Structures and functions of mammalian collectins

Avian surfactant protein (SP)-A2 first arose in an early tetrapod before the divergence of amphibians and gradually lost the collagen domain

The air-liquid interface of the mammalian lung is lined with pulmonary surfactants, a mixture of specific proteins and lipids that serve a dual purpose-enabling air-breathing and protection against pathogens. In mammals, surfactant proteins A (SP-A) and D (SP -D) are involved in innate defence of the lung. Birds seem to lack the SP-D gene, but possess SP-A2, an additional SP-A-like gene. Here we investigated the evolution of the SP-A and SP-D genes using computational gene prediction, homology, simulation modelling and phylogeny with published avian and other vertebrate genomes. PCR was used to confirm the identity and expression of SP-A analogues in various tissue homogenates of zebra finch and turkey. In silico analysis confirmed the absence of SP-D-like genes in all 47 published avian genomes. Zebra finch and turkey SP-A1 and SP-A2 sequences, confirmed by PCR of lung homogenates, were compared with sequenced and in silico predicted vertebrate homologs to construct a phylogenetic tree. The collagen domain of avian SP-A1, especially that of zebra finch, was dramatically shorter than that of mammalian SP-A. Amphibian and reptilian genomes also contain avian-like SP-A2 protein sequences with a collagen domain. NCBI Gnomon-predicted avian and alligator SP-A2 proteins all lacked the collagen domain completely. Both avian SP-A1 and SP-A2 sequences form separate clades, which are most closely related to their closest relatives, the alligators. The C-terminal carbohydrate recognition domain (CRD) of zebra finch SP-A1 was structurally almost identical to that of rat SP-A. In fact, the CRD of SP-A is highly conserved among all the vertebrates. Birds retained a truncated version of mammalian type SP-A1 as well as a non-collagenous C-type lectin, designated SP-A2, while losing the large collagenous SP-D lectin, reflecting their evolutionary trajectory towards a unidirectional respiratory system. In the context of zoonotic infections, how these evolutionary changes affect avian pulmonary surface protection is not clear.

Protein-Protein Interaction between Surfactant Protein D and DC-SIGN via C-Type Lectin Domain Can Suppress HIV-1 Transfer

Surfactant protein D (SP-D) is a soluble C-type lectin, belonging to the collectin (collagen-containing calcium-dependent lectin) family, which acts as an innate immune pattern recognition molecule in the lungs at other mucosal surfaces. Immune regulation and surfactant homeostasis are salient functions of SP-D. SP-D can bind to a range of viral, bacterial, and fungal pathogens and trigger clearance mechanisms. SP-D binds to gp120, the envelope protein expressed on HIV-1, through its C-type lectin or carbohydrate recognition domain. This is of importance since SP-D is secreted by human mucosal epithelial cells and is present in the female reproductive tract, including vagina. Another C-type lectin, dendritic cell (DC)-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), present on the surface of the DCs, also binds to HIV-1 gp120 and facilitates viral transfer to the lymphoid tissues. DCs are also present at the site of HIV-1 entry, embedded in vaginal or rectal mucosa. In the present study, we report a direct protein-protein interaction between recombinant forms of SP-D (rfhSP-D) and DC-SIGN via their C-type lectin domains. Both SP-D and DC-SIGN competed for binding to immobilized HIV-1 gp120. Pre-incubation of human embryonic kidney cells expressing surface DC-SIGN with rfhSP-D significantly inhibited the HIV-1 transfer to activated peripheral blood mononuclear cells. In silico analysis revealed that SP-D and gp120 may occupy same sites on DC-SIGN, which may explain the reduced transfer of HIV-1. In summary, we demonstrate, for the first time, that DC-SIGN is a novel binding partner of SP-D, and this interaction can modulate HIV-1 capture and transfer to CD4⁺ T cells. In addition, the present study also reveals a novel and distinct mechanism of host defense by SP-D against HIV-1.

