Our main interest is to understand the balance between beneficial and deleterious functions of tumor necrosis factor (TNF) in vivo. First, we aimed to define functions of TNF produced by distinct cell types. Using Cre-loxP technology, we generated a panel of mice with TNF ablation in distinct types of leukocytes—macrophages and neutrophils (MN-TNF mice), T cells (T-TNF mice), and B cells (B-TNF mice)—and also in lymphoid tissue–inducing cells (LTICs) and enterocytes. We evaluated these mice in several pathophysiological models, such as the toxicity of products from Gram-negative and Gram-positive bacteria, experimental autoimmune hepatitis and arthritis, and resistance to two types of intracellular bacteria: Listeria and Mycobacteria. We found that macrophages and neutrophils are the main source of systemic TNF in response to lipopolysaccaride. However, TNF produced by T cells—not only by macrophages and neutrophils—plays a critical and nonredundant role in host defense. B cell TNF is critical for supporting the organized structure of secondary lymphoid organs, and LTIC-specific TNF is indispensable for the organogenesis of Peyer's patches. In an experimental autoimmune liver pathology model, T-TNF appears to be the inducer of the physiological response, whereas MN-TNF results in hepatotoxicity.
A second aim was to define absolute and relative thresholds for diverse functions of TNF, both beneficial and deleterious. This concept may be important for designing better protocols of anti-TNF therapy, a therapy that is highly effective in autoimmune patients but not free from side effects, including weakening of the host defense. One limitation of using murine models for comparative studies on the efficacy of various TNF blockers used in patients is the lack of response to drugs based on monospecific antibodies against human TNF (such as infliximab). To this end, we generated two types of mice “humanized” for TNF. In the first approach, we used transgenic mice with 40 kb of genomic sequences surrounding the human TNF gene and backcrossed them on a TNF-deficient background. Importantly, in these mice human TNF completely compensated for functions of murine TNF with regard to organization of lymphoid tissues and to host defense. In the second approach, we are generating a mouse knockin of the human TNF gene into the endogenous murine TNF locus. In both types of humanized mouse, we can compare the results of anti-TNF therapy against experimental autoimmune diseases by clinically used drugs such as infliximab, adalimumab, and etanercept. For a given type of therapy, we can evaluate the extent of the loss of host defense, including resistance to acute and chronic tuberculosis infections. In parallel, we are using another model of TNF ablation—mice with an inducible (injectable) TNF ablation based on the Mx1-Cre system. The model allows us to determine residual TNF levels in distinct cell types and physiological compartments. By combining information obtained from all these models, we are hoping to define absolute and relative TNF levels necessary for the factor's diverse functions in the adult organism.
Humanized mice in the heterozygous state will allow us to compare the regulation of biosynthesis of human versus mouse TNF in the same cell and clarify the existing controversies about transcriptional regulation of the TNF gene.
Our research is also supported by the Russian Academy of Sciences and the Russian Foundation of Basic Research. Studies on the role of TNF in autoimmunity are performed in collaboration with the German Rheumatism Research Center (Berlin) and supported by a Helmholtz-Humboldt Award. Infection studies are conducted in collaboration with CNRS (Orléans, France) and supported by a European Union Framework Grant.
Last updated October 2008
