top-line journals. More importantly, he made major discoveries and introduced several critical new concepts to the fields of cell death and innate and adaptive immunity. He was almost single-handedly responsible for the introduction of the inflammasome concept, which dominates much of what we know of the innate recognition of infection, and recently he extended his studies to diseases associated with metabolic stress. His achievements were recognized with many awards, including the Friedrich-Miescher Award, the Max Cloetta Award, the San Salvatore Cancer Award, the European Cell Death Organization Award, and the Louis-Jeantet Prize.Jurg was one of the leading biochemists studying immunobiology of his generation. His science was like his sports play, skillful and elegant, competitive yet scrupulously fair. His work was characterized by the utmost of scientific and ethical standards, and in these competitive times, he stood out as a paragon of fairness coupled with scientific excellence. Jurg was both rigorous in his work and generous with materials that he generated and with acknowledgment of the contributions of others. He will be sorely missed.