Purification of surfactant protein D (SP-D) from pooled amniotic fluid and bronchoalveolar lavage

Surfactant protein SP-D is a multimeric collagenous lectin, called collectin. SP-D is a multifunctional, pattern recognition innate immune molecule, which binds in a calcium dependent manner to an array of carbohydrates and lipids, thus offering resistance to invading pathogens, allergen challenge, and pulmonary inflammation. SP-D is predominantly found in the endoplasmic reticulum of type 2 pneumocytes and in the secretory granules of Clara or non-ciliated bronchiolar cells. The highest expression of SP-D is observed in the distal airways and alveoli. There is also an extra pulmonary existence of SP-D. The common sources of native full-length human SP-D are bronchoalveolar lavage (BAL) washings from normal or preferably patients suffering from alveolar proteinosis who overproduce SP-D in the lungs. Amniotic fluid collected at the term during parturition is another reasonable source. Here, we describe a simple and rapid method of purifying native SP-D away from SP-A which is also present in the same source. We also describe procedures of expressing and purifying a recombinant fragment of human SP-D (rhSP-D) comprising trimeric neck and carbohydrate recognition domains that has been shown to have therapeutic effects in murine models of allergy and infection.

Novel roles for complement receptors in T cell regulation and beyond

Complement receptors are expressed on cells of the innate and the adaptive immune system. They play important roles in pathogen and danger sensing as they translate the information gathered by complement fluid phase sensors into cellular responses. Further, they control complement activation on viable and apoptotic host cells, clearance of immune complexes and mediate opsonophagocytosis. More recently, evidence has accumulated that complement receptors form a complex network with other innate receptors systems such as the Toll-like receptors, the Notch signaling system, IgG Fc receptors and C-type lectin receptors contributing to the benefit and burden of innate and adaptive immune responses in autoimmune and allergic diseases as well as in cancer and transplantation. Here, we will discuss recent developments and emerging concepts of complement receptor activation and regulation with a particular focus on the differentiation, maintenance and contraction of effector and regulatory T cells.

Genetic variant associations of human SP-A and SP-D with acute and chronic lung injury

Pulmonary surfactant, a lipoprotein complex, maintains alveolar integrity and plays an important role in lung host defense, and control of inflammation. Altered inflammatory processes and surfactant dysfunction are well described events that occur in patients with acute or chronic lung disease that can develop secondary to a variety of insults. Genetic variants of surfactant proteins, including single nucleotide polymorphisms, haplotypes, and other genetic variations have been associated with acute and chronic lung disease throughout life in several populations and study groups. The hydrophilic surfactant proteins SP-A and SP-D, also known as collectins, in addition to their surfactant-related functions, are important innate immunity molecules as these, among others, exhibit the ability to bind and enhance clearance of a wide range of pathogens and allergens. This review focuses on published association studies of human surfactant proteins A and D genetic polymorphisms with respiratory, and non-respiratory diseases in adults, children, and newborns. The potential role of genetic variations in pulmonary disease or pathogenesis is discussed following an evaluation, and comparison of the available literature.

Dietary supplementation of selenium in inorganic and organic forms differentially and commonly alters blood and liver selenium concentrations and liver gene expression profiles of growing beef heifers

In geographic regions where selenium (Se) soil concentrations are naturally low, the addition of Se to animal feed is necessary. Even though it is known that Se in grass and forage crops is primarily present in organic forms (especially as L-selenomethionine, L-selenocystine, and L-selenocystathionine), the feeding of Se in the naturally occurring organic selenium (OSe) compounds produces higher blood and tissue Se levels than the inorganic Se (ISe) salts, and that animal metabolism of OSe and ISe is fundamentally different. Se is commonly added in inorganic form as sodium selenite to cattle feeds because it is a less expensive source of supplemental Se then are OSe forms. A trial was conducted with growing cattle to determine if the addition of OSe versus ISe forms of Se in beef cattle feed produces differences in hepatic gene expression, thereby gaining insight into the metabolic consequence of feeding OSe versus ISe. Thirty maturing Angus heifers (261 ± 6 days) were fed a corn silage-based diet with no Se supplementation for 75 days. Heifers (body weight = 393 ± 9 kg) then were randomly assigned (n = 10) and fed Se supplements that contained none (control) or 3 mg Se/day in ISe (sodium selenite) or OSe (Sel-Plex®) form and enough of a common cracked corn/cottonseed hull-based diet (0.48 mg Se/day) to support 0.5 kg/day growth for 105 or 106 days. More Se was found in jugular whole blood and red blood cells and biopsied liver tissue of ISe and OSe treatment animals than control animals, and OSe animals contained more Se in these tissues than did ISe. Microarray and bioinformatic analyses of liver tissue gene expression revealed that the content of at least 80 mRNA were affected by ISe or OSe treatments, including mRNA associated with nutrient metabolism; cellular growth, proliferation, and immune response; cell communication or signaling; and tissue/organ development and function. Overall, three Se supplement-dependent gene groups were identified: ISe-dependent, OSe-dependent, and Se form-independent. More specifically, both forms of supplementation appeared to upregulate mitochondrial gene expression capacity, whereas gene expression of a protein involved in antiviral capacity was downregulated in ISe-supplemented animals, and OSe-supplemented animals had reduced levels of mRNA encoding proteins known to be upregulated during oxidative stress and cancerous states.

