Pneumocystis carinii pneumonia alters expression and distribution of lung collectins SP-A and SP-D

Activation of alveolar epithelial ER stress by β-coronavirus infection disrupts surfactant homeostasis in mice: implications for COVID-19 respiratory failure

COVID-19 syndrome is characterized by acute lung injury, hypoxemic respiratory failure, and high mortality. Alveolar type 2 (AT2) cells are essential for gas exchange, repair, and regeneration of distal lung epithelium. We have shown that the causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and other members of the β-coronavirus genus induce an endoplasmic reticulum (ER) stress response in vitro; however, the consequences for host AT2 cell function in vivo are less understood. To study this, two murine models of coronavirus infection were used-mouse hepatitis virus-1 (MHV-1) in A/J mice and a mouse-adapted SARS-CoV-2 strain. MHV-1-infected mice exhibited dose-dependent weight loss with histological evidence of distal lung injury accompanied by elevated bronchoalveolar lavage fluid (BALF) cell counts and total protein. AT2 cells showed evidence of both viral infection and increased BIP/GRP78 expression, consistent with activation of the unfolded protein response (UPR). The AT2 UPR included increased inositol-requiring enzyme 1α (IRE1α) signaling and a biphasic response in PKR-like ER kinase (PERK) signaling accompanied by marked reductions in AT2 and BALF surfactant protein (SP-B and SP-C) content, increases in surfactant surface tension, and emergence of a reprogrammed epithelial cell population (Krt8+ and Cldn4+). The loss of a homeostatic AT2 cell state was attenuated by treatment with the IRE1α inhibitor OPK-711. As a proof-of-concept, C57BL6 mice infected with mouse-adapted SARS-CoV-2 demonstrated similar lung injury and evidence of disrupted surfactant homeostasis. We conclude that lung injury from β-coronavirus infection results from an aberrant host response, activating multiple AT2 UPR stress pathways, altering surfactant metabolism/function, and changing AT2 cell state, offering a mechanistic link between SARS-CoV-2 infection, AT2 cell biology, and acute respiratory failure.NEW & NOTEWORTHY COVID-19 syndrome is characterized by hypoxemic respiratory failure and high mortality. In this report, we use two murine models to show that β-coronavirus infection produces acute lung injury, which results from an aberrant host response, activating multiple epithelial endoplasmic reticular stress pathways, disrupting pulmonary surfactant metabolism and function, and forcing emergence of an aberrant epithelial transition state. Our results offer a mechanistic link between SARS-CoV-2 infection, AT2 cell biology, and respiratory failure.

Detection of Cytokines and Collectins in Bronchoalveolar Fluid Samples of Patients Infected with Histoplasma capsulatum and Pneumocystis jirovecii

Histoplasmosis and pneumocystosis co-infections have been reported mainly in immunocompromised humans and in wild animals. The immunological response to each fungal infection has been described primarily using animal models; however, the host response to concomitant infection is unknown. The present work aimed to evaluate the pulmonary immunological response of patients with pneumonia caused either by Histoplasma capsulatum, Pneumocystis jirovecii, or their co-infection. We analyzed the pulmonary collectin and cytokine patterns of 131 bronchoalveolar lavage samples, which included HIV and non-HIV patients infected with H. capsulatum, P. jirovecii, or both fungi, as well as healthy volunteers and HIV patients without the studied fungal infections. Our results showed an increased production of the surfactant protein-A (SP-A) in non-HIV patients with H. capsulatum infection, contrasting with HIV patients (p < 0.05). Significant differences in median values of SP-A, IL-1β, TNF-α, IFN-γ, IL-18, IL-17A, IL-33, IL-13, and CXCL8 were found among all the groups studied, suggesting that these cytokines play a role in the local inflammatory processes of histoplasmosis and pneumocystosis. Interestingly, non-HIV patients with co-infection and pneumocystosis alone showed lower levels of SP-A, IL-1β, TNF-α, IFN-γ, IL-18, IL-17A, and IL-23 than histoplasmosis patients, suggesting an immunomodulatory ability of P. jirovecii over H. capsulatum response.

Surfactant Protein D Recognizes Multiple Fungal Ligands: A Key Step to Initiate and Intensify the Anti-fungal Host Defense

With limited therapeutic options and associated severe adverse effects, fungal infections are a serious threat to human health. Innate immune response mediated by pattern recognition proteins is integral to host defense against fungi. A soluble pattern recognition protein, Surfactant protein D (SP-D), plays an important role in immune surveillance to detect and eliminate human pathogens. SP-D exerts its immunomodulatory activity via direct interaction with several receptors on the epithelial cells lining the mucosal tracts, as well as on innate and adaptive immune cells. Being a C-type lectin, SP-D shows calcium- and sugar-dependent interactions with several glycosylated ligands present on fungal cell walls. The interactome includes cell wall polysaccharides such as 1,3-β-D-glucan, 1,6-β-D-glucan, Galactosaminogalactan Galactomannan, Glucuronoxylomannan, Mannoprotein 1, and glycosylated proteins such as gp45, gp55, major surface glycoprotein complex (gpA). Recently, binding of a recombinant fragment of human SP-D to melanin on the dormant conidia of Aspergillus fumigatus was demonstrated that was not inhibited by sugars, suggesting a likely protein-protein interaction. Interactions of the ligands on the fungal spores with the oligomeric forms of full-length SP-D resulted in formation of spore-aggregates, increased uptake by phagocytes and rapid clearance besides a direct fungicidal effect against C. albicans. Exogenous administration of SP-D showed significant therapeutic potential in murine models of allergic and invasive mycoses. Altered susceptibility of SP-D gene-deficient mice to various fungal infections emphasized relevance of SP-D as an important sentinel of anti-fungal immunity. Levels of SP-D in the serum or lung lavage were significantly altered in the murine models and patients of fungal infections and allergies. Here, we review the cell wall ligands of clinically relevant fungal pathogens and allergens that are recognized by SP-D and their impact on the host defense. Elucidation of the molecular interactions between innate immune humoral such as SP-D and fungal pathogens would facilitate the development of novel therapeutic interventions.

