Respiratory syncytial virus replication is prolonged by a concomitant allergic response.

Epidemiological studies show an association between early exposure to respiratory syncytial virus (RSV) and the development or exacerbation of asthma. This idea is supported by studies in mice that demonstrate worsened airway hyper-reactivity (AHR) when RSV-infected animals are exposed to allergen. The effect of allergen on RSV disease, however, has not been reported. Cotton rats (Sigmodon hispidus) that have been used as a model to study RSV pathogenesis were sensitized to extracts of Aspergillus fumigatus (Af), a common household mould. The allergic response to Af included eosinophilia, formation of granulomas and induction of Th2 type cytokines. RSV infection prior to allergen challenge resulted in exacerbation of the inflammatory response as well as increased airway responsiveness to methacholine. The exacerbated response was indeed dependent on virus replication. Virus replication in turn was influenced by the allergic response, with persistence in the noses for 2 days longer in animals challenged with allergen. This diminished clearance corresponded to decreased induction of mRNA for IFN-gamma, a Th1-type cytokine that is characteristic of viral infection. Treatment of RSV-infected Af-challenged animals with recombinant IFN-gamma reduced the allergic inflammatory response as well as the relative levels of Th1 and Th2 cytokine mRNA. However, this treatment did not reduce airway reactivity, showing that these pathologic and physiologic measures of exacerbated disease are independent. We speculate that the reciprocal effect of the allergic response on viral immunity may benefit the host by limiting exacerbation of physiologic responses that are IFN-gamma-dependent.

Molecular cloning of ILP-2, a novel member of the inhibitor of apoptosis protein family.

Inhibitor of apoptosis protein (IAP)-like protein-1 (ILP-1) (also known as X-linked IAP [XIAP] and mammalian IAP homolog A [MIHA]) is a potent inhibitor of apoptosis and exerts its effects, at least in part, by the direct association with and inhibition of specific caspases. Here, we describe the molecular cloning and characterization of a human gene related to ILP-1, termed ILP-2. Despite high homology to ILP-1, ILP-2 is encoded by a distinct gene, which in normal tissues is expressed solely in testis. In contrast to ILP-1, overexpression of ILP-2 had no protective effect on apoptosis mediated by Fas (also known as CD95) or tumor necrosis factor. However, ILP-2 potently inhibited apoptosis induced by overexpression of Bax or by coexpression of caspase 9 with Apaf-1, and preincubation of cytosolic extracts with ILP-2 abrogated caspase activation in vitro. A processed form of caspase 9 could be coprecipitated with ILP-2 from cells, suggesting a physical interaction between ILP-2 and caspase 9. Thus, ILP-2 is a novel IAP family member with restricted specificity for caspase 9.

c-IAP1 is cleaved by caspases to produce a proapoptotic C-terminal fragment.

Although human c-IAP1 and c-IAP2 have been reported to possess antiapoptotic activity against a variety of stimuli in several mammalian cell types, we observed that full-length c-IAP1 and c-IAP2 failed to protect cells from apoptosis induced by Bax overexpression, tumor necrosis factor alpha treatment or Sindbis virus infection. However, deletion of the C-terminal RING domains of c-IAP1 and c-IAP2 restored antiapoptotic activity, indicating that this region negatively regulates the antiapoptotic function of the N-terminal BIR domain. This finding is consistent with the observation by others that the spacer region and RING domain of c-IAP1 functions as an E3 ligase, promoting autoubiquitination and degradation of c-IAP1. In addition, we found that c-IAP1 is cleaved during apoptosis to 52- and 35-kDa fragments. Both fragments contain the C-terminal end of c-IAP1 including the RING finger. In vitro cleavage of c-IAP1 with apoptotic cell extracts or with purified recombinant caspase-3 produced similar fragments. Furthermore, transfection of cells with the spacer-RING domain alone suppressed the antiapoptotic function of the N-terminal BIR domain of c-IAP1 and induced apoptosis. Optimal death-inducing activity of the spacer-RING required both the spacer region and the zinc-binding RING domain of c-IAP1 but did not require the caspase recruitment domain located within the spacer region. To the contrary, deletion of the caspase recruitment domain increased proapoptotic activity, apparently by stabilizing the C-terminal fragment.

Differential effects of CD30 activation in anaplastic large cell lymphoma and Hodgkin disease cells.

CD30 is a member of the tumor necrosis factor (TNF) receptor superfamily that is expressed on activated lymphocytes, as well as on neoplastic cells of Hodgkin disease (HD) and anaplastic large cell lymphoma (ALCL). A number of reports have shown that, depending on cellular context, CD30 signaling can exert a variety of effects, ranging from cell death to cellular proliferation. In the present study this disparity was examined, using a number of ALCL- and HD-derived cell lines. Activation of CD30 led to the induction of apoptotic death of ALCL cells, along with the selective reduction of TNF receptor-associated factor 2 and impairment in the ability of these cells to activate the pro-survival transcription factor nuclear factor kappa B (NF-kappa B). In contrast, HD cells, which constitutively express NF-kappa B, were not susceptible to CD30-induced apoptosis but could be sensitized following ectopic overexpression of a superdominant I kappa B. These studies suggest that NF-kappa B plays a determining role in the sensitivity or resistance of lymphoma cells to CD30-induced apoptosis, which may have important consequences in the clinical treatment of CD30-positive neoplasia. (Blood. 2000;96:4307-4312)

The IAP proteins: caspase inhibitors and beyond.

Apoptosis, or programmed cell death, occurs as an outcome of signals that direct cells to perish. Whether initiated by specifically activated receptors or induced through viral infection, apoptosis is an important means by which organisms maintain health and homeostasis. The apoptotic pathway uses several regulatory proteins that prevent uncontrolled cell death, which would be detrimental to the organism. Richter and Duckett review the recently discovered and characterized inhibitors of apoptosis proteins (IAPs). Not surprisingly, IAPs were first identified in viruses that were able to subvert apoptosis in infected cells. Evidence exists suggesting that, in addition to inhibiting apoptosis, IAPs are involved in signal transduction and cell cycle regulation. Richter and Duckett also review other recent observations indicating that some IAPs may have roles in protein ubiquitination. Although the various roles of the IAPs are beginning to be uncovered, new questions arise about the breadth of their functions and the proteins to which IAPs bind.

Selective activation of JNK1 is necessary for the anti-apoptotic activity of hILP.

The balance between the inductive signals and endogenous anti-apoptotic mechanisms determines whether or not programmed cell death occurs. The widely expressed inhibitor of apoptosis gene family includes three closely related mammalian proteins: c-IAP1, c-IAP2, and hILP. The anti-apoptotic properties of these proteins have been linked to caspase inhibition. Here we show that one member of this group, hILP, inhibits interleukin-1beta-converting enzyme-induced apoptosis via a mechanism dependent on the selective activation of c-Jun N-terminal kinase 1. These data demonstrate that apoptosis can be inhibited by an endogenous cellular protein by a mechanism that requires the activation of a single member of the mitogen-activating protein kinase family.