The angiogenic inhibitor long pentraxin PTX3 forms an asymmetric octamer with two binding sites for FGF2

The inflammation-associated long pentraxin PTX3 plays key roles in innate immunity, female fertility, and vascular biology (e.g. it inhibits FGF2 (fibroblast growth factor 2)-mediated angiogenesis). PTX3 is composed of multiple protomers, each composed of distinct N- and C-terminal domains; however, it is not known how these are organized or contribute to its functional properties. Here, biophysical analyses reveal that PTX3 is composed of eight identical protomers, associated through disulfide bonds, forming an elongated and asymmetric, molecule with two differently sized domains interconnected by a stalk. The N-terminal region of the protomer provides the main structural determinant underlying this quaternary organization, supporting formation of a disulfide-linked tetramer and a dimer of dimers (a non-covalent tetramer), giving rise to the asymmetry of the molecule. Furthermore, the PTX3 octamer is shown to contain two FGF2 binding sites, where it is the tetramers that act as the functional units in ligand recognition. Thus, these studies provide a unifying model of the PTX3 oligomer, explaining both its quaternary organization and how this is required for its antiangiogenic function.

Myeloperoxidase-dependent inactivation of surfactant protein D in vitro and in vivo

Surfactant protein D (SP-D) plays diverse and important roles in innate immunity and pulmonary homeostasis. Neutrophils and myeloperoxidase (MPO) colocalized with SP-D in a murine bacterial pneumonia model of acute inflammation, suggesting that MPO-derived reactive species might alter the function of SP-D. Exposure of SP-D to the complete MPO-H(2)O(2)-halide system caused loss of SP-D-dependent aggregating activity. Hypochlorous acid (HOCl), the major oxidant generated by MPO, caused a similar loss of aggregating activity, which was accompanied by the generation of abnormal disulfide-cross-linked oligomers. A full-length SP-D mutant lacking N-terminal cysteine residues and truncation mutants lacking the N-terminal domains were resistant to the oxidant-induced alterations in disulfide bonding. Mass spectroscopy of HOCl-treated human SP-D demonstrated several modifications, but none involved key ligand binding residues. There was detectable oxidation of cysteine 15, but no HOCl-induced cysteine modifications were observed in the C-terminal lectin domain. Together, the findings localize abnormal disulfide cross-links to the N-terminal domain. MPO-deficient mice showed decreased cross-linking of SP-D and increased SP-D-dependent aggregating activity in the pneumonia model. Thus, MPO-derived oxidants can lead to modifications of SP-D structure with associated alterations in its characteristic aggregating activity.

Modification of surfactant protein D by reactive oxygen-nitrogen intermediates is accompanied by loss of aggregating activity, in vitro and in vivo

Surfactant protein D (SP-D) is an important effector of innate immunity. We have previously shown that SP-D accumulates at sites of acute bacterial infection and neutrophil infiltration, a setting associated with the release of reactive species such as peroxynitrite. Incubation of native SP-D or trimeric SP-D lectin domains (NCRDs) with peroxynitrite resulted in nitration and nondisulfide cross-linking. Modifications were blocked by peroxynitrite scavengers or pH inactivation of peroxynitrite, and mass spectroscopy confirmed nitration of conserved tyrosine residues within the C-terminal neck and lectin domains. Mutant NCRDs lacking one or more of the tyrosines allowed us to demonstrate preferential nitration of Tyr314 and the formation of Tyr228-dependent cross-links. Although there was no effect of peroxynitrite or tyrosine mutations on lectin activity, incubation of SP-D dodecamers or murine lavage with peroxynitrite decreased the SP-D-dependent aggregation of lipopolysaccharide-coated beads, supporting our hypothesis that defective aggregation results from abnormal cross-linking. We also observed nitration, cross-linking of SP-D, and a significant decrease in SP-D-dependent aggregating activity in the lavage of mice acutely exposed to nitrogen dioxide. Thus, modification of SP-D by reactive oxygen-nitrogen species could contribute to alterations in the structure and function of SP-D at sites of inflammation in vivo.

