SP-A and SP-D: Dual Functioning Immune Molecules With Antiviral and Immunomodulatory Properties.

Surfactant proteins A (SP-A) and D (SP-D) are soluble innate immune molecules which maintain lung homeostasis through their dual roles as anti-infectious and immunomodulatory agents. SP-A and SP-D bind numerous viruses including influenza A virus, respiratory syncytial virus (RSV) and human immunodeficiency virus (HIV), enhancing their clearance from mucosal points of entry and modulating the inflammatory response. They also have diverse roles in mediating innate and adaptive cell functions and in clearing apoptotic cells, allergens and other noxious particles. Here, we review how the properties of these first line defense molecules modulate inflammatory responses, as well as host-mediated immunopathology in response to viral infections. Since SP-A and SP-D are known to offer protection from viral and other infections, if their levels are decreased in some disease states as they are in severe asthma and chronic obstructive pulmonary disease (COPD), this may confer an increased risk of viral infection and exacerbations of disease. Recombinant molecules of SP-A and SP-D could be useful in both blocking respiratory viral infection while also modulating the immune system to prevent excessive inflammatory responses seen in, for example, RSV or coronavirus disease 2019 (COVID-19). Recombinant SP-A and SP-D could have therapeutic potential in neutralizing both current and future strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus as well as modulating the inflammation-mediated pathology associated with COVID-19. A recombinant fragment of human (rfh)SP-D has recently been shown to neutralize SARS-CoV-2. Further work investigating the potential therapeutic role of SP-A and SP-D in COVID-19 and other infectious and inflammatory diseases is indicated.

[ANTIINFLAMMATORY AND REGENERATIVE EFFECT OF PEPTIDE THERAPY IN THE MODEL OF OBSTRUCTIVE LUNG PATHOLOGY].

The effect of the tetrapeptide bronchogen on the structural and functional state of the bronchial epithelium and inflammatory activity in the lungs was studied in the chronic obstructive pulmonary disease (COPD) model, created in rats by a 60-day intermittent exposure to nitrogen dioxide. The cell composition and cytokine-enzyme profile of bronchoalveolar lavage fluid (BALF), the content of secretory immunoglobulin A and surfactant protein B in BALF were determined. Following the course of peptide treatment the decreased activity of neutrophilic inflammation with the normalization of cellular composition and profile of pro-inflammatory cytokines and enzymes in the bronchoalveolar space was observed. The structure of bronchial epithelium, disturbed during formation of COPD model, was restored and accompanied by restoration of its functional activity as evidenced by an increase of secretory immunoglobulin A (local immunity marker) and surfactant protein B, responsible for reducing the alveolar surface tension.

[EFFECT OF MAST CELL DEGRANULATION BLOCKADE ON THE INFLAMMATION OUTCOME IN THE MODEL OF OBSTRUCTIVE LUNG PATHOLOGY].

Effect of mast cell degranulation blockade on the inflammatory response and character of the lung tissue structure-functional changes were evaluated in the chronic obstructive pulmonary disease model produced in rats by 60-day intermittent exposure to nitrogen dioxide. The membrane stabilizer sodium cromoglicate was used to blockade of mast cell degranulation. Lung tissue sections were stained with toluidine blue to identify mast cells. Bronchoalveolar lavage fluid (BALF) cytogram was determined. The levels of mast cell tryptase and chymase, proinflammatory cytokine TNF-α, surfactant protein B were measured in BALF. Suppression of mast cell degranulation prevented the release of proteases in the bronchoalveolar space and reduced activity of the inflammatory process. The influx of inflammatory cells and TNF-α concentration decreased. There was no interstitial inflammatory infiltration. Bronchoalveolar epithelium structure was recovered that is the basis of its functional usefulness. The results confirm the active involvement of mast cells in the development of the inflammatory process in obstructive pulmonary diseases and allow us to consider them as a possible therapeutic target.

Immune reconstitution during Pneumocystis lung infection: disruption of surfactant component expression and function by S-nitrosylation.

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.

Intravenous lipopolysaccharide-induced pulmonary maturation and structural changes in fetal sheep.

BACKGROUND: Antenatal pulmonary inflammation is associated with reduced risk for respiratory distress syndrome but with an increased risk for bronchopulmonary dysplasia (BPD) with impaired alveogenesis. OBJECTIVE: We hypothesized that fetal systemic inflammation induced by intravenous (IV) lipopolysaccharide (LPS) would affect lung development in utero. STUDY DESIGN: Twenty-one fetal sheep were instrumented (107 days gestational age). Control fetuses received saline (N = 12) and 9 in the study group received 100 ng of LPS IV 3 days after surgery. Animals were assessed for lung maturation and structure after 3 (N = 5) and 7 (N = 4) days. RESULTS: Interleukin-6 concentration increased in the bronchoalveolar lavage more than 40-fold 3 days after LPS IV. Processing of pro-surfactant protein (SP)-B to mature SP-B and increased SP-B concentrations were shown 7 days after LPS IV. Deposition of elastin fibers at sites of septation was disturbed within 3 days after LPS IV. CONCLUSION: Lung maturation and disturbed lung structure occurred after short-term exposure to fetal inflammation and suggests new targeted therapies for BPD.

Stepwise examination for differential diagnosis of primary lung cancer and breast cancer relapse presenting as a solitary pulmonary nodule in patients after mastectomy.

BACKGROUND AND OBJECTIVES: The distinction of primary lung from metastatic breast cancer is crucial in patients presenting with a solitary pulmonary nodule after mastectomy, because treatment strategies are completely different. Definitive diagnosis of these nodules, however, is often difficult. We assessed the feasibility of our diagnostic approach for these nodules and estimated the frequency of primary lung cancer occurrence in patients after mastectomy. METHODS: We evaluated solitary pulmonary nodules appearing in 48 patients after mastectomy. For histological examination, CT-guided needle aspiration biopsy (CT-NAB) or trans-bronchial lung biopsy (TBLB) was performed. Besides conventional morphopathological examination, differential diagnosis was performed by immunohistochemical examination and evaluation using a molecular marker (mammaglobin 1). RESULTS: Biopsy specimens were obtained using minimally invasive methods, namely CT-NAB and TBLB, in 91.7% of patients. From 48 patients, differential diagnosis was obtained by morphopathological methods alone in 32, and by immunohistochemical and molecular marker examination in the remaining 16. Final diagnosis was metastatic breast and primary lung cancer in 40 (83.3%) and 8 patients (16.7%), respectively. CONCLUSIONS: Our results show the clinical feasibility of our stepwise approach to the differential diagnosis of primary lung cancer and breast cancer relapse presenting as a solitary nodule in patients after mastectomy.

Surfactant protein B detection and gene expression in chronic rhinosinusitis.

INTRODUCTION: Surfactant protein (SP)-B is a hydrophobic protein secreted within pulmonary surfactant that facilitates the adsorption of surface-active lipids to the air-liquid interface of the alveoli and increases alveolar stability. SP-B may also have anti-inflammatory properties. It is implicated in decreasing the pulmonary inflammatory response to bacterial lipopolysaccharide. However, the expression and function of SP-B in the sinonasal cavities has not been elucidated. Our objective was to detect the presence of SP-B, measure alterations in several forms of chronic rhinosinusitis (CRS), and localize cellular protein expression. MATERIALS/METHODS: Sinus mucosal biopsies were performed in patients with allergic fungal rhinosinusitis (AFRS), nonatopic CRS with nasal polyposis (NP), and cystic fibrosis (CF) and in healthy controls. SP-B mRNA was measured in CRS and control patients using quantitative polymerase chain reaction. Immunoblot analysis and immunolocalization of SP-B were also performed. RESULTS: CF (n = 4) showed significantly increased levels of SP-B (169-fold) mRNA (P = .004) when compared with controls (n = 5). CRS with NP (n = 5) and AFRS (n = 7) also demonstrated elevated levels of SP- B (14-fold and 4-fold, respectively) when compared with the control group, although these were not statistically significant. Immunoblot analysis confirmed the presence of the translated product, and immunolocalization revealed expression in the epithelium and submucosal glandular elements. CONCLUSION: This is the first study to detect and characterize SP-B in human sinus mucosa. Furthermore, SP-B is significantly up-regulated in CF CRS.

Pulmonary surfactant proteins A and D: innate immune functions and biomarkers for lung diseases.

Pulmonary surfactant, a complex of lipids and proteins, functions to keep alveoli from collapsing at expiration. Surfactant proteins A (SP-A) and D (SP-D) belong to the collectin family and play pivotal roles in the innate immunity of the lung. Pulmonary collectins directly bind with broad specificities to a variety of microorganism and possess anti-microbial effects. These proteins also exhibit both inflammatory and anti-inflammatory functions, which occur through interactions with pattern recognition receptors including Toll-like receptor and CD14, signal inhibitory regulatory protein alpha and a receptor complex of calreticulin and CD91. The collectins enhance phagocytosis of microbes by macrophages through opsonic and/or non-opsonic activities. The proteins stimulate cell surface expression of phagocytic receptors including scavenger receptor A and mannose receptor. Since the expression of SP-A and SP-D is abundant and restricted within the lung, the proteins are now clinically used as biomarkers for lung diseases. The levels of SP-A and SP-D in bronchoalveolar lavage fluids, amniotic fluids, tracheal aspirates and pleural effusions reflect alterations in alveolar compartments and epithelium, and lung maturity. The determination of SP-A and SP-D in sera is a non-invasive and useful tool for understanding some pathological changes of the lung in the diseases, including pulmonary fibrosis, collagen vascular diseases complicated with interstitial lung disease, pulmonary alveolar proteinosis, acute respiratory distress syndrome and radiation pneumonitis.

