TNF-Mediated Cytotoxicity

Bergmann, S., Shatrov, V., Ratter, F., Schiemann, S., Schulze-Osthoff, K., and Lehmann, V., 1994, Adenosine and homocysteine together enhance TNF-mediated cytotoxicity but do not alter activation of nuclear factor-icB in L929 cells,/. Immunol. 153 1736-1743. 

Tumour necrosis factor (TNF) is selectively cytotoxic for some tumour cells in vivo and in vitro. Fast et al. (1992) determined whether TNF-mediated cytotoxicity for TNF-sensitive tumour targets was related to TNF-stimulated production of NO by the tumour cell itself. They found that a cell line that was sensitive to TNF-mediated cytotoxicity produced NO in response to TNF as measured by the accumulation of nitrite in the supernatants of TNF-stimulated cells. Production of NO in response to TNF was inhibited by N -monomethyl-L-arginine. The kinetics of NO production in response to TNF indicated that most of the NO was produced during the first 24 h and peaked after 48 h of culture and that TNF-stimulated NO production was dose-dependent. TNF-resistant cell lines produced less NO than a TNF-sensitive cell line, and the amount of nitrite produced correlated with the relative sensitivity of each cell line to TNF-mediated cytotoxicity. Recombinant interferon-y augmented the amount of NO produced in response to TNF by both sensitive and resistant cells and correspondingly enhanced the susceptibility of resistant cells to TNF cytotoxicity. 

It appears that TNF-R55 is capable of mediating most TNF activities, whereas the biological activities induced via the TNF-R75 receptor are more limited. For example, TNF s cytotoxic activity, as well as its ability to induce synthesis of various cytokines and prostaglandins, is all mediated mainly/exclusively by TNF-R55. TNF-R75 appears to play a more prominent role in the induction of synthesis of T-lymphocytes. All of the biological activities mediated by TNF-R75 can also be triggered via TNF-R55, and usually at much lower densities of receptors. TNF-R75 thus appears to play more of an accessory role, mainly to enhance effects mediated via TNF-R55. 

Complement-mediated cytotoxicity of cells expressing membrane-bound TNF Yes Yes No... 

Weiss, T., Grell, M., Hessabi, B., Bourteele, S., Muller, G., Scheurich, P., and Wajant, H. (1997). Enhancement of TNF receptor p60-mediated cytotoxicity by TNF receptor p80 Requirement of the TNF receptor-associated factor-2 binding site./. Immunol. 158, 2398-2404. 

Extracts and isolated constituents of P. sidoides were investigated for their effects on nonspecific immune functions in various bioassays 98,107,127). Results imply indirect activity, possibly through activation of macrophage functions. Activation was confirmed through the presence of tumour necrosis factor (TNF-alpha) and inorganic nitric oxides (iNOS). TNF-indncing potencies for EPs 7630 as well as interferon-like activities were also observed 128,129). Interferon (IFN)-beta prodnction increased and natural killer cell mediated cytotoxicity was enhanced in MG-63 hnman osteosarcoma cells pieincubated with Umckaloabo 130). 

Infliximab was designed specihcally to target TNF-a. It also may have more complex actions. Etaneracept, another anti-TNF-a therapy that uses a circulating receptor to clear soluble TNF-a, blocks its biologic effects but is ineffective in Crohn s disease. Infliximab binds membrane-bound TNF-a and may cause lysis of these cells by anti-body-dependent or cell-mediated cytotoxicity. Thus, infliximab may deplete specific populations of subepithelial inflammatory cells. These effects, together with its mean terminal plasma half-life of 8 to 10 days, may explain the prolonged clinical effects of infliximab. 

GZ (23) is known to decrease elevated plasma levels of AST and ALT in various liver diseases. Thus it has been widely used for the treatment of chronic liver diseases (chronic viral hepatitis) in Japan for several years [82]. However, the mechanism of its transaminase-lowering action is not fully understood. Some studies suggested that the decrease of transaminase levels by GZ in patients with chronic viral hepatitis is mediated in part by inhibition of immune-mediated cytotoxicity against hepatocytes [83]. GZ (23) was shown to inhibit the cytotoxicity of CTL against antigen-presenting cells and also to suppress TNF-a induced cytotoxicity in the TNF-a sensitive cell line in vitro. A clinical study reported the use of GZ to bring about an improvement of hepatitis after liver transplantation performed for cirrhosis secondary to hepatitis B complicated by a small hepatocellular carcinoma [84],... 

