Modulation of alveolar macrophage phagocytosis by leukotrienes is Fc receptor-mediated and protein kinase C-dependent.
ABSTRACT We have previously established an important role for leukotrienes (LTs) in augmenting rat alveolar macrophage (AM) phagocytosis of Klebsiella pneumoniae opsonized with complete immune serum (IS), which contains the two well-known opsonins, immunoglobulin (Ig) G and complement (C). In this report, the specific opsonin requirements for LT modulation of AM phagocytosis and the dependence of this response on protein kinase (PK) C activity were investigated. Phagocytosis of K. pneumoniae opsonized with IS, non-immune serum, or heat-inactivated immune serum and of inert targets (IgG-opsonized fluorescent microspheres or C-opsonized sheep red blood cells) was examined. Inhibition of endogenous LT synthesis or action attenuated, whereas the addition of exogenous LTs augmented, phagocytosis only of targets opsonized with IgG. LTs had no effect on phagocytosis of C-opsonized or unopsonized targets. LTs did not affect adherence of IgG-opsonized targets, implying instead an enhancement of internalization. Macrophage internalization of phagocytic targets has previously been shown to require PKC activity. Pretreatment of AMs with the PKC inhibitors staurosporine or calphostin C, or with phorbol 12-myristate 13-acetate to deplete PKC, completely inhibited the ability of LTB(4) and largely inhibited the ability of LTC(4) to augment phagocytosis of IgG-opsonized microspheres. These results demonstrate that LT enhancement is confined to Fc receptor (FcR)-mediated phagocytosis. Moreover, PKC activation represents an important mechanism by which LTs promote FcR-mediated phagocytosis.
Article: 5-Lipoxygenase deficiency impairs innate and adaptive immune responses during fungal infection.[show abstract] [hide abstract]
ABSTRACT: 5-Lipoxygenase-derived products have been implicated in both the inhibition and promotion of chronic infection. Here, we sought to investigate the roles of endogenous 5-lipoxygenase products and exogenous leukotrienes during Histoplasma capsulatum infection in vivo and in vitro. 5-LO deficiency led to increased lung CFU, decreased nitric oxide production and a deficient primary immune response during active fungal infection. Moreover, H. capsulatum-infected 5-LO(-/-) mice showed an intense influx of neutrophils and an impaired ability to generate and recruit effector T cells to the lung. The fungal susceptibility of 5-LO(-/-) mice correlated with a lower rate of macrophage ingestion of IgG-H. capsulatum relative to WT macrophages. Conversely, exogenous LTB4 and LTC4 restored macrophage phagocytosis in 5-LO deficient mice. Our results demonstrate that leukotrienes are required to control chronic fungal infection by amplifying both the innate and adaptive immune response during histoplasmosis.PLoS ONE 01/2012; 7(3):e31701. · 4.09 Impact Factor
Article: Cigarette smoke exposure impairs pulmonary bacterial clearance and alveolar macrophage complement-mediated phagocytosis of Streptococcus pneumoniae.[show abstract] [hide abstract]
ABSTRACT: Cigarette smoke exposure increases the risk of pulmonary and invasive infections caused by Streptococcus pneumoniae, the most commonly isolated organism from patients with community-acquired pneumonia. Despite this association, the mechanisms by which cigarette smoke exposure diminishes host defense against S. pneumoniae infections are poorly understood. In this study, we compared the responses of BALB/c mice following an intratracheal challenge with S. pneumoniae after 5 weeks of exposure to room air or cigarette smoke in a whole-body exposure chamber in vivo and the effects of cigarette smoke on alveolar macrophage phagocytosis of S. pneumoniae in vitro. Bacterial burdens in cigarette smoke-exposed mice were increased at 24 and 48 h postinfection, and this was accompanied by a more pronounced clinical appearance of illness, hypothermia, and increased lung homogenate cytokines interleukin-1beta (IL-1beta), IL-6, IL-10, and tumor necrosis factor alpha (TNF-alpha). We also found greater numbers of neutrophils in bronchoalveolar lavage fluid recovered from cigarette smoke-exposed mice following a challenge with heat-killed S. pneumoniae. Interestingly, overnight culture of alveolar macrophages with 1% cigarette smoke extract, a level that did not affect alveolar macrophage viability, reduced complement-mediated phagocytosis of S. pneumoniae, while the ingestion of unopsonized bacteria or IgG-coated microspheres was not affected. This murine model provides robust additional support to the hypothesis that cigarette smoke exposure increases the risk of pneumococcal pneumonia and defines a novel cellular mechanism to help explain this immunosuppressive effect.Infection and immunity 12/2009; 78(3):1214-20. · 4.21 Impact Factor
Article: Disruption of leptin receptor-STAT3 signaling enhances leukotriene production and pulmonary host defense against pneumococcal pneumonia.[show abstract] [hide abstract]
ABSTRACT: The adipocyte-derived hormone leptin regulates energy homeostasis and the innate immune response. We previously reported that leptin plays a protective role in bacterial pneumonia, but the mechanisms by which leptin regulates host defense remain poorly understood. Leptin binding to its receptor, LepRb, activates multiple intracellular signaling pathways, including ERK1/2, STAT5, and STAT3. In this study, we compared the responses of wild-type and s/s mice, which possess a mutant LepRb that prevents leptin-induced STAT3 activation, to determine the role of this signaling pathway in pneumococcal pneumonia. Compared with wild-type animals, s/s mice exhibited greater survival and enhanced pulmonary bacterial clearance after an intratracheal challenge with Streptococcus pneumoniae. We also observed enhanced phagocytosis and killing of S. pneumoniae in vitro in alveolar macrophages (AMs) obtained from s/s mice. Notably, the improved host defense and AM antibacterial effector functions in s/s mice were associated with increased cysteinyl-leukotriene production in vivo and in AMs in vitro. Augmentation of phagocytosis in AMs from s/s mice could be blocked using a pharmacologic cysteinyl-leukotriene receptor antagonist. Phosphorylation of ERK1/2 and cytosolic phospholipase A(2) α, known to enhance the release of arachidonic acid for subsequent conversion to leukotrienes, was also increased in AMs from s/s mice stimulated with S. pneumoniae in vitro. These data indicate that ablation of LepRb-mediated STAT3 signaling and the associated augmentation of ERK1/2, cytosolic phospholipase A(2) α, and cysteinyl-leukotriene synthesis confers resistance to s/s mice during pneumococcal pneumonia. These data provide novel insights into the intracellular signaling events by which leptin contributes to host defense against bacterial pneumonia.The Journal of Immunology 01/2011; 186(2):1081-90. · 5.79 Impact Factor