Antimicrobial peptides and surfactant proteins in ruminant respiratory tract disease.

In ruminants, respiratory disease is multifactorial and a leading cause of morbidity and mortality. Pulmonary innate immunity is the first line of defense for the respiratory tract. Alteration of regulation, expression, and function of these factors may be important to disease development and resolution. Many antimicrobial peptides and surfactant proteins are constitutively expressed in the respiratory tract and expression levels are regulated. Beta-defensins are cationic peptides with broad antimicrobial activity against bacterial, viral and fungal pathogens. Beta-defensins are primarily expressed in mucosal epithelia (and in some species leukocytes); where they may also participate in chemotaxis, wound repair and adaptive immune responses. Surfactant proteins A and D are secreted pulmonary surfactant proteins that have antimicrobial and immune regulatory activity. Anionic peptide is a constitutively expressed, aspartate-rich peptide that has antimicrobial activity and is most prominent during reparative epithelial hyperplasia. Regulation of these immune defense components by stress, pathogens, and inflammatory cytokines may play a role in the susceptibility to, severity and resolution of respiratory infection. The expression patterns of these molecules can be specific for host-species, class of pathogen and stage of infection. Understanding the regulation of antimicrobial peptide/protein expression will further enhance the potential for novel prophylactic and therapeutic modalities to minimize the impact of respiratory disease.

Surfactant protein B in type II pneumocytes and intra-alveolar surfactant forms of human lungs.

Surfactant protein B (SP-B) is synthesized by type II pneumocytes as a proprotein (proSP-B) that is proteolytically processed to an 8-kD protein. In human type II pneumocytes, we identified not only proSP-B, processing intermediates of proSP-B, and mature SP-B, but also fragments of the N-terminal propeptide. By means of immunoelectron microscopy, proSP-B and processing intermediates were localized in the endoplasmic reticulum, Golgi vesicles, and few multivesicular bodies in type II pneumocytes in human lungs. A colocalization of fragments of the N-terminal propeptide and mature SP-B was found in multivesicular, composite, and some lamellar bodies. Mature SP-B was localized over the projection core of lamellar bodies and core-like structures in tubular myelin figures. In line with immunoelectron microscopy and Western blot analysis of human type II pneumocytes, a fragment of the N-terminal propeptide was also detected in isolated rat lamellar bodies. In conclusion, our data indicate that the processing of proSP-B occurs between the Golgi complex and multivesicular bodies and provide evidence that a fragment of the N-terminal propeptide and mature SP-B are transported together to the lamellar bodies. In human lungs, mature SP-B is involved in the structural organization of lamellar bodies and tubular myelin by the formation of core particles.

Intersubunit disulfide bridge is not required for the protective role of SP-B against lung inflammation.

Surfactant protein B (SP-B) is known to promote surfactant phospholipid film formation and reduce surface tension. Native SP-B is a homodimer in which subunit association is stabilized via covalent linkage through cysteine 48. We hypothesized that loss of the intersubunit bridge would alter SP-B function and lead to increased inflammation in response to challenge by hyperoxia or endotoxin. Transgenic mice in which SP-B cysteine 48 was mutated to serine were generated and crossed into the SP-B(-/-) background. Wild-type mice and transgenic mice carrying a single copy (SP-Bmon(+)) or two copies (SP-Bmon(++)) of the transgene were exposed to 95% O2 for 3 days or intratracheally injected with 10 microg of endotoxin. Interleukin-1beta, major intrinsic protein 2, and interleukin-6 in lung homogenates after 3 days of hyperoxia were significantly higher (P < 0.001) in SP-Bmon(+) mice than SP-Bmon(++) or wild-type mice. At 16 h after endotoxin injection, cytokines in lung tissues were higher in SP-Bmon(+) mice compared with wild-type mice (P < 0.05). Consistent with prolonged recovery in SP-Bmon(+) mice, the percentage of apoptotic cells in alveolar lavage was significantly lower in SP-Bmon(+) mice than in SP-Bmon(++) and wild-type mice. Overall, increased inflammation in SP-Bmon(+) mice was corrected to a large extent by increased gene dosage, indicating that formation of the intersubunit disulfide bridge is not critical for SP-B function.