Monoclonal antibodies (mAbs) specific for the murine p55 and p75 tumor necrosis factor (TNF) receptors were produced after immunization of Armenian hamsters with the purified soluble extracellular domains of each receptor protein. Four p55- (55R) and five p75 (TR75)-reactive mAbs immunoprecipitated the appropriate receptor from the surface of L929 cells. None of the mAbs cross-reacted with the other TNF receptor form. The mAbs were functionally characterized by their ability to inhibit ligand binding and influence TNF-dependent L cell cytolytic activity or proliferation of the murine cytolytic T cell clone CT6. One p55-specific mAb, 55R-593, displayed agonist activity, while two other p55-specific mAbs (55R-170 and -176) were found to be TNF antagonists. The fourth mAb (55R-286) had no functional effects on cells. Several antibodies specific for the p75 TNF receptor partially inhibited recombinant murine TNF-alpha-dependent cytolytic activity (60%). Blocking mAbs specific for p75 but not anti-p55 inhibited TNF-mediated proliferation of CT6 T cells. When used in vivo, p55- but not p75-specific mAbs protected mice from lethal endotoxin shock and blocked development of a protective response against Listeria monocytogenes infection. In contrast, both p55 and p75 mAbs individually blocked development of skin necrosis in mice treated with murine TNF-alpha. These data thus demonstrate the utility of the two families of murine TNF receptor-specific mAbs and identify a novel function of the p75 TNF receptor in vivo.

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