Lung surfactant proteins A and D as pattern recognition proteins

Lung surfactant proteins A and D belong to a group of soluble humoral pattern recognition receptors, called collectins, which modulate the immune response to microorganisms. They bind essential carbohydrate and lipid antigens found on the surface of microorganisms via low affinity C-type lectin domains and regulate the host's response by binding to immune cell surface receptors. They form multimeric structures that bind, agglutinate, opsonise and neutralize many different pathogenic microorganisms including bacteria, yeast, fungi and viruses. They modulate the uptake of these microorganisms by phagocytic cells as well as both the inflammatory and the adaptive immune responses. Recent data have also highlighted their involvement in clearance of apoptotic cells, hypersensitivity and a number of lung diseases.

Structural characterization of PTX3 disulfide bond network and its multimeric status in cumulus matrix organization

PTX3 is an acute phase glycoprotein that plays key roles in resistance to certain pathogens and in female fertility. PTX3 exerts its functions by interacting with a number of structurally unrelated molecules, a capacity that is likely to rely on its complex multimeric structure stabilized by interchain disulfide bonds. In this study, PAGE analyses performed under both native and denaturing conditions indicated that human recombinant PTX3 is mainly composed of covalently linked octamers. The network of disulfide bonds supporting this octameric assembly was resolved by mass spectrometry and Cys to Ser site-directed mutagenesis. Here we report that cysteine residues at positions 47, 49, and 103 in the N-terminal domain form three symmetric interchain disulfide bonds stabilizing four protein subunits in a tetrameric arrangement. Additional interchain disulfide bonds formed by the C-terminal domain cysteines Cys(317) and Cys(318) are responsible for linking the PTX3 tetramers into octamers. We also identified three intrachain disulfide bonds within the C-terminal domain that we used as structural constraints to build a new three-dimensional model for this domain. Previously it has been shown that PTX3 is a key component of the cumulus oophorus extracellular matrix, which forms around the oocyte prior to ovulation, because cumuli from PTX3(-/-) mice show defective matrix organization. Recombinant PTX3 is able to restore the normal phenotype ex vivo in cumuli from PTX3(-/-) mice. Here we demonstrate that PTX3 Cys to Ser mutants, mainly assembled into tetramers, exhibited wild type rescue activity, whereas a mutant, predominantly composed of dimers, had impaired functionality. These findings indicate that protein oligomerization is essential for PTX3 activity within the cumulus matrix and implicate PTX3 tetramers as the functional molecular units required for cumulus matrix organization and stabilization.

Surfactant proteins SP-A and SP-D: structure, function and receptors

Surfactant proteins, SP-A and SP-D, are collagen-containing C-type (calcium dependent) lectins called collectins, which contribute significantly to surfactant homeostasis and pulmonary immunity. These highly versatile innate immune molecules are involved in a range of immune functions including viral neutralization, clearance of bacteria, fungi and apoptotic and necrotic cells, down regulation of allergic reaction and resolution of inflammation. Their basic structures include a triple-helical collagen region and a C-terminal homotrimeric lectin or carbohydrate recognition domain (CRD). The trimeric CRDs can recognize carbohydrate or charge patterns on microbes, allergens and dying cells, while the collagen region can interact with receptor molecules present on a variety of immune cells in order to initiate clearance mechanisms. Studies involving gene knock-out mice, murine models of lung hypersensitivity and infection, and functional characterization of cell surface receptors have revealed the diverse roles of SP-A and SP-D in the control of lung inflammation. A recently proposed model based on studies with the calreticulin-CD91 complex as a receptor for SP-A and SP-D has suggested an anti-inflammatory role for SP-A and SP-D in naïve lungs which would help minimise the potential damage that continual low level exposure to pathogens, allergens and apoptosis can cause. However, when the lungs are overwhelmed with exogenous insults, SP-A and SP-D can assume pro-inflammatory roles in order to complement pulmonary innate and adaptive immunity. This review is an update on the structural and functional aspects of SP-A and SP-D, with emphasis on their roles in controlling pulmonary infection, allergy and inflammation. We also try to put in perspective the controversial subject of the candidate receptor molecules for SP-A and SP-D.

