SummaryMonoclonal 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-c~-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-c~. 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.

The p55 and p75 tumor necrosis factor receptors are known to mediate their effects on cells through distinct signaling pathways. Under certain circumstances, the two classes of TNF receptors cooperate with each another to produce enhanced cellular responses. The only molecular mechanism proposed thus far to explain this effect is the process of "ligand passing," whereby TNF is concentrated at cell surfaces by binding to p75 and then following dissociation from this receptor class binds with high efficiency to p55. Using the in vivo model of TNF-induced TNF receptor shedding we have uncovered a novel ligand-dependent interaction of the two TNF receptors that occurs upon exposure of cells to TNF. Using TNF receptor-specific monoclonal antibodies that bind TNF receptors in the presence or absence of ligand, we report that TNF induces the formation of heterocomplexes consisting of both p55 and p75 TNF receptors. Whereas immunoprecipitates from untreated or human TNF-treated cells formed with either p55 or p75 TNF receptor-specific monoclonal antibodies contained only the relevant TNF receptor class, anti-p55 or anti-p75 precipitated both receptor types from murine TNF-treated cells. Ligand-induced complex formation was transient, occurred at physiologically relevant concentrations of TNF, and occurred with receptors lacking intracellular domains or that contained irrelevant transmembrane domains. Formation of TNF receptor heterocomplexes may therefore 1) define a novel molecular mechanism of ligand passing and/or 2) contribute to cooperative TNF receptor signaling via the juxtaposition of the intracellular domains of the two receptor classes and the signaling proteins that they recruit. TNF1 interacts with two distinct receptors of M r 55,000 and 75,000, which are independently expressed on cell surfaces (1, 2). The p55 and p75 TNF receptors share 28% homology in their extracellular domains but show no homology in their intracellular domains (3). The TNF receptors belong to a receptor family that displays extracellular domain homology largely through conservation of cysteine-rich repeating sequences and includes the low affinity nerve growth factor receptor, Fas, OX-40, CD30, CD40, and 4BB1 (4).Recent work (5-7) has revealed that the two receptor classes interact with distinct families of cellular proteins through their intracellular domains. These observations have led to the suggestion that the two TNF receptors utilize different signaling mechanisms. The ability of each TNF receptor to signal biologic responses in cells has been extensively studied during the past few years. Engagement of p55 is now known to be both necessary and sufficient to induce a variety of proinflammatory TNF-mediated cellular responses including cytotoxicity (8), induction of inducible nitric-oxide synthase (9) and manganous superoxide dismutase (10), expression of intercellular adhesion molecule 1 (ICAM-1) (11, 12), and anti-viral activity (13). In contrast, p75 appears to effect only a limited number of cellular responses, many of which...

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Sudden unexpected death is typically diagnosed in infants, children, teenagers, and young adults following completion of an autopsy that fails to identify a cause of death or when autopsy suggests a potentially genetic cause of death in an individual less than 40, such as cardiomyopathy or aneurysm. Such deaths may be a result of genetic abnormalities that are unable to be diagnosed by gross or microscopic inspection, but may be detectable by molecular studies. Unfortunately, the ability to perform postmortem genetic testing is frequently hindered by lack of an appropriate specimen following completion of an autopsy. This paper provides recommendations developed by the National Association of Medical Examiners with the assistance of genetic counselors. The recommendations establish procedures to facilitate postmortem genetic testing and DNA banking by health care professionals assisting families who have experienced sudden death in young relatives by clarifying proper sample acquisition and storage. Additionally, recommendations for discussion with surviving family members and test planning are provided. The objective of these recommendations is to ensure that postmortem samples suitable for DNA banking are retained, allowing at risk family members improved detection of potentially treatable genetic diseases.