Collectins: Innate Immune Pattern Recognition Molecules

Collectins are collagen-containing C-type (calcium-dependent) lectins which are important pathogen pattern recognising innate immune molecules. Their primary structure is characterised by an N-terminal, triple-helical collagenous region made up of Gly-X-Y repeats, an a-helical coiled-coil trimerising neck region, and a C-terminal C-type lectin or carbohydrate recognition domain (CRD). Further oligomerisation of this primary structure can give rise to more complex and multimeric structures that can be seen under electron microscope. Collectins can be found in serum as well as in a range of tissues at the mucosal surfaces. Mannanbinding lectin can activate the complement system while other members of the collectin family are extremely versatile in recognising a diverse range of pathogens via their CRDs and bring about effector functions designed at the clearance of invading pathogens. These mechanisms include opsonisation, enhancement of phagocytosis, triggering superoxidative burst and nitric oxide production. Collectins can also potentiate the adaptive immune response via antigen presenting cells such as macrophages and dendritic cells through modulation of cytokines and chemokines, thus they can act as a link between innate and adaptive immunity. This chapter describes the structure-function relationships of collectins, their diverse functions, and their interaction with viruses, bacteria, fungi and parasites.

Altered Surfactant Protein Expression in Primary Acquired Nasolacrimal Duct Obstruction

PURPOSE

To investigate the presence and distribution patterns of 6 surfactant proteins in lacrimal drainage tissues of patients with primary acquired nasolacrimal duct (NLD) obstruction.

METHODS

The presence and distribution of surfactant proteins (SP)-G and SP-H was first assessed in normal cadaveric lacrimal systems. The study was then performed in 10 samples of lacrimal sac and the respective NLDs obtained from patients suffering from primary acquired NLD obstruction who underwent either a dacryocystorhinostomy or a dacryocystectomy. The lacrimal sac samples were further divided into fundus and body, soon after their removal. Immunohistochemical labeling was performed for assessing the presence and distribution of SPs: SP-A, SP-B, SP-C, SP-D, SP-G/SFTA2, and SP-H/SFTA3. The results were then scored as positive or negative and the distribution pattern, if any, within the lacrimal sac and NLDs was assessed. Human lung tissues were used as controls.

RESULTS

SP-H was demonstrated in the lining epithelia of the normal lacrimal drainage systems, whereas SP-G was uniformly negative. Immunohistochemical labeling revealed wide variations in the staining patterns of different SPs in different regions of the lacrimal sac and the NLD. SP-D and SP-G revealed uniformly negative immunoreactivity. Variable staining patterns were also noted between the superficial and basal layers of the lining epithelia. However, the goblet cells and intraepithelial mucous glands did not express any of the SPs.

CONCLUSIONS

This study provides a proof of principle for the presence of SP-H and absence of SP-G in the normal lacrimal drainage systems. In cases of primary acquired nasolacrimal duct obstruction, there were alterations or loss of SP expression in the lining epithelia of the lacrimal sac and NLDs, reflecting their possible role in the etiopathogenesis of primary acquired nasolacrimal duct obstruction.In cases of primary-acquired nasolacrimal duct obstruction, the expression of multiple surfactant proteins was either deranged or lost in the lining epithelium of the lacrimal sac and nasolacrimal ducts.

C-type Lectins in Immunity to Lung Pathogens

The respiratory tract is tasked with responding to a constant and vast influx of foreign agents. It acts as an important first line of defense in the innate immune system and as such plays a crucial role in preventing the entry of invading pathogens. While physical barriers like the mucociliary escalator exert their effects through the clearance of these pathogens, diverse and dynamic cellular mechanisms exist for the activation of the innate immune response through the recognition of pathogen-associated molecular patterns (PAMPs). These PAMPs are recognized by pattern recognition receptors (PRRs) that are expressed on a number of myeloid cells such as dendritic cells, macrophages, and neutrophils found in the respiratory tract. C-type lectin receptors (CLRs) are PRRs that play a pivotal role in the innate immune response and its regulation to a variety of respiratory pathogens such as viruses, bacteria, and fungi. This chapter will describe the function of both activating and inhibiting myeloid CLRs in the recognition of a number of important respiratory pathogens as well as the signaling events initiated by these receptors.

Expression of mutant Sftpc in murine alveolar epithelia drives spontaneous lung fibrosis

Epithelial cell dysfunction is postulated as an important component in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Mutations in the surfactant protein C (SP-C) gene (SFTPC), an alveolar type II (AT2) cell-restricted protein, have been found in sporadic and familial IPF. To causally link these events, we developed a knockin mouse model capable of regulated expression of an IPF-associated isoleucine-to-threonine substitution at codon 73 (I73T) in Sftpc (SP-CI73T). Tamoxifen-treated SP-CI73T cohorts developed rapid increases in SftpcI73T mRNA and misprocessed proSP-CI73T protein accompanied by increased early mortality (days 7-14). This acute phase was marked by diffuse parenchymal lung injury, tissue infiltration by monocytes, polycellular alveolitis, and elevations in bronchoalveolar lavage and AT2 mRNA content of select inflammatory cytokines. Resolution of alveolitis (2-4 weeks), commensurate with a rise in TGF-β1, was followed by aberrant remodeling marked by collagen deposition, AT2 cell hyperplasia, α-smooth muscle actin-positive (α-SMA-positive) cells, and restrictive lung physiology. The translational relevance of the model was supported by detection of multiple IPF biomarkers previously reported in human cohorts. These data provide proof of principle that mutant SP-C expression in vivo causes spontaneous lung fibrosis, strengthening the role of AT2 cell dysfunction as a key upstream driver of IPF pathogenesis.

