TNF-a-mediated cytotoxicity

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). 

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],... 

TNF- a was first purified from conditioned medium from HL-60 cells. It has a relative molecular mass of 17 kDa when analysed by SDS-PAGE, but 45 kDa when analysed by gel filtration. Thus, the molecule exists as a non-glycosylated trimer with a pi of 5.3. Each monomer comprises 157 amino acids and contains two cysteine residues that form a disulphide bridge. Trimer formation appears to be due to noncovalent interactions between the monomers. Human TNF-a is synthesised as a 233-amino-acid protein that is proteolytically cleaved during processing. Whilst the 17-kDa form is readily secreted (and hence can function as an extracellular mediator), a 26-kDa transmembrane form has also been identified. This form of TNF-a may thus function in cytotoxicity resulting from cell-cell contact. 

Tumor Necrosis Factor There are two types of tumor necrosis factor TNF-a and TNF- 8. Of the two, TNF-a has been studied in more detail. TNF-a is a 157 amino acid polypeptide. It is a mediator of immune regulation, including the activation of macrophages and induction of the proliferation of T cells. Another TNF-a function is its cytotoxic effects on a number of tumor cells. Recent research, however, concentrates on its property in the stimulation of inflammation, particularly in the case of rheumatoid arthritis. Clinical trials are being conducted with drugs to block TNF-a with anti-TNF-a monoclonal antibodies. These antibodies target the excessive levels of TNF-a in the synovial fluid of joints and provide relief to sufferers of rheumatoid arthritis (Exhibit 4.10). 

IL-18 augments T- and NK-cell maturation, cytotoxicity and cytokine production. It stimulates TH differentiation, promotes secretion of TNF-a, IFN-y and GM-CSF and enhances NK cell cytotoxicity by increasing FasL expression. IL-8-mediated neutrophil chemotaxis is promoted by IL-18 via its effects on TNF-a and IFN-y, which are stimulatory in action. It plays an important role in maintaining synovial inflammation and inducing joint destruction in rheumatoid arthritis. In synovium of patients with rheumatoid arthritis, enhanced levels of TNF-a and IL-1 are associated with augmented expression of IL-18. 

Inflammatory mediators in biological fluids (e.g., BAL fluid and serum) can be measured with either bioassays or ELISA. A cytotoxicity bioassay using L929 cells has been used to measure TNF-a in biological fluids collected from rabbits (22). While the availability of rabbit specific reagents can be a limiting factor in the measurement of inflammatory mediators, rabbit specific immunoassays have been described for the chemokines IL-8, GRO, and MCP-1 (23-26). 

Guaianolides (C5 C7 C40L) include many cytotoxic and antineoplastic compounds. Various guaianolides are bitter tasting and insect antifeedants. Zaluzanin inhibits bacterial lipopolysaccharide-induced NFKB-mediated expression of iNOS by immune cells and cynaropicrin inhibits similar induction of TNF-a expression through formation of a covalent protein adduct. Costunolide, 7-hydroxycostunolide and 3,4-epoxydehydroleucodin act in a similar manner to inhibit NFkB binding to DNA. 

Thus, TNF induces a strong prosurvival signal secondary to NFkB activation. This is the main difference between TNF and Fas or TRAIL, which only mediate apoptosis. TNF can have cytotoxic effects, but only when NFkB activation is... 

In the last decade, extensive evidence has gathered suggesting involvement of Kupffer cell-mediated inflammatory reactions in Gin-induced liver injury. It is known that Gin leads to activation of Kupffer cells resulting in secretion of proinflammatory cytokines such as tumor necrosis factor (TNF)-a. Increased levels of TNF-a leads to neutrophilic infiltration and cytotoxicity in the liver. Depletion of both Kupffer cells by glycine and gadolinium chloride and of neutrophils by antineutrophil antibodies protect from... 

The multiplicity of effects of cannabinoids and CBl receptor peculiar distribution led to assume the existence of differentiated receptor sites. In fact, a second different receptor for cannabinoids, called Peripheral Receptor (CX5 or CB2), was cloned. Being present in the spleen and macrophages/monocytes but absent at a central level, said receptor was regarded as responsible for mediating the cannabinoid-induced nonpsychoactive effects (S. Munro et al.. Molecular characterization of a peripheral receptor for cannabinoids. Nature, 365, 61-65,1993). In this regard, the Delta-9-THC ability to induce immunosuppressive effects was proved. Recent experimental results showed that Delta-9-THC can cause alteration in the macrophagic function. In fact, the exposure to Delta-9-THC decreases the cytolytic activity of activated macrophages, measured as TNF-a synthesis, release and cytotoxicity. Moreover, since... 

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. 

II transmembrane protein member of the TNF family (Suda et al., 1993) with an extracellular domain similar to those of TNF-a and TNF-yS. Fas mediates apoptosis when cross-linked with either anti-Fas antibody or Fas ligand and, as we shall see below, plays a role in apoptosis of immature thymocytes and peripheral T cells, CTL cytotoxicity and AICD (reviewed in Kisielow and von Boehmer, 1995 Nagata and Golstein, 1995). 

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. 

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