Interleukin-2 Human recombinant lL-2 aldesleukin, proleukin des-alanyl-1, serine-125 human lL-2) differs from native lL-2 in that it is not glycosylated, has no amino terminal Ala, and has an Ser substituted for the Cys at amino acid 125. The potency of the preparation is represented in International Units in a lymphocyte proliferation assay such that 1.1 mg of recombinant lL-2 protein equals 18 million International Units. Aldesleukin has the following in vitro biologic activities of native lL-2 enhancement of lymphocyte proliferation and growth of lL-2-dependent cell lines enhancement of lymphocyte-mediated cytotoxicity and killer cell activity and induction of interferon-7 activity. In vivo administration of aldesleukin in animals produces multiple immunologic effects in a dose-dependent manner. Cellular immunity is profoundly activated with lymphocytosis, eosinophilia, thrombocytopenia, and release of multiple cytokines e.g., TNF-a, lL-1, interferon-7). Aldesleukin is indicated for the treatment of adults with metastatic renal cell carcinoma and melanoma. Administration of aldesleukin has been associated with serious cardiovascular toxicity resulting from capillary leak syndrome, which involves loss of vascular tone and leak of plasma proteins and fluid into the extravascular space. Hypotension, reduced organ perfusion, and death may occur. An increased risk of disseminated infection due to impaired neutrophil function also has been associated with aldesleukin treatment. 

Mechanistic studies performed in our laboratories point to an IFN-y-induced, NO-dependent, microglial cell-mediated cytotoxicity of oligodendrocytes. The killing is up-regulated by TNF and inhibitable by TGF-j8 (reviewed by Merrill and Murphy, 1995). These data suggest that NO may be involved in the oligodendrocyte cell death that occurs in vivo with MS. 

Moreover, a whole arsenal of potentially cytotoxic effector molecules are expressed and are implicated in NK cell-mediated cytotoxicity. Apart from the exocytic granule-based mechanism involving perforin and granzymes, many members of the TNF family such as TNF, TRAIL and FasL, in membrane-bound and secreted versions, seem to be utilized by NK cells for killing of different target cells (Johnsen et al. 1999 Kashii et al. 1999). 

Kasof G, Goyal L, White E (1999) Btf, a novel death-promoting transcriptional repressor that interacts with Bcl-2-related proteins. Mol Cell Biol 19 4390 404 Kayagaki N, Yamaguchi N, Nakayama M, Kawasaki A, Akiba H, Okumura K, Yagita H (1999) Involvement of TNF-related apoptosis-inducing ligand in human CD4 -H T cell-mediated cytotoxicity. J Immunol 162 2639-2647... 

NO also sensitizes tumor cells to TNF-a-mediated cytotoxicity via inhibition of NF-kB activation, as shown with the AD 10 human ovarian carcinoma cells. The sensitivity of ADIO cells to TNF-a was induced by IFN-y and inhibited in the presence of IFN-y by NOS inhibitors IFN-y could be replaced by the NO donor SNAR By reducing the generation of H2O2, NO disrupts NF-kB activation and sensitizes tumor cells to TNF-a-mediated cytotoxicity (Garban and Bonavida 2001 Huang et al. 2005). 

Han Y, He T, Huang DR, Pardo CA, Ransohoff RM (2001) TNF-alpha mediates SDF-1 alpha-induced NF-kappa B activation and cytotoxic effects in primary astrocytes. J Clin Invest 108 425 35... 

In addition to directly eliciting cell chemotaxis and free-radical production, PAF can also induce the release of various inflammatory cytokines, amongst which tumour necrosis factor (TNF) is of particular importance [ 312 ]. We have recently shown that PAF stimulates TNF production from peripheral blood derived monocytes and at picomolar concentrations amplifies lipopoly-saccharide (LPS)-induced TNF production, effects inhibited by various PAF antagonists [313]. PAF also acts synergistically with interferon-y (IFN-y) to increase the monocyte cytotoxicity. Furthermore, PAF can modulate the production of both interleukin 1 and interleukin 2 (IL-1, IL-2) from rat monocytes and lymphocytes, respectively [222, 223], cytokines which in turn elicit the release of other mediators and growth factors. 

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