Surfactant proteins, SP-A and SP-D, in respiratory fungal infections: their role in the inflammatory response

Pulmonary surfactant is a complex fluid that comprises phospholipids and four proteins (SP-A, SP-B, SP-C, and SP-D) with different biological functions. SP-B, SP-C, and SP-D are essential for the lungs’ surface tension function and for the organization, stability and metabolism of lung parenchyma. SP-A and SP-D, which are also known as pulmonary collectins, have an important function in the host’s lung immune response; they act as opsonins for different pathogens via a C-terminal carbohydrate recognition domain and enhance the attachment to phagocytic cells or show their own microbicidal activity by increasing the cellular membrane permeability. Interactions between the pulmonary collectins and bacteria or viruses have been extensively studied, but this is not the same for fungal pathogens. SP-A and SP-D bind glucan and mannose residues from fungal cell wall, but there is still a lack of information on their binding to other fungal carbohydrate residues. In addition, both their relation with immune cells for the clearance of these pathogens and the role of surfactant proteins’ regulation during respiratory fungal infections remain unknown. Here we highlight the relevant findings associated with SP-A and SP-D in those respiratory mycoses where the fungal infective propagules reach the lungs by the airways.

Surfactant dysfunction and lung inflammation in the female mouse model of lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is a rare lung disease caused by mutations of the tumor suppressor genes, tuberous sclerosis complex (TSC) 1 or TSC2. LAM affects women almost exclusively, and it is characterized by neoplastic growth of atypical smooth muscle-like TSC2-null LAM cells in the pulmonary interstitium, cystic destruction of lung parenchyma, and progressive decline in lung function. In this study, we hypothesized that TSC2-null lesions promote a proinflammatory environment, which contributes to lung parenchyma destruction. Using a TSC2-null female murine LAM model, we demonstrate that TSC2-null lesions promote alveolar macrophage accumulation, recruitment of immature multinucleated cells, an increased induction of proinflammatory genes, nitric oxide (NO) synthase 2, IL-6, chemokine (C-C motif) ligand 2 (CCL2)/monocyte chemotactic protein 1 (MCP1), chemokine (C-X-C motif) ligand 1 (CXCL1)/keratinocyte chemoattractant (KC), and up-regulation of IL-6, KC, MCP-1, and transforming growth factor-β1 levels in bronchoalveolar lavage fluid. Bronchoalveolar lavage fluid also contained an increased level of surfactant protein (SP)-D, but not SP-A, significant reduction of SP-B levels, and a resultant increase in alveolar surface tension. Consistent with the growth of TSC2-null lesions, NO levels were also increased and, in turn, modified SP-D through S-nitrosylation, forming S-nitrosylated SP-D, a known consequence of lung inflammation. Progressive growth of TSC2-null lesions was accompanied by elevated levels of matrix metalloproteinase-3 and -9. This report demonstrates a link between growth of TSC2-null lesions and inflammation-induced surfactant dysfunction that might contribute to lung destruction in LAM.

[Significance of surfactant proteins in the diagnosis of therapeutic diseases]

The lung provides not only respiration, but also the functioning of innate immunity mechanisms. The hydrophilic proteins SP-A and SP-D are responsible for the regulation of the latter. In the literature, there is evidence for elevated serum SP-A and SP-D levels in respiratory diseases accompanied by enhanced mucosal inflammation of the lung or its parenchymal injury and their association with age and cardiovascular diseases has been recently found. Studies of the efficiency of using SP-A and SP-D as specific markers for inflammatory lung diseases are presently worthwhile.

A TLR4-interacting SPA4 peptide inhibits LPS-induced lung inflammation

The interaction between surfactant protein-A (SP-A) and TLR4 is important for host defense. We have recently identified an SPA4 peptide region from the interface of SP-A-TLR4 complex. Here, we studied the involvement of the SPA4 peptide region in SP-A-TLR4 interaction using a two-hybrid system, and biological effects of SPA4 peptide in cell systems and a mouse model. HEK293 cells were transfected with plasmid DNAs encoding SP-A or a SP-A-mutant lacking SPA4 peptide region and TLR4. Luciferase activity was measured as the end-point of SP-A-TLR4 interaction. NF-κB activity was also assessed simultaneously. Next, the dendritic cells or mice were challenged with Escherichia coli-derived LPS and treated with SPA4 peptide. Endotoxic shock-like symptoms and inflammatory parameters (TNF-α, NF-κB, leukocyte influx) were assessed. Our results reveal that the SPA4 peptide region contributes to the SP-A-TLR4 interaction and inhibits the LPS-induced NF-κB activity and TNF-α. We also observed that the SPA4 peptide inhibits LPS-induced expression of TNF-α, nuclear localization of NF-κB-p65 and cell influx, and alleviates the endotoxic shock-like symptoms in a mouse model. Our results suggest that the anti-inflammatory activity of the SPA4 peptide through its binding to TLR4 can be of therapeutic benefit.

Lung surfactant protein D (SP-D) response and regulation during acute and chronic lung injury

BACKGROUND

Surfactant protein D (SP-D) is a collection that plays important roles in modulating host defense functions and maintaining phospholipid homeostasis in the lung. The aim of current study was to characterize comparatively the SP-D response in bronchoalveolar lavage (BAL) and serum in three murine models of lung injury, using a validated ELISA technology for estimation of SP-D levels.

METHODS

Mice were exposed to lipopolysaccharide, bleomycin, or Pneumocystis carinii (Pc) and sacrificed at different time points.

RESULTS

In lipopolysaccharide-challenged mice, the level of SP-D in BAL increased within 6 h, peaked at 51 h (4,518 ng/ml), and returned to base level at 99 h (612 ng/ml). Serum levels of SP-D increased immediately (8.6 ng/ml), peaked at 51 h (16 ng/ml), and returned to base levels at 99 h (3.8 ng/ml). In a subacute bleomycin inflammation model, SP-D levels were 4,625 and 367 ng/ml in BAL and serum, respectively, 8 days after exposure. In a chronic Pc inflammation model, the highest level of SP-D was observed 6 weeks after inoculation, with BAL and serum levels of 1,868 and 335 ng/ml, respectively.

CONCLUSIONS

We conclude that serum levels of SP-D increase during lung injury, with a sustained increment during chronic inflammation compared with acute inflammation. A quick upregulation of SP-D in serum in response to acute airway inflammation supports the notion that SP-D translocates from the airways into the vascular system, in favor of being synthesized systemically. The study also confirms the concept of using increased SP-D serum levels as a biomarker of especially chronic airway inflammation.

