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.     

Surfactant Protein D Inhibits HIV-1 Infection of Target Cells via Interference with gp120-CD4 Interaction and Modulates Pro-Inflammatory Cytokine Production

Surfactant Protein SP-D, a member of the collectin family, is a pattern recognition protein, secreted by mucosal epithelial cells and has an important role in innate immunity against various pathogens. In this study, we confirm that native human SP-D and a recombinant fragment of human SP-D (rhSP-D) bind to gp120 of HIV-1 and significantly inhibit viral replication in vitro in a calcium and dose-dependent manner. We show, for the first time, that SP-D and rhSP-D act as potent inhibitors of HIV-1 entry in to target cells and block the interaction between CD4 and gp120 in a dose-dependent manner. The rhSP-D-mediated inhibition of viral replication was examined using three clinical isolates of HIV-1 and three target cells: Jurkat T cells, U937 monocytic cells and PBMCs. HIV-1 induced cytokine storm in the three target cells was significantly suppressed by rhSP-D. Phosphorylation of key kinases p38, Erk1/2 and AKT, which contribute to HIV-1 induced immune activation, was significantly reduced in vitro in the presence of rhSP-D. Notably, anti-HIV-1 activity of rhSP-D was retained in the presence of biological fluids such as cervico-vaginal lavage and seminal plasma. Our study illustrates the multi-faceted role of human SP-D against HIV-1 and potential of rhSP-D for immunotherapy to inhibit viral entry and immune activation in acute HIV infection.     

Human Surfactant Protein D Alters Oxidative Stress and HMGA1 Expression to Induce p53 Apoptotic Pathway in Eosinophil Leukemic Cell Line

Surfactant protein D (SP-D), an innate immune molecule, has an indispensable role in host defense and regulation of inflammation. Immune related functions regulated by SP-D include agglutination of pathogens, phagocytosis, oxidative burst, antigen presentation, T lymphocyte proliferation, cytokine secretion, induction of apoptosis and clearance of apoptotic cells. The present study unravels a novel ability of SP-D to reduce the viability of leukemic cells (eosinophilic leukemic cell line, AML14.3D10; acute myeloid leukemia cell line, THP-1; acute lymphoid leukemia cell lines, Jurkat, Raji; and human breast epithelial cell line, MCF-7), and explains the underlying mechanisms. SP-D and a recombinant fragment of human SP-D (rhSP-D) induced G2/M phase cell cycle arrest, and dose and time-dependent apoptosis in the AML14.3D10 eosinophilic leukemia cell line. Levels of various apoptotic markers viz. activated p53, cleaved caspase-9 and PARP, along with G2/M checkpoints (p21 and Tyr15 phosphorylation of cdc2) showed significant increase in these cells. We further attempted to elucidate the underlying mechanisms of rhSP-D induced apoptosis using proteomic analysis. This approach identified large scale molecular changes initiated by SP-D in a human cell for the first time. Among others, the proteomics analysis highlighted a decreased expression of survival related proteins such as HMGA1, overexpression of proteins to protect the cells from oxidative burst, while a drastic decrease in mitochondrial antioxidant defense system. rhSP-D mediated enhanced oxidative burst in AML14.3D10 cells was confirmed, while antioxidant, N-acetyl-L-cysteine, abrogated the rhSP-D induced apoptosis. The rhSP-D mediated reduced viability was specific to the cancer cell lines and viability of human PBMCs from healthy controls was not affected. The study suggests involvement of SP-D in host’s immunosurveillance and therapeutic potential of rhSP-D in the eosinophilic leukemia and cancers of other origins.     

Surfactant protein D attenuates nitric oxide-stimulated apoptosis in rat chondrocyte by suppressing p38 MAPK signaling

Innate immune molecule surfactant protein D (SP-D), a member of the C-type lectin protein family, plays an indispensable role in host defense and the regulation of inflammation in the lung and other tissues. Osteoarthritis (OA) is a degenerative disease of cartilage, with inflammation that causes pathologic changes and tissue damage. However, it is unknown whether there exist SP-D expression and its potential role in the pathogenesis of OA. In this study, we examined SP-D expression and explored its biological function in a sodium nitroprusside (SNP)-stimulated rat chondrocytes and surgically-induced rat OA model. We found SP-D expression in both human and rat articular chondrocytes, with higher level in normal chondrocytes compared to in OA chondrocytes. Furthermore, In vivo study demonstrated that recombinant human SP-D (rhSP-D) ameliorated cartilage degeneration in surgically-induced rat OA model. In vitro cell culture study showed that rhSP-D markedly inhibited the expression of caspase-3 as an apoptosis biomarker, and decreased phosphorylation of p38 mitogen-activated protein kinase (MAPK), which resulted in maintaining normal nuclear morphology and increasing mitochondrial membrane potential in SNP-stimulated rat chondrocytes. Collectively, these findings indicate that SP-D expresses in articular chondrocytes and suppresses SNP-stimulated chondrocyte apoptosis and ameliorates cartilage degeneration via suppressing p38 MAPK activity.     