Susceptibility of mice genetically deficient in the surfactant protein (SP)-A or SP-D gene to pulmonary hypersensitivity induced by antigens and allergens of Aspergillus fumigatus

Lung surfactant protein A (SP-A) and D (SP-D) are innate immune molecules which are known to interact with allergens and immune cells and modulate cytokine and chemokine profiles during host hypersensitivity response. We have previously shown therapeutic effects of SP-A and SP-D using a murine model of lung hypersensitivity to Aspergillus fumigatus (Afu) allergens. In this study, we have examined the susceptibility of SP-A (AKO) or SP-D gene-deficient (DKO) mice to the Afu allergen challenge, as compared with the wild-type mice. Both AKO and DKO mice exhibited intrinsic hypereosinophilia and several-fold increase in levels of IL-5 and IL-13, and lowering of IFN-gamma to IL-4 ratio in the lungs, suggesting a Th2 bias of immune response. This Th2 bias was reversible by treating AKO or DKO mice with SP-A or SP-D, respectively. The AKO and DKO mice showed distinct immune responses to Afu sensitization. DKO mice were found more susceptible than wild-type mice to pulmonary hypersensitivity induced by Afu allergens. AKO mice were found to be nearly resistant to Afu sensitization. Intranasal treatment with SP-D or rhSP-D (a recombinant fragment of human SP-D containing trimeric C-type lectin domains) was effective in rescuing the Afu-sensitized DKO mice, while SP-A-treated Afu-sensitized AKO mice showed several-fold elevated levels of IL-13 and IL-5, resulting in increased pulmonary eosinophilia and damaged lung tissue. These data reaffirm an important role for SP-A and SP-D in offering resistance to pulmonary allergenic challenge.

Ligand specificity of human surfactant protein D: expression of a mutant trimeric collectin that shows enhanced interactions with influenza A virus

Surfactant protein D is a pattern recognition molecule that plays diverse roles in immune regulation and anti-microbial host defense. Its interactions with known ligands are calcium-dependent and involve binding to the trimeric, C-type carbohydrate recognition domain. Surfactant protein D preferentially binds to glucose and related sugars. However, CL-43, a bovine serum lectin, which evolved through duplication of the surfactant protein D gene in ruminants, prefers mannose and mannose-rich polysaccharides. Surfactant protein D is characterized by two relatively conserved motifs at the binding face, along the edges of the shallow carbohydrate-binding groove. For CL-43, sequence alignments demonstrate a basic insertion, Arg-Ala-Lys (RAK), immediately N-terminal to the first motif. We hypothesized that this insertion contributes to the differences in saccharide selectivity and host defense function and compared the activities of recombinant trimeric neck + carbohydrate recognition domains of human surfactant protein D (NCRD) with CL-43 (RCL-43-NCRD) and selected NCRD mutants. Insertion of the CL-43 RAK sequence or a control Ala-Ala-Ala sequence (AAA) into the corresponding position in NCRD increased the efficiency of binding to mannan and changed the inhibitory potencies of competing saccharides to more closely resemble those of CL-43. In addition, RAK resembled CL-43 in its greater capacity to inhibit the infectivity of influenza A virus and to increase uptake of influenza by neutrophils.

Neutrophil Serine Proteinases Inactivate Surfactant Protein D by Cleaving within a Conserved Subregion of the Carbohydrate Recognition Domain

Surfactant protein D (SP-D) plays important roles in innate immunity including the defense against bacteria, fungi, and respiratory viruses. Because SP-D specifically interacts with neutrophils that infiltrate the lung in response to acute inflammation and infection, we examined the hypothesis that the neutrophil-derived serine proteinases (NSPs): neutrophil elastase, proteinase-3, and cathepsin G degrade SP-D. All three human NSPs specifically cleaved recombinant rat and natural human SP-D dodecamers in a time- and dose-dependent manner, which was reciprocally dependent on calcium concentration. The NSPs generated similar, relatively stable, disulfide cross-linked immunoreactive fragments of approximately 35 kDa (reduced), and sequencing of a major catheptic fragment definitively localized the major sites of cleavage to a highly conserved subregion of the carbohydrate recognition domain. Cleavage markedly reduced the ability of SP-D to promote bacterial aggregation and to bind to yeast mannan in vitro. Incubation of SP-D with isolated murine neutrophils led to the generation of similar fragments, and cleavage was inhibited with synthetic and natural serine proteinase inhibitors. In addition, neutrophils genetically deficient in neutrophil elastase and/or cathepsin G were impaired in their ability to degrade SP-D. Using a mouse model of acute bacterial pneumonia, we observed the accumulation of SP-D at sites of neutrophil infiltration coinciding with the appearance of approximately 35-kDa SP-D fragments in bronchoalveolar lavage fluids. Together, our data suggest that neutrophil-derived serine proteinases cleave SP-D at sites of inflammation with potential deleterious effects on its biological functions.

The Application of Recombinant Human Collagen in Tissue Engineering

Collagen is the main structural protein in vertebrates. It plays an essential role in providing a scaffold for cellular support and thereby affecting cell attachment, migration, proliferation, differentiation, and survival. As such, it also plays an important role in numerous approaches to the engineering of human tissues for medical applications related to tissue, bone, and skin repair and reconstruction. Currently, the collagen used in tissue engineering applications is derived from animal tissues, creating concerns related to the quality, purity, and predictability of its performance. It also carries the risk of transmission of infectious agents and precipitating immunological reactions. The recent development of recombinant sources of human collagen provides a reliable, predictable and chemically defined source of purified human collagens that is free of animal components. The triple-helical collagens made by recombinant technology have the same amino acid sequence as human tissue-derived collagen. Furthermore, by achieving the equivalent extent of proline hydroxylation via coexpression of genes encoding prolyl hydroxylase with the collagen genes, one can produce collagens with a similar degree of stability as naturally occurring material. The recombinant production process of collagen involves the generation of single triple-helical molecules that are then used to construct more complex three-dimensional structures. If one loosely defines tissue engineering as the use of a biocompatible scaffold combined with a biologically active agent (be it a gene or gene construct, growth factor or other biologically active agent) to induce tissue regeneration, then the production of recombinant human collagen enables the engineering of human tissue based on a human matrix or scaffold. Recombinant human collagens are an efficient scaffold for bone repair when combined with a recombinant bone morphogenetic protein in a porous, sponge-like format, and when presented as a membrane, sponge or gel can serve as a basis for the engineering of skin, cartilage and periodontal ligament, depending on the specific requirements of the chosen application.

Expression and secretion of ficolin beta by porcine neutrophils

Ficolins are collagenous lectins that bind N-acetylglucosamine (GlcNAc) as well as some bacterial surfaces, and may have opsonic and complement-activating functions. Ficolin alpha in porcine plasma binds Actinobacillus pleuropneumoniae serotype 5 (APP) in a GlcNAc-dependent manner. In the present study, we discovered that porcine neutrophils, but not platelets or mononuclear cells, contained a different ficolin that migrated as a 39-kDa band on SDS-PAGE and resembled a minor component of plasma ficolins that binds APP. However, neutrophil ficolins (pI range 6.4-7.4) were readily distinguished from plasma ficolin alpha (pI 5.2-5.8) by 2D PAGE. Neutrophil ficolin was consistent with ficolin beta by pI and peptide mass fingerprinting with matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Porcine neutrophils expressed ficolin beta, but not ficolin alpha, as determined by RT-PCR. Ficolin beta was present in the membrane and cytoplasmic fractions of nonactivated neutrophils, but the majority of ficolin beta was secreted upon activation with PMA. Ficolin alpha readily bound to intact APP, but ficolin beta did not under the same conditions. These studies demonstrate that neutrophils express ficolin beta and secrete it when activated; however, ficolin beta may have different binding functions than ficolin alpha.

Protective effects of a recombinant fragment of human surfactant protein D in a murine model of pulmonary hypersensitivity induced by dust mite allergens

Lung surfactant protein D (SP-D) is a carbohydrate pattern recognition immune molecule. It can interact with a range of pathogens, stimulate immune cells and manipulate cytokine profiles during host's immune response. SP-D has also been shown to interact, via its carbohydrate recognition domains, with glycoprotein allergens of house dust mite (Dermatophagoides pteronyssinus, Derp), inhibiting specific IgE isolated from mite-sensitive asthmatic patients from binding these allergens, and blocking subsequent histamine release from sensitized basophils. In the present study, we have examined the protection offered by various doses of intranasal administration of a recombinant fragment of human SP-D (rhSP-D) in a murine model of pulmonary hypersensitivity to Derp allergens which showed characteristic high levels of specific IgE antibodies, peripheral blood eosinophilia, pulmonary infiltrates and a Th2 cytokine response. Treatment of Derp mice with rhSP-D led to significant reduction in Derp-specific IgE levels, blood eosinophilia and pulmonary cellular infiltration. The levels of IL-4 and IL-5 were decreased, while those of IL-12 and IFN-gamma were raised in the supernatant of the cultured splenocytes, indicating a Th2 to Th1 polarization. These results suggest that SP-D has a protective role in the modulation of allergic sensitization and in the development of allergic reactions to Derp allergens and highlight potential of the rhSP-D as a therapeutic for pulmonary hypersensitivity.