Supernatants of virus-infected macrophages prime uninfected macrophages for lipopolysaccharide-induced apoptosis by both an interferon-dependent and an independent mechanism

The use of patient-derived breast tissue explants to study macrophage polarization and the effects of environmental chemical exposure

Ex vivo mammary explant systems are an excellent model to study interactions between epithelium and stromal cell types because they contain physiologically relevant heterotypic interactions in the background of genetically diverse patients. The intact human mammary tissue, termed patient-derived explant (PDE), can be used to investigate cellular responses to a wide variety of external stimuli in situ. For this study, we examined the impact of cytokines or environmental chemicals on macrophage phenotypes. We demonstrate that we can polarize macrophages within human breast tissue PDEs toward M1 or M2 through the addition of interferon-γ (IFNγ) + lipopolysaccharide (LPS) or interleukin (IL)-4 + IL-13, respectively. Elevated expression levels of M(IFNγ + LPS) markers (HLADRA and CXCL10) or M(IL-4 + IL-13) markers (CD209 and CCL18) were observed in cytokine-treated tissues. We also examined the impact of the endocrine-disrupting chemical, benzophenone-3, on PDEs and measured significant, yet varying effects on macrophage polarization. Furthermore, a subset of the PDEs respond to IL-4 + IL-13 through downregulation of E-cadherin and upregulation of vimentin which is reminiscent of epithelial-to-mesenchymal transition (EMT) changes. Finally, we were able to show immortalized nonmalignant breast epithelial cells can exhibit EMT characteristics when exposed to growth factors secreted by M(IL-4 + IL-13) macrophages. Taken together, the PDE model system is an outstanding preclinical model to study early tissue-resident immune responses and effects on epithelial and stromal responses to stimuli found both endogenously in the breast and exogenously as a result of exposures.

Apoptosis in Bovine viral diarrhea virus (BVDV)-induced mucosal disease lesions: a histological, immunohistological, and virological investigation

Cattle persistently infected with a noncytopathic Bovine viral diarrhea virus (BVDV) are at risk of developing fatal "mucosal disease" (MD). The authors investigated the role of various apoptosis pathways in the pathogenesis of lesions in animals suffering from MD. Therefore, they compared the expression of caspase-3, caspase-8, caspase-9, and Bcl-2L1 (Bcl-x) in tissues of 6 BVDV-free control animals, 7 persistently infected (PI) animals that showed no signs of MD (non-MD PI animals), and 11 animals with MD and correlated the staining with the localization of mucosal lesions. Caspase-3 and -9 staining were markedly stronger in MD cases and were associated with mucosal lesions, even though non-MD PI animals and negative controls also expressed caspase-9. Conversely, caspase-8 was not elevated in any of the animals analyzed. Interestingly, Bcl-x also colocalized with mucosal lesions in the MD cases. However, Bcl-x was similarly expressed in tissues from all 3 groups, and thus, its role in apoptosis needs to be clarified. This study clearly illustrates ex vivo that the activation of the intrinsic, but not the extrinsic, apoptosis pathway is a key element in the pathogenesis of MD lesions observed in cattle persistently infected with BVDV. However, whether direct induction of apoptosis in infected cells or indirect effects induced by the virus are responsible for the lesions observed remains to be established.

Simian varicella virus induces apoptosis in monkey kidney cells by the intrinsic pathway and involves downregulation of bcl-2 expression

Simian varicella virus (SVV) causes varicella in primates, becomes latent in ganglionic neurons, and reactivates to produce zoster. SVV produces a cytopathic effect in monkey kidney cells in tissue culture. To study the mechanism by which SVV-infected cells die, we examined markers of apoptosis 24 to 64 h postinfection (hpi). Western blot analysis of virus-infected cell lysates revealed a significant increase in the levels of the cleaved active form of caspase-3, accompanied by a parallel increase in caspase-3 activity at 40 to 64 hpi. Caspase-9, a marker for the intrinsic pathway, was activated significantly in SVV-infected cells at all time points, whereas trace levels of the active form of caspase-8, an extrinsic pathway marker, was detected only at 64 hpi. Bcl-2 expression at the mRNA and protein levels was decreased by 50 to 70% throughout the course of virus infection. Release of cytochrome c, an activator of caspase-9, from mitochondria into the cytoplasm was increased by 200% at 64 hpi. Analysis of Vero cells infected with SVV expressing green fluorescent protein (SVV-GFP) at 64 hpi revealed colocalization of the active forms of caspase-3 and caspase-9 and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) staining with GFP. A significant decrease in the bcl-2 mRNA levels along with an abundance of mRNA specific for SVV genes 63, 40, and 21 was seen in the fraction of Vero cells that were infected with SVV-GFP. Together, these findings indicate that SVV induces apoptosis in cultured Vero cells through the intrinsic pathway in which Bcl-2 is downregulated.

MEF2C mediates the activation induced cell death (AICD) of macrophages

Activation-induced cell death (AICD) of immune cells is widely believed to be crucial for the regulation of immune responses. Although macrophage apoptosis has been observed under a variety of pathological conditions, questions as to whether there is AICD of macrophages and how macrophage life span is regulated have not been well addressed. AICD in macrophages requires two signals. One is cell activation triggered by LPS or other bacterial components. The other is an event that exists in AICD-susceptible (primed) but not unsusceptible (resting) macrophages. Here we show that RAW264.7 cell is susceptible to LPS stimulation when it is primed with Salmonella typhimurium, type 5 adenovirus (Ad5) or IFN-gamma. We found that the stability of the transcription factor MEF2C is increased in primed RAW264.7 cell. Transfection of a dominant negative form of MEF2C protects primed macrophage from cell death triggered by LPS. Our data demonstrate that the increase of MEF2C protein stability is a key factor in the AICD of macrophage.

Induction of apoptosis in bone marrow neutrophil-lineage cells by classical swine fever virus

The pathogenesis of bone marrow atrophy during classical swine fever (CSF) was investigated in vitro by using CSF virus (CSFV) infection of bone marrow haematopoietic cells (BMHC). The monocytic lineage had the highest susceptibility to CSFV infection, whereas the more mature SWC8+ granulocytic cells were not directly susceptible to infection. However, myelomonocytic precursors were targets for CSFV infection and continued to differentiate into SWC8+ granulocytic cells, which remained infected. This explains the occurrence of infected peripheral blood granulocytes during CSF. The infection of BMHC resulted in increased apoptosis and necrosis, mainly within the granulocytic lineage. Caspases 3 and 9 were particularly activated, relating to the mitochondrial pathway of apoptosis. Interestingly, the majority of infected cells were non-apoptotic, the apoptotic cells being primarily non-infected. This indicated an indirect mechanism for induction of apoptosis, but no role could be identified for bone marrow stroma cells such as macrophages or fibroblastoid cells. Furthermore, soluble factors including cytokines and reactive oxygen species were not primarily responsible. In contrast, contact between infected and non-infected BMHC was critical for increasing apoptosis in the latter. Taken together, these results in vitro relate to and help to explain further the apoptosis of BMHC that occurs in vivo during CSF. This experimental system will also be particularly useful for the study of CSFV gene products involved in leukocyte apoptosis.