The role of nitric oxide in lung innate immunity: modulation by surfactant protein-A

Surfactant protein A (SP-A) and alveolar macrophages are essential components of lung innate immunity. Alveolar macrophages phagocytose and kill pathogens by the production of reactive oxygen and nitrogen species. In particular, peroxynitrite, the reaction product of superoxide and nitric oxide, appears to have potent antimicrobial effects. SP-A stimulates alveolar macrophages to phagocytose and kill pathogens and is important in host defense. However, SP-A has diverse effects on both innate and adaptive immunity, and may stimulate or inhibit immune function. SP-A appears to mediate toxic or protective effects depending on the immune status of the lung. In contrast to mouse or rat cells, it has been difficult to demonstrate nitric oxide production by human macrophages. We have recently demonstrated that human macrophages produce nitric oxide and use it to kill Klebsiella pneumoniae. SP-A either stimulates or inhibits this process, depending on the activation state of the macrophage. Given its diverse effects on immune function, SP-A may prove to be an effective therapy for both infectious and inflammatory diseases of the lung.     

Killing of Klebsiella pneumoniae by human alveolar macrophages

We investigated putative mechanisms by which human surfactant protein A (SP-A) effects killing of Klebsiella pneumoniae by human alveolar macrophages (AMs) isolated from bronchoalveolar lavagates of patients with transplanted lungs. Coincubation of AMs with human SP-A (25 microg/ml) and Klebsiella resulted in a 68% decrease in total colony forming units by 120 min compared with AMs infected with Klebsiella in the absence of SP-A, and this SP-A-mediated effect was abolished by preincubation with N(G)-monomethyl-L-arginine. Incubation of transplant AMs with SP-A increased intracellular Ca(2+) concentration ([Ca(2+)](i)) by 70% and nitrite and nitrate (NO(x)) production by 45% (from 0.24 +/- 0.02 to 1.3 +/- 0.21 nmol small middle dot 10(6) AMs(-1).h(-1)). Preincubation with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester inhibited the increase in [Ca(2+)](i) and abrogated the SP-A-mediated Klebsiella phagocytosis and killing. In contrast, incubation of AMs from normal volunteers with SP-A decreased both [Ca(2+)](i) and NO(x) production and did not result in killing of Klebsiella. Significant killing of Klebsiella was also seen in a cell-free system by sustained production of peroxynitrite (>1 microM/min) at pH 5 but not at pH 7.4. These findings indicate that SP-A mediates pathogen killing by AMs from transplant lungs by stimulating phagocytosis and production of reactive oxygen-nitrogen intermediates.     

The role of nitric oxide in lung innate immunity: Modulation by surfactant protein-A

Surfactant protein A (SP-A) and alveolar macrophages are essential components of lung innate immunity. Alveolar macrophages phagocytose and kill pathogens by the production of reactive oxygen and nitrogen species. In particular, peroxynitrite, the reaction product of superoxide and nitric oxide, appears to have potent antimicrobial effects. SP-A stimulates alveolar macrophages to phagocytose and kill pathogens and is important in host defense. However, SP-A has diverse effects on both innate and adaptive immunity, and may stimulate or inhibit immune function. SP-A appears to mediate toxic or protective effects depending on the immune status of the lung. In contrast to mouse or rat cells, it has been difficult to demonstrate nitric oxide production by human macrophages. We have recently demonstrated that human macrophages produce nitric oxide and use it to kill Klebsiella pneumoniae. SP-A either stimulates or inhibits this process, depending on the activation state of the macrophage. Given its diverse effects on immune function, SP-A may prove to be an effective therapy for both infectious and inflammatory diseases of the lung.     

Respiratory syncytial virus induces insensitivity to beta-adrenergic agonists in mouse lung epithelium in vivo

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants and children worldwide. We wished to determine whether intratracheal administration of beta-agonists improved alveolar fluid clearance (AFC) across the distal respiratory epithelium of RSV-infected mice. Following intranasal infection with RSV strain A2, AFC was measured in anesthetized, ventilated BALB/c mice by instillation of 5% BSA into the dependent lung. We found that direct activation of protein kinase A by forskolin or 8-bromo-cAMP increased AFC at day 2 after infection with RSV. In contrast, short- and long-acting beta-agonists had no effect at either day 2 or day 4. Insensitivity to beta-agonists was not a result of elevated plasma catecholamines or lung epithelial cell beta-adrenergic receptor degradation. Instead, RSV-infected mice had significantly higher levels of phosphorylated PKCzeta in the membrane fractions of their lung epithelial cells. In addition, insensitivity to beta-agonists was mediated in a paracrine fashion by KC (the murine homolog of CXCL8) and reversed by inhibition of either PKCzeta or G protein-coupled receptor kinase 2 (GRK2). These results indicate that insufficient response to beta-agonists in RSV may be caused, at least in part, by impaired beta-adrenergic receptor signaling, as a consequence of GRK2-mediated uncoupling of beta-adrenergic receptors from adenylyl cyclase.     

Comparison of methods for detection of pinworms in mice and rats

Though pinworm infestation remains common in laboratory rodent colonies, there is little information regarding current practices for pinworm detection and their relative efficacy. The authors surveyed research institutions to find out the prevalence of pinworm infestations and the detection methods they used. They also tested mice and rats from colonies that were known to be infested with Syphacia sp. and compared the following detection methods: perianal tape test, fecal flotation, fecal concentration, cecal content examination, cecal flotation and histological examination. Though the different methods yielded comparable efficacy overall, the authors recommend using more than one type of test to increase detection potential.     

Lung surfactant and reactive oxygen-nitrogen species: antimicrobial activity and host-pathogen interactions

Surfactant protein (SP) A and SP-D are members of the collectin superfamily. They are widely distributed within the lung, are capable of antigen recognition, and can discern self versus nonself. SPs recognize bacteria, fungi, and viruses by binding mannose and N-acetylglucosamine residues on microbial cell walls. SP-A has been shown to stimulate the respiratory burst as well as nitric oxide synthase expression by alveolar macrophages. Although nitric oxide (NO.) is a well-recognized microbicidal product of macrophages, the mechanism(s) by which NO. contributes to host defense remains undefined. The purpose of this symposium was to present current research pertaining to the specific role of SPs and reactive oxygen-nitrogen species in innate immunity. The symposium focused on the mechanisms of NO*-mediated toxicity for bacterial, human, and animal models of SP-A- and NO.-mediated pathogen killing, microbial defense mechanisms against reactive oxygen-nitrogen species, specific examples and signaling pathways involved in the SP-A-mediated killing of pulmonary pathogens, the structure and binding of SP-A and SP-D to bacterial targets, and the immunoregulatory functions of SP-A.