Pulmonary surfactant proteins A and D directly suppress CD3+/CD4+ cell function: evidence for two shared mechanisms

Pulmonary surfactant is a lipoprotein complex that lowers surface tension at the air-liquid interface of the lung and participates in pulmonary host defense. Surfactant proteins (SP), SP-A and SP-D, modulate a variety of immune cell functions, including the production of cytokines and free radicals. Previous studies showed that SP-A and SP-D inhibit lymphocyte proliferation in the presence of accessory cells. The goal of this study was to determine whether SP-A and SP-D directly suppress Th cell function. Both proteins inhibited CD3(+)/CD4(+) lymphocyte proliferation induced by PMA and ionomycin in an IL-2-independent manner. Both proteins decreased the number of cells entering the S and mitotic phases of the cell cycle. Neither SP-A nor SP-D altered cell viability, apoptosis, or secretion of IL-2, IL-4, or IFN-gamma when Th cells were treated with PMA and ionomycin. However, both proteins attenuated ionomycin-induced cytosolic free calcium ([Ca(2+) ](i)), but not thapsigargin-induced changes in [Ca(2+)](i). In summary, inhibition of T cell proliferation by SP-A and SP-D occurs via two mechanisms, an IL-2-dependent mechanism observed with accessory cell-dependent T cell mitogens and specific Ag, as well as an IL-2-independent mechanism of suppression that potentially involves attenuation of [Ca(2+)](i).     

Surfactant proteins A and D in Eustachian tube epithelium

Surfactant protein (SP) A and SP-D are collectins that have roles in host defense. The Eustachian tube (ET) maintains the patency between the upper airways and the middle ear. Dysfunction of local mucosal immunity in ET may predispose infants to recurrent otitis media. We recently described preliminary evidence of the expression of SP-A and SP-D in the ET. Our present aim was to establish the sites of SP-A and SP-D expression within the epithelium of the ET in vivo. With in situ hybridization, electron microscopy, and immunoelectron microscopy, the cells responsible for SP-A and SP-D expression and storage were identified. SP-A expression was localized within the ET epithelium, and the protein was found in the electron-dense granules of microvillar epithelial cells. Being concentrated in the epithelial lining, only a few cells revealed intracellular SP-D, and it was not associated with granules. The SP-A and SP-D immunoreactivities in ET lavage fluid, as shown by Western blot analyses, were similar to those in bronchoalveolar lavage fluid. We propose that there are specialized cells in the ET epithelium expressing and secreting SP-A and SP-D. SP-A and SP-D may be important for antibody-independent protection of the middle ear against infections.     

Evolution of the lung surfactant proteins in birds and mammals

Phylogenetic analyses of the families of mammalian lung surfactant proteins (SP-A, SP-B, SP-C, and SP-D) supported the hypothesis that these proteins have diverged between birds and mammals as a result of lineage-specific gene duplications and deletions. Homologs of mammalian genes encoding SP-B, SP-C, and SP-D appear to have been deleted in chickens, whereas there was evidence of avian-specific duplications of the genes encoding SP-A and presaposin. Analysis of the genes closely linked to human SP-B, SP-C, and SP-D genes revealed that all three of these genes are closely linked to genes having orthologs on chicken chromosome 6 and also to genes lacking chicken orthologs. These relationships suggest that all of the lung surfactant protein genes, as well as certain related genes, may have been linked in the ancestor of humans and chickens. Further, they imply that the loss of surfactant protein genes in the avian lineages formed part of major genomic rearrangement events that involved the loss of other genes as well. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Surfactant proteins A and D bind CD14 by different mechanisms

Surfactant proteins A (SP-A) and D (SP-D) are lung collectins that are constituents of the innate immune system of the lung. Recent evidence (Sano, H., Sohma, H., Muta, T., Nomura, S., Voelker, D. R., and Kuroki, Y. (1999) J. Immunol. 163, 387-395) demonstrates that SP-A modulates lipopolysaccharide (LPS)-induced cellular responses by direct interaction with CD14. In this report we examined the structural elements of the lung collectins involved in CD14 recognition and the consequences for CD14/LPS interaction. Rat SP-A and SP-D bound CD14 in a concentration-dependent manner. Mannose and EDTA inhibