Cytokines are important mediators of intracranial inflammation following traumatic brain injury (TBI). In the present study, the neurological impairment and mortality, blood-brain barrier (BBB) function, intracranial polymorphonuclear leukocyte (PMN) accumulation, and posttraumatic neuronal cell death were monitored in mice lacking the genes for tumor necrosis factor (TNF)/lymphotoxin-alpha (LT-alpha) (TNF/LT-alpha-/-) and interleukin-6 (IL-6) and in wild-type (WT) littermates subjected to experimental closed head injury (total n = 107). The posttraumatic mortality was significantly increased in TNF/LT-alpha-/- mice (40%; P < 0.02) compared with WT animals (10%). The IL-6-/- mice also showed a higher mortality (17%) than their WT littermates (5.6%), but the difference was not statistically significant (P > 0.05). The neurological severity score was similar among all groups from 1 to 72 hours after trauma, whereas at 7 days, the TNF/LT-alpha-/- mice showed a tendency toward better neurological recovery than their WT littermates. Interestingly, neither the degree of BBB dysfunction nor the number of infiltrating PMNs in the injured hemisphere was different between WT and cytokine-deficient mice. Furthermore, the analysis of brain sections by in situ DNA nick end labeling (TUNEL histochemistry) at 24 hours and 7 days after head injury revealed a similar extent of posttraumatic intracranial cell death in all animals. These results show that the pathophysiological sequelae of TBI are not significantly altered in mice lacking the genes for the proinflammatory cytokines TNF, LT-alpha, and IL-6. Nevertheless, the increased posttraumatic mortality in TNF/LT-alpha-deficient mice suggests a protective effect of these cytokines by mechanisms that have not been elucidated yet.

To investigate the roles of tumor necrosis factor (TNF) and lymphotoxin (LT)-alpha in the development and function of the immune system, the Tnf and Ltalpha genes were simultaneously inactivated in mice by homologous recombination. These mutant mice are highly susceptible to Listeria monocytogenes infection and resistant to endotoxic shock induced by the combined administration of D-galactosamine (D-GaIN) and lipopolysaccharide (LPS). Their splenic microarchitecture is disorganized, characterized by the loss of the clearly defined marginal zone, ill defined T and B cell areas, and absence of MAdCAM-1 and reduced ICAM-1, VCAM-1 and Mac-1 expression. They are devoid of peripheral lymph nodes and Peyer's patches, and show a strong reduction of IgA+ plasma cells in the intestinal lamina propria. The alymphoplasia is accompanied by a marked B lymphocytosis and reduced basal lg levels. Ig depositions in the renal glomerulus and a strong up-regulation of MHC class I antigen expression on endothelial cells of different tissues are observed. The primary humoral immune response towards sheep red blood cells reveals a defective IgG isotype switch, while that against vesicular stomatitis virus is normal. The cytotoxic T cell responses are attenuated, although still effective, against vaccinia, lymphocytic choriomeningitis virus (LCMV-ARM) and LCMV-WE. In conclusion, the combined inactivation of Tnf and Ltalpha confirms their essential role in the normal development and function of the immune system.

Experimental autoimmune encephalomyelitis (EAE) is induced by immunization with myelin components including myelin oligodendrocyte glycoprotein (MOG). Myelin-specific Th1 cells enter the central nervous system (CNS) via binding of very late antigen 4 (VLA-4) to the endothelial vascular cell adhesion molecule 1 (VCAM-1). In the present study, mice with a homologous disruption of the gene encoding IL-6 are found to be resistant to MOG-induced EAE as evidenced by absence of clinical symptoms, minimal infiltration of CD3+ T cells and monocytes into the CNS and lack of demyelination. The failure to induce EAE in IL-6-/- mice is not due to the absence of priming, since lymphocytes of immunized IL-6-/- mice proliferate in response to MOG and produce pro-inflammatory cytokines including IL-2 and IFN-gamma. However, in MOG-immunized IL-6-/- mice, serum anti-MOG antibody titers were found to be drastically reduced. This observation is unlikely to be responsible for resistance to EAE, because B cell-deficient (microMT) mice proved to be fully susceptible to the disease. A striking difference between MOG-immunized wild-type (wt) and IL-6-/- mice was the expression of endothelial VCAM-1 and ICAM-1, which were dramatically up-regulated in the CNS in wt but not in IL-6-/- mice. Taking into account recent studies on the role of VCAM-1 in the entry of Th1 cells into the CNS, the absence of VCAM-1 on endothelial cells in IL-6-/- mice may explain their resistance to EAE.

Background-Interleukin (IL)-6 regulates various aspects of the immune response. In the context of heart diseases, it has been recognized as a prognostic factor for dilated cardiomyopathy, which often results from myocarditis. Methods and Results-Using IL-6 -deficient mice, we studied the role of IL-6 in a model of autoimmune myocarditis resulting from immunization with a peptide derived from cardiac ␣-myosin. Prevalence and severity of myocarditis were markedly reduced in the absence of IL-6. CD4 ϩ T cells from immunized IL-6 -deficient mice proliferated poorly on restimulation with specific antigen in vitro and did not mediate disease on adoptive transfer into IL-6 -competent RAG-2-deficient mice, which otherwise lack B cells and T cells. Production of complement C3, a crucial factor for the development of myocarditis, was strongly upregulated in IL-6 ϩ/ϩ but not in IL-6 -deficient mice after immunization. Conclusions-Our

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The contribution of a transmembrane (Tm) form of TNF to protective immunity against Mycobacterium bovis bacillus Calmette-Guérin (BCG) was studied in transgenic (tg) mice expressing a noncleavable Tm TNF but lacking the TNF/lymphotoxin-α (LT-α) locus (Tm TNF tg mice). These mice were as resistant to BCG infection as wild-type mice, whereas TNF/LT-α−/−, TNF−/−, and LT-α−/− mice succumbed. Tm TNF tg mice developed granulomas of smaller size but at 2- to 4-fold increased frequencies compared with wild-type mice. Granulomas were mainly formed by monocytes and activated macrophages expressing Tm TNF mRNA and accumulating acid phosphatase. NO synthase 2 activation as a key macrophage bactericidal mechanism was low during the acute phase of infection in Tm TNF tg mice but was still sufficient to limit bacterial growth and increased in late infection. While infection with virulent Mycobacterium tuberculosis resulted in very rapid death of TNF/LT-α−/− mice, it also resulted in survival of Tm TNF tg mice which presented an increase in the number of CFU in spleen (5-fold) and lungs (10-fold) as compared with bacterial load of wild-type mice. In conclusion, the Tm form of TNF induces an efficient cell-mediated immunity and total resistance against BCG even in the absence of LT-α and secreted TNF. However, Tm TNF-mediated protection against virulent M. tuberculosis infection can also be efficient but not as strong as in BCG infection, in which cognate cellular interactions may play a more predominant role in providing long-term surveillance and containment of BCG-infected macrophages.

Immunization of mice with myelin components results in experimental autoimmune encephalomyelitis (EAE), which is mediated by myelin-specific CD4+ T cells and anti-myelin antibodies. Tumor necrosis factor α (TNF-α) and lymphotoxin α (LT-α) are thought to be involved in the events leading to inflammatory demyelination in the central nervous system. To ascertain this hypothesis 129 × C57BL/6 mice with an inactivation of the tnf and lta genes (129 × C57BL/6−/−) and SJL/J mice derived from backcrosses of the above mentioned mutant mice (SJL−/−) were immunized with mouse spinal cord homogenate (MSCH) or proteolipid protein. Both 129 × C57BL/6−/− mice and SJL−/− mice developed EAE. In SJL−/− mice immunized with MSCH, a very severe form of EAE with weight loss, paralysis of all four limbs, and lethal outcome was observed. The histologic hallmark was an intense perivascular and parenchymal infiltration with predominantly CD4+ T cells and some CD8+ T cells associated with demyelination in both brain and spinal cord. These results indicate that TNF-α and LT-α are not essential for the development of EAE.

In this review we summarize the essential findings about the function of tumour necrosis factor (TNF) and its cognate receptors TNFR1 and TNFR2, and lymphotoxin alpha (LT-alpha) ligands in immune-mediated CNS inflammation and demyelination. The advent of homologous recombination technology in rodents provides a new method which has been used during the last 5 years and has led to insights into the pathophysiology of experimental autoimmune encephalomyelitis (EAE) in an unprecedented way. Studies with knockout mice in which genes of the TNF ligand/receptor superfamily are not expressed and studies with transgenic mice overexpressing TNF and TNFR reveal the critical role of the TNFR1 signalling pathway in the control of CNS demyelination and inflammation. These studies provide novel findings and at the same time shed light on the complex pathophysiology of EAE. Together, these findings may contribute to better understanding of EAE and open new avenues in experimental therapies for multiple sclerosis.