Immune Reconstitution during Pneumocystis Lung Infection: Disruption of Surfactant Component Expression and Function by S-Nitrosylation

Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
The Journal of Immunology (Impact Factor: 4.92). 02/2009; 182(4):2277-87. DOI: 10.4049/jimmunol.0802775
Source: PubMed


Pneumocystis pneumonia (PCP), the most common opportunistic pulmonary infection associated with HIV infection, is marked by impaired gas exchange and significant hypoxemia. Immune reconstitution disease (IRD) represents a syndrome of paradoxical respiratory failure in patients with active or recently treated PCP subjected to immune reconstitution. To model IRD, C57BL/6 mice were selectively depleted of CD4(+) T cells using mAb GK1.5. Following inoculation with Pneumocystis murina cysts, infection was allowed to progress for 2 wk, GK1.5 was withdrawn, and mice were followed for another 2 or 4 wk. Flow cytometry of spleen cells demonstrated recovery of CD4(+) cells to >65% of nondepleted controls. Lung tissue and bronchoalveolar lavage fluid harvested from IRD mice were analyzed in tandem with samples from CD4-depleted mice that manifested progressive PCP for 6 wks. Despite significantly decreased pathogen burdens, IRD mice had persistent parenchymal lung inflammation, increased bronchoalveolar lavage fluid cellularity, markedly impaired surfactant biophysical function, and decreased amounts of surfactant phospholipid and surfactant protein (SP)-B. Paradoxically, IRD mice also had substantial increases in the lung collectin SP-D, including significant amounts of an S-nitrosylated form. By native PAGE, formation of S-nitrosylated SP-D in vivo resulted in disruption of SP-D multimers. Bronchoalveolar lavage fluid from IRD mice selectively enhanced macrophage chemotaxis in vitro, an effect that was blocked by ascorbate treatment. We conclude that while PCP impairs pulmonary function and produces abnormalities in surfactant components and biophysics, these responses are exacerbated by IRD. This worsening of pulmonary inflammation, in response to persistent Pneumocystis Ags, is mediated by recruitment of effector cells modulated by S-nitrosylated SP-D.

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    • "In an infection based murine model of lung inflammation we have demonstrated that CD4 + T cell immune-reconstituted (IRD) mice infected with Pneumocystis pneumonia (Pc) exhibit impaired pulmonary function with substantial increases in the BAL SP-D level [4]. Snitrosylation of SP-D and therefore alteration in SP-D higher order structure were markedly enhanced by immune-reconstitution during Pc infection. "
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    ABSTRACT: Surfactant protein D (SP-D) is a member of the family of proteins termed collagen-like lectins or "collectins" that play a role in non-antibody-mediated innate immune responses [1]. The primary function of SP-D is the modulation of host defense and inflammation [2]. This review will discuss recent findings on the physiological importance of SP-D S-nitrosylation in biological systems and potential mechanisms that govern SP-D mediated signaling. SP-D appears to have both pro- and anti-inflammatory signaling functions. SP-D multimerization is a critical feature of its function and plays an important role in efficient innate host defense. Under baseline conditions, SP-D forms a multimer in which the N-termini are hidden in the center and the C-termini are on the surface. This multimeric form of SP-D is limited in its ability to activate inflammation. However, NO can modify key cysteine residues in the hydrophobic tail domain of SP-D resulting in a dissociation of SP-D multimers into trimers, exposing the S-nitrosylated N-termini. The exposed S-nitrosylated tail domain binds to the calreticulin/CD91 receptor complex and initiates a pro-inflammatory response through phosphorylation of p38 and NF-κB activation [3,4]. In addition, the disassembled SP-D loses its ability to block TLR4, which also results in activation of NF-κB. Recent studies have highlighted the capability of NO to modify SP-D through S-nitrosylation, causing the activation of a pro-inflammatory role for SP-D [3]. This represents a novel mechanism both for the regulation of SP-D function and NO's role in innate immunity, but also demonstrates that the S-nitrosylation can control protein function by regulating quaternary structure. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.
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    ABSTRACT: Nitric oxide (NO) is important for combating bacterial infections in the lungs. Levels of NO in the lungs are regulated by L-arginine, arginases (ARG) and NO synthases (NOS). Expression levels of ARG and inducible NOS (iNOS) vary among different types of macrophages (M0, M1, M2). Several events including infection, inflammation and tissue repair/resolution polarize macrophages (M0) into either M1 or M2 types. In general, M1 and M2 macrophages express high levels of iNOS and ARG, respectively. Classically activated M1 macrophages that are related to killing intracellular pathogens release T H 1 type cytokines (e.g., IFN, TNF, IL-1, IL-12) whereas the alternatively activated M2 macrophages that are involved in humoral immune response release T H 2 type cytokines (e.g., IL-4, IL-10). Based on the activating cytokines, M2 macrophages are further subdivided into M2a, M2b or M2c. Macrophage activation and polarization are also regulated by other soluble proteins such as the innate immune pattern-recognition collectins (collagenous lectins), surfactant protein (SP)-A and SP-D. These soluble defense molecules are known to recognize microbes, and agglutinate and/or form immune complexes to enhance pathogen clearance by macrophages. In the absence of SP-D, mouse alveolar macrophages show exaggerated M1-like phenotype. Certain microbial pathogens also modulate lung environment or macrophages to evade the nitric oxide-mediated immune response. In summary, interplay among microbes, cytokines, ARG, NOS and collectins regulate alveolar macrophage types and NO production in the lungs. The balance among these molecules appears to help eliminate microbial pathogens form the lungs with minimal inflammation.
    The Open Nitric Oxide Journal 05/2010; 2(2). DOI:10.2174/1875042701002020069
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