Differential alveolar epithelial injury and protein expression in pneumococcal pneumonia

The integrity of the alveolar epithelium is a key factor in the outcome of acute lung injury. Here, we investigate alveolar epithelial injury and the expression of epithelial-selective markers in Streptococcus pneumoniae-induced acute lung injury. S. pneumoniae was instilled into rat lungs and alveolar type I (RTI(40)/podoplanin, MMC6 antigen) and alveolar type II (MMC4 antigen, surfactant protein D, pro-surfactant protein C, RTII(70)) cell markers were quantified in lavage fluid and lung tissue at 24 and 72 hours. The alveolar epithelium was also examined using electron, confocal, and light microscopy. S. pneumoniae induced an acute inflammatory response as assessed by increased total protein, SP-D, and neutrophils in lavage fluid. Biochemical and morphological studies demonstrated morphologic injury to type II cells but not type I cells. In particular, the expression of RTI(40)/podoplanin was dramatically reduced, on the surface of type I cells, in the absence of morphologic injury. These data demonstrate that type II cell damage can occur in the absence of type I cell injury without affecting the ability of the lung to return to a normal morphology. These data also demonstrate that RTI(40)/podoplanin is not a type I cell phenotypic marker in experimental acute lung injury caused by S. pneumoniae. Given that RTI(40)/podoplanin is an endogenous ligand for the C-type lectin receptor and this receptor plays a role in platelet aggregation and neutrophil activation, we hypothesize that the reduction of RTI(40)/podoplanin on type I cells might be important for the regulation of platelet and/or neutrophil function in experimental acute lung injury.

Outcomes and duration of Pneumocystis jiroveci pneumonia therapy in infants with severe combined immunodeficiency

This retrospective review of patients with severe combined immunodeficiency and Pneumocystis jiroveci pneumonia (PCP) evaluated the relationship between duration of therapy to treat PCP and overall survival. We found that 80% of patients receiving only 21 days of antibiotics survived to 12 months beyond hematopoietic cell transplant, whereas only 25% of patients who required longer treatment for PCP survived to stem cell engraftment.

Current understanding of Pneumocystis immunology

Pneumocystis jirovecii is the opportunistic fungal organism that causes Pneumocystis pneumonia (PCP) in humans. Similar to other opportunistic pathogens, Pneumocystis causes disease in individuals who are immunocompromised, particularly those infected with HIV. PCP remains the most common opportunistic infection in patients with AIDS. Incidence has decreased greatly with the advent of HAART. However, an increase in the non-HIV immunocompromised population, noncompliance with current treatments, emergence of drug-resistant strains and rise in HIV(+) cases in developing countries makes Pneumocystis a pathogen of continued interest and a public health threat. A great deal of research interest has addressed therapeutic interventions to boost waning immunity in the host to prevent or treat PCP. This article focuses on research conducted during the previous 5 years regarding the host immune response to Pneumocystis, including innate, cell-mediated and humoral immunity, and associated immunotherapies tested against PCP.

Pulmonary surfactant: an immunological perspective

Pulmonary surfactant has two crucial roles in respiratory function; first, as a biophysical entity it reduces surface tension at the air water interface, facilitating gas exchange and alveolar stability during breathing, and, second, as an innate component of the lung's immune system it helps maintain sterility and balance immune reactions in the distal airways. Pulmonary surfactant consists of 90% lipids and 10% protein. There are four surfactant proteins named SP-A, SP-B, SP-C, and SP-D; their distinct interactions with surfactant phospholipids are necessary for the ultra-structural organization, stability, metabolism, and lowering of surface tension. In addition, SP-A and SP-D bind pathogens, inflict damage to microbial membranes, and regulate microbial phagocytosis and activation or deactivation of inflammatory responses by alveolar macrophages. SP-A and SP-D, also known as pulmonary collectins, mediate microbial phagocytosis via SP-A and SP-D receptors and the coordinated induction of other innate receptors. Several receptors (SP-R210, CD91/calreticulin, SIRPalpha, and toll-like receptors) mediate the immunological functions of SP-A and SP-D. However, accumulating evidence indicate that SP-B and SP-C and one or more lipid constituents of surfactant share similar immuno-regulatory properties as SP-A and SP-D. The present review discusses current knowledge on the interaction of surfactant with lung innate host defense.

Effects of decreased calmodulin protein on the survival mechanisms of alveolar macrophages during Pneumocystis pneumonia

Pneumocystis infection causes increased intracellular levels of reactive oxygen species (ROS) and the subsequent apoptosis of alveolar macrophages (Amø). Assessments of key prosurvival molecules in Amø and bronchoalveolar lavage fluids from infected rats and mice showed low levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and reduced activation of phosphoinositide-3 kinase (PI-3K). Ubiquitous calcium-sensing protein calmodulin protein and mRNA levels were also reduced in Amø during Pneumocystis pneumonia (Pcp). Calmodulin has been implicated in control of GM-CSF production and PI-3K activation in other immune cell types. Experiments to determine the control of GM-CSF and PI-3K by calmodulin in Amø showed that GM-CSF expression and PI-3K activation could not be induced when calmodulin was inhibited. Calmodulin inhibition also led to increased levels of ROS and apoptosis in cells exposed to bronchoalveolar lavage fluids from infected animals. Supplementation of Amø with exogenous calmodulin increased survival signaling via GM-CSF and PI-3K and reduced ROS and apoptosis. These data support the hypotheses that calmodulin levels at least partially control survival signaling in Amø and that restoration of GM-CSF or PI-3K signaling will improve host response to the organism.

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.

Post hoc analysis of calfactant use in immunocompromised children with acute lung injury: Impact and feasibility of further clinical trials

OBJECTIVE

To assess the impact of calfactant (a modified natural bovine lung surfactant) in immunocompromised children with acute lung injury and to determine the number of patients required for a definitive clinical trial of calfactant in this population.

DESIGN

Post hoc analysis of data from a previous randomized, control trial.

SETTING

Tertiary care pediatric intensive care units.

PATIENTS

All children, defined as immunocompromised, enrolled in a multicenter, masked, randomized, control trial of calfactant for acute lung injury conducted between July 2000 and July 2003.

INTERVENTIONS

Patients received either an intratracheal instillation of calfactant or an equal volume of air placebo in a protocolized manner.

MEASUREMENTS AND MAIN RESULTS

Eleven of 22 (50%) calfactant-treated patients died when compared with 18 of 30 (60%) placebo patients (absolute risk reduction 10.0%, 95% confidence interval [CI] -17.3, 37.3). Among the 23 patients with an initial oxygen index (OI) >/=13 and </=37, 44% (4 of 9) of calfactant-treated patients died in comparison with 71% (10 of 14) of placebo (absolute risk reduction 27.0%, 95% CI -13.2, 67.2). Only 33% (3 of 9) of calfactant patients died before intensive care discharge in comparison with 71% (10 of 14) of placebo (absolute risk reduction 38.1%, 95% CI -0.7, 76.9). Calfactant therapy was associated with improved oxygenation in these 23 patients. Using an OI entry criterion of (13 </= OI </= 37), stratifying on the presence of hematopoietic stem cell transplantation, and accepting the 27% difference in mortality observed in this analysis, 63 patients would be required in each arm of a randomized, control trial to demonstrate a significant effect of calfactant on mortality in this patient population assuming a two-sided alpha of 0.05 and a power of 0.85.

CONCLUSIONS

These preliminary data suggest a potential benefit of calfactant in this high-risk population. A clinical trial powered to appropriately assess these findings seems warranted and feasible.

Regulation of surfactant protein D in the rodent prostate

BACKGROUND

Surfactant protein D (SP-D) is an innate immune protein that is present in mucosal lined surfaces throughout the human body, including the male reproductive tract. In the present study, we characterized the regulation of SP-D expression in the mouse and rat prostate.

METHODS

Real time reverse transcriptase polymerase chain reaction (RT-PCR) and immunostaining were used to characterize SP-D mRNA and protein in the mouse male reproductive tract. In order to evaluate the effects of testosterone on SP-D gene expression, we measured SP-D mRNA levels via real time RT-PCR in prostates from sham-castrated mice and castrated mice. In addition, we used a rat prostatitis model in which Escherichia coli was injected into the prostate in vivo to determine if infection influences SP-D protein levels in the prostate.

RESULTS

We found that SP-D mRNA and protein are present throughout the mouse male reproductive tract, including in the prostate. We determined that castration increases prostate SP-D mRNA levels (~7 fold) when compared to levels in sham-castrated animals. Finally, we demonstrated that infection in the prostate results in a significant increase in SP-D content 24 and 48 hours post-infection.

CONCLUSION

Our results suggest that infection and androgens regulate SP-D in the prostate.

Polyamine-mediated apoptosis of alveolar macrophages during Pneumocystis pneumonia

The number of alveolar macrophages is decreased during Pneumocystis pneumonia (Pcp), partly because of activation of apoptosis in these cells. This apoptosis occurs in both rat and mouse models of Pcp. Bronchoalveolar lavage (BAL) fluids from Pneumocystis-infected animals were found to contain high levels of polyamines, including spermidine, N1-acetylspermine, and N1-acetylspermidine. These BAL fluids and exogenous polyamines were able to induce apoptosis in alveolar macrophages. Apoptosis of alveolar macrophages during infection, after incubation with BAL fluids from Pneumocystis-infected animals, or after incubation with polyamines was marked by an increase in intracellular reactive oxygen species, activation of caspases-3 and -9, DNA fragmentation, and leakage of mitochondrial cytochrome c into the cytoplasm. When polyamines were depleted from the BAL fluids of infected animals, the ability of these BAL fluids to induce apoptosis was lost. Interestingly, the apoptosis inducing activity of the polyamine-depleted BAL fluids was restored when polyamines were added back. The results of this study suggested that Pneumocystis infection results in accumulation of high levels of polyamines in the lung. These polyamines activate apoptosis of alveolar macrophages, perhaps because of the ROS that are produced during polyamine metabolism.

Pulmonary surfactant in patients with Pneumocystis pneumonia and acquired immunodeficiency syndrome

OBJECTIVE

Pneumocystis pneumonia (PCP) is a severe infection of the immunocompromised host, resulting in diffuse alveolar damage and life-threatening respiratory failure. We analyzed pulmonary surfactant composition and function in bronchoalveolar lavage fluid (BALF) from ventilated and spontaneously breathing HIV-positive patients with PCP.

DESIGN

Prospective clinical trial.

SETTING

University hospital intensive care unit.

PATIENTS

Thirty-four spontaneously breathing (SB-PCP) and 20 ventilated HIV-positive patients with PCP (V-PCP), ten patients with acute respiratory distress syndrome (ARDS), 11 spontaneously breathing patients with bacterial pneumonia (PNEU), and 22 healthy volunteers.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Total phospholipid in BALF did not differ between any category vs. controls, whereas total protein increased approximately 14-fold in V-PCP and five-fold in SB-PCP compared with controls (p < .001). The relative content of large surfactant aggregates (LA) was reduced in SB-PCP and V-PCP compared with controls (p < .05). The phospholipid and fatty acid profiles showed a significant reduction in the relative content of phosphatidylcholine (PC), phosphatidylglycerol, and palmitic acid in PC in all patient categories compared with controls, with more in V-PCP (p < .001) compared with SB-PCP (p < .05). The neutral lipid-to-phospholipid ratio in LA was three-fold elevated in V-PCP (p < .01 compared with control) but not in SB-PCP. Analysis of neutral lipid classes showed a significant increase in the relative content of triglycerides and a reduction in free fatty acids in V-PCP compared with controls. BALF surfactant protein (SP)-A and SP-D significantly increased in V-PCP and SB-PCP, but not in ARDS and PNEU, compared with controls (p < .05). SP-B and SP-C content in LA remained unchanged in PCP compared with controls but decreased significantly in ARDS and PNEU. The minimum surface tension of LA was impaired (p < .001) in V-PCP more than in SB-PCP and was strongly correlated with the reduction in palmitic acid levels in PC LA (r = -.81). Reductions in phosphatidylglycerol strongly correlated with decreased Pao2/Fio2 values (r = .72).

CONCLUSIONS

We conclude that severe alterations in surfactant function and composition occur in patients with PCP and are even more pronounced in ventilated patients than in nonventilated patients. Surfactant lipid changes in PCP, but not surfactant protein profiles, closely resemble those found in ARDS.

IL-4 and IL-13 form a negative feedback circuit with surfactant protein-D in the allergic airway response

The innate immune molecule surfactant protein-D (SP-D) plays an important regulatory role in the allergic airway response. In this study, we demonstrate that mice sensitized and challenged with either Aspergillus fumigatus (Af) or OVA have increased SP-D levels in their lung. SP-D mRNA and protein levels in the lung also increased in response to either rIL-4 or rIL-13 treatment. Type II alveolar epithelial cell expression of IL-4Rs in mice sensitized and challenged with Af, and in vitro induction of SP-D mRNA and protein by IL-4 and IL-13, but not IFN-gamma, suggested a direct role of IL-4R-mediated events. The regulatory function of IL-4 and IL-13 was further supported in STAT-6-deficient mice as well as in IL-4/IL-13 double knockout mice that failed to increase SP-D production upon allergen challenge. Interestingly, addition of rSP-D significantly inhibited Af-driven Th2 cell activation in vitro whereas mice lacking SP-D had increased numbers of CD4(+) cells with elevated IL-13 and thymus- and activation-regulated chemokine levels in the lung and showed exaggerated production of IgE and IgG1 following allergic sensitization. We propose that allergen exposure induces elevation in SP-D protein levels in an IL-4/IL-13-dependent manner, which in turn, prevents further activation of sensitized T cells. This negative feedback regulatory circuit could be essential in protecting the airways from inflammatory damage after allergen inhalation.

Alveolar surfactant protein D content modulates bleomycin-induced lung injury

RATIONALE

Surfactant protein D (SP-D) is a collectin family member with demonstrated immunomodulatory properties in vitro. We hypothesized that SP-D modulates inflammation during noninfectious lung injury in vivo.

OBJECTIVES

To investigate the association of alveolar SP-D and injury, we studied the responses of transgenic mice expressing varying levels of SP-D to intratracheal bleomycin (ITB).

METHODS

Eight-week old C57/BL6 SP-D-deficient (-/-) mice and syngeneic wild-type (WT) controls or Swiss Black SP-D-overexpressing (SP-D OE) mice and littermate controls received either ITB or saline and were followed for up to 21 d.

MEASUREMENTS AND RESULTS

Kaplan-Meier analysis demonstrated a dose-dependent decrease in survival in ITB SP-D (-/-) mice receiving 2 U/kg bleomycin, with a 14-d mortality of 100% versus 0% mortality for WT receiving 2 U/kg ITB or SP-D (-/-) mice given saline (p < 0.05). At 8 d, ITB SP-D (-/-) mice had greater respiratory distress (frequency/tidal volume) and weight loss than ITB WT mice. Furthermore, bronchoalveolar lavage cellularity, pulmonary parenchymal inflammation, and tissue 3-nitrotyrosine (NO2 Y) were increased to a greater extent in ITB SP-D (-/-) mice. By 21 d, compared with all groups, ITB SP-D (-/-) survivors had increased Trichrome staining and tissue hydroxyproline levels. As proof of principle, SP-D OE mice were highly resistant to bleomycin-induced morbidity and mortality at doses up to 3 U/kg.

CONCLUSIONS

These data provide new in vivo evidence for an antiinflammatory role for SP-D in response to noninfectious, subacute lung injury via modulation of oxidative-nitrative stress.

Surfactant protein D enhances Pneumocystis infection in immune-suppressed mice

To further determine the role of surfactant protein (SP)-D in the pathogenesis of Pneumocystis pneumonia, a mouse model of transgenic overexpression (OE) of SP-D was studied. These animals produce roughly 30- to 50-fold greater SP-D than their wild-type (WT) counterparts but show no other differences in lung morphology and function. Animals in both the SP-D OE and WT groups were depleted of CD4 lymphocytes with weekly injections of GK1.5 antibody, before Pneumocystis inoculation, and throughout the subsequent infection period. At various time points, mice were killed and analyzed for inflammatory parameters and organism burden. Proinflammatory cytokines in bronchoalveolar lavage fluid were elevated throughout the period of infection, with OE animals exhibiting significantly higher levels of TNF-alpha and macrophage inflammatory protein-2 compared with WT controls. The total number of cells in the lavage fluid was also increased significantly only in the OE group, whereas the cell differential composition demonstrated lymphocyte and eosinophil infiltration in both groups of animals. Significantly, the organism burden was markedly higher in the SP-D OE animals, whereas the WT mice demonstrated little alteration in organism number over the course of infection. These results further indicate that SP-D facilitates the development of Pneumocystis infection and related lung inflammation in an immunosuppressed mouse model.

Surfactant protein-A inhibits Aspergillus fumigatus-induced allergic T-cell responses

BACKGROUND

The pulmonary surfactant protein (SP)-A has potent immunomodulatory activities but its role and regulation during allergic airway inflammation is unknown.

METHODS

We studied changes in SP-A expression in the bronchoalveolar lavage (BAL) using a murine model of single Aspergillus fumigatus (Af) challenge of sensitized animals.

RESULTS

SP-A protein levels in the BAL fluid showed a rapid, transient decline that reached the lowest values (25% of controls) 12 h after intranasal Af provocation of sensitized mice. Decrease of SP-A was associated with influx of inflammatory cells and increase of IL-4 and IL-5 mRNA and protein levels. Since levels of SP-A showed a significant negative correlation with these BAL cytokines (but not with IFN-gamma), we hypothesized that SP-A exerts an inhibitory effect on Th2-type immune responses. To study this hypothesis, we used an in vitro Af-rechallenge model. Af-induced lymphocyte proliferation of cells isolated from sensitized mice was inhibited in a dose-dependent manner by addition of purified human SP-A (0.1-10 microg/ml). Flow cytometric studies on Af-stimulated lymphocytes indicated that the numbers of CD4+ (but not CD8+) T cells were significantly increased in the parental population and decreased in the third and fourth generation in the presence of SP-A. Further, addition of SP-A to the tissue culture inhibited Af-induced IL-4 and IL-5 production suggesting that SP-A directly suppressed allergen-stimulated CD4+ T cell function.

CONCLUSION

We speculate that a transient lack of this lung collectin following allergen exposure of the airways may significantly contribute to the development of a T-cell dependent allergic immune response.

Surfactant protein A limits Pneumocystis murina infection in immunosuppressed C3H/HeN mice and modulates host response during infection

The development of Pneumocystis murina pneumonia and host response were characterized over time and at different levels of infection in corticosteroid immunosuppressed surfactant protein A (SP-A) knockout and wild-type (WT) mice. Infection increased over time in both strains of mice; however, significantly more cyst forms were detected in the knockout mice at intermediate and late stages of infection. In mice with heavy infections, TNF-alpha and IFN-gamma protein concentrations were significantly higher in pulmonary lavage fluid from knockout mice. There was a significant positive correlation between TNF-alpha and IFN-gamma concentrations and the level of infection in knockout mice, but not in WT mice. No significant differences were detected in IL-1 levels between the two strains of mice at any of the time points or at any level of infection. At heavier infection levels, significantly more MIP-2 protein was detected in the lungs of knockout mice, but a significant positive correlation between MIP-2 concentrations and the infection level was detected in both groups of mice. At the intermediate stage of infection, a significantly higher percentage of neutrophils was detected in the lungs of knockout mice than in WT mice. There was no difference in SP-D levels between WT and KO mice with identical levels of infection. These data support a protective role for SP-A in host defense against Pneumocystis and suggest that the effects of SP-A on the host response vary based on the intensity of the infection.

Strategic Targets of Essential Host-Pathogen Interactions

This review summarizes the present concepts regarding the biological processes that mediate intrinsic and innate host defense against microbial invasion of the lung. Innate immunity is the first line of defense of the higher organisms towards invading pathogens. It accomplishes a wide variety of activities including recognition and effector functions. The innate responses use phagocytic cells (macrophages, monocytes, and neutrophils), cells that release inflammatory mediators (basophils, mast cells, and eosinophils), and natural killer cells. The molecular component of innate responses includes complement, acute-phase proteins, and cytokines. Recognition of pathogen-associated molecular patterns is mediated by the pathogen receptors of the innate immune system, among these molecules toll-like receptors have emerged as fundamental components in the innate immune responses to infection, and a link between innate and adaptive immunity. Additional protection comes from polypeptide mediators of the innate host defense, such as the defensins and other antibiotic peptides. In view of the considerable burden in terms of mortality and morbidity that severe infections still pose worldwide, a better understanding of the biological basis of host-pathogen interactions opens stimulating future treatment perspectives.

Enhanced lung injury and delayed clearance of Pneumocystis carinii in surfactant protein A-deficient mice: attenuation of cytokine responses and reactive oxygen-nitrogen species

Surfactant protein A (SP-A), a member of the collectin family, selectively binds to Pneumocystis carinii and mediates interactions between pathogen and host alveolar macrophages in vitro. To test the hypothesis that mice lacking SP-A have delayed clearance of Pneumocystis organisms and enhanced lung injury, wild-type C57BL/6 (WT) and SP-A-deficient mice (SP-A(-/-)) with or without selective CD4(+)-T-cell depletion were intratracheally inoculated with Pneumocystis organisms. Four weeks later, CD4-depleted SP-A-deficient mice had developed a more severe Pneumocystis infection than CD4-depleted WT (P. carinii pneumonia [PCP] scores of 3 versus 2, respectively). Whereas all non-CD4-depleted WT mice were free of PCP, intact SP-A(-/-) mice also had evidence of increased organism burden. Pneumocystis infection in SP-A-deficient mice was associated histologically with enhanced peribronchial and/or perivascular cellularity (score of 4 versus 2, SP-A(-/-) versus C57BL/6 mice, respectively) and a corresponding increase in bronchoalveolar lavage (BAL) cell counts. Increases in SP-D content, gamma interferon, interleukin-4, interleukin-5, and tumor necrosis factor alpha in BAL fluid occurred but were attenuated in PCP-infected SP-A(-/-) mice compared to WT mice. There were increases in total BAL NO levels in both infected groups, but nitrite levels were higher in SP-A(-/-) mice, indicating a reduction in production of higher oxides of nitrogen that was also reflected in lower levels of 3-nitrotyrosine staining in the SP-A(-/-) group. We conclude that despite increases in inflammatory cells, SP-A-deficient mice infected with P. carinii exhibit an enhanced susceptibility to the organism and attenuated production of proinflammatory cytokines and reactive oxygen-nitrogen species. These data support the concept that SP-A is a local effector molecule in the lung host defense against P. carinii in vivo.

Collectins

Collectins are a family of collagenous calcium-dependent defense lectins in animals. Their polypeptide chains consist of four regions: a cysteine-rich N-terminal domain, a collagen-like region, an alpha-helical coiled-coil neck domain and a C-terminal lectin or carbohydrate-recognition domain. These polypeptide chains form trimers that may assemble into larger oligomers. The best studied family members are the mannan-binding lectin, which is secreted into the blood by the liver, and the surfactant proteins A and D, which are secreted into the pulmonary alveolar and airway lining fluid. The collectins represent an important group of pattern recognition molecules, which bind to oligosaccharide structures and/or lipid moities on the surface of microorganisms. They bind preferentially to monosaccharide units of the mannose type, which present two vicinal hydroxyl groups in an equatorial position. High-affinity interactions between collectins and microorganisms depend, on the one hand, on the high density of the carbohydrate ligands on the microbial surface, and on the other, on the degree of oligomerization of the collectin. Apart from binding to microorganisms, the collectins can interact with receptors on host cells. Binding of collectins to microorganisms may facilitate microbial clearance through aggregation, complement activation, opsonization and activation of phagocytosis, and inhibition of microbial growth. In addition, the collectins can modulate inflammatory and allergic responses, affect apoptotic cell clearance and modulate the adaptive immune system.

Surfactant protein-D, a mediator of innate lung immunity, alters the products of nitric oxide metabolism

Surfactant protein (SP)-D, a 43-kD multifunctional collagen-like lectin, is synthesized and secreted by the airway epithelium. SP-D knockout (SP-D [-/-]) mice exhibit an increase in the number and size of airway macrophages, peribronchiolar inflammation, increases in metalloproteinase activity, and development of emphysema. Nitric oxide (NO) is involved in a variety of signaling processes, and because altered NO metabolism has been observed in inflammation, we hypothesized that alterations in its metabolism would underlie the proinflammatory state observed in SP-D deficiency. Examination of the bronchial alveolar lavage (BAL) from SP-D (-/-) mice reveals a significant increase in protein and phospholipid content and total cell count. NO production and inducible NO synthase expression were increased in the BAL; however, there was a decline in S-nitrosothiol (SNO) content in the BAL and a loss of SNO immunoreactivity within the tissue. This decline in SNO was accompanied by an increase in nitrotyrosine staining. We conclude that inflammation that occurs in SP-D deficiency results in an increase in NO production and a shift in the chemistry and targets of NO. We speculate that the proinflammatory response due to SP-D deficiency results, in part, from a disruption of NO-mediated signaling within the innate immune system.

Attenuated allergic airway hyperresponsiveness in C57BL/6 mice is associated with enhanced surfactant protein (SP)-D production following allergic sensitization

Background

C57BL/6 mice have attenuated allergic airway hyperresponsiveness (AHR) when compared with Balb/c mice but the underlying mechanisms remain unclear. SP-D, an innate immune molecule with potent immunosuppressive activities may have an important modulatory role in the allergic airway response and the consequent physiological changes. We hypothesized that an elevated SP-D production is associated with the impaired ability of C57BL/6 mice to develop allergic AHR.

Methods

SP-D mRNA and protein expression was investigated during development of allergic airway changes in a model of Aspergillus fumigatus (Af)-induced allergic inflammation. To study whether strain dependency of allergic AHR is associated with different levels of SP-D in the lung, Balb/c and C57BL/6 mice were compared.

Results

Sensitization and exposure to Af induced significant airway inflammation in both mouse strains in comparison with naïve controls. AHR to acetylcholine however was significantly attenuated in C57BL/6 mice in spite of increased eosinophilia and serum IgE when compared with Balb/c mice (p < 0.05). Af challenge of sensitized C57BL/6 mice induced a markedly increased SP-D protein expression in the SA surfactant fraction (1,894 ± 170% of naïve controls) that was 1.5 fold greater than the increase in Balb/c mice (1,234 ± 121% p < 0.01). These changes were selective since levels of the hydrophobic SP-B and SP-C and the hydrophilic SP-A were significantly decreased following sensitization and challenge with Af in both strains. Further, sensitized and exposed C57BL/6 mice had significantly lower IL-4 and IL-5 in the BAL fluid than that of Balb/c mice (p < 0.05).

Conclusions

These results suggest that enhanced SP-D production in the lung of C57BL/6 mice may contribute to an attenuated AHR in response to allergic airway sensitization. SP-D may act by inhibiting synthesis of Th2 cytokines.

Surfactant protein D-mediated aggregation of Pneumocystis carinii impairs phagocytosis by alveolar macrophages

Pneumocystis carinii remains an important and potentially fatal cause of opportunistic pneumonia. Animal studies reveal that substantial quantities of surfactant protein D (SP-D) accumulate in the airspaces during P. carinii pneumonia and are particularly abundant in aggregates of organisms. Due to the multimeric structure of SP-D, we hypothesized that SP-D mediates aggregation of the organism. From previous clinical studies it is known that aggregated organisms are conspicuous in sections of lung tissue and bronchoalveolar lavage (BAL) fluids of humans with active P. carinii pneumonia. Herein, we observe that SP-D levels increased at least fourfold in BAL fluids of patients with P. carinii pneumonia. Next, a spectrophotometric sedimentation assay was developed to assess the aggregation of P. carinii in vitro by SP-D. P. carinii organisms were first stripped with glutathione to remove bound SP-D and subsequently incubated in the presence of SP-D and 2 mM calcium. P. carinii incubated with natural SP-D (10 micro g/ml) containing dodecamers and higher-order forms exhibited aggregation and enhanced sedimentation compared to that of glutathione-stripped P. carinii. Aggregation was also enhanced by the concentrated supernatant of rat BAL fluid, and this effect was abolished by the selective removal of SP-D from the lavage fluid. P. carinii aggregation was reduced by maltose, mannose, and EDTA, consistent with the role of the SP-D C-type lectin domain (CRD) in the aggregation event. Comparisons of different molecular forms of SP-D showed that dodecamers-but not trimeric subunits-mediate optimal aggregation of P. carinii. Aggregation of P. carinii by SP-D was shown to be responsible for the impaired phagocytosis of the organisms by alveolar macrophages. Thus, SP-D-mediated aggregation of P. carinii may represent one means by which the organism avoids elimination by the host.

The late asthmatic response is linked with increased surface tension and reduced surfactant protein B in mice

Pulmonary surfactant dysfunction may significantly contribute to small airway obstruction during the asthmatic response, but neither its exact role nor its regulation is clear. Surfactant function and composition was studied in an Aspergillus fumigatus (Af)-induced late-phase allergic airway response in sensitized BALB/c mice. The peak of Af-induced airway hyperresponsiveness in sensitized and challenged mice 24 h after allergen provocation coincided with a significant fall in surface activity of the pulmonary surfactant. The underlying changes included time-dependent elaboration of eotaxin and IL-5 followed by eosinophil influx into the airways. The height of airway inflammation and hyperresponsiveness was preceded by release of IL-4 and marked reductions in surfactant protein (SP)-B, a hydrophobic surfactant protein responsible for maintaining low surface tension of the lining fluid of distal air spaces. Furthermore, intratracheal administration of IL-4 significantly inhibited SP-B, indicating a regulatory role of this cytokine in the surfactant biophysical changes. Thus surfactant dysfunction induced by an IL-4-driven SP-B deficiency after allergen provocation may be an important part of the late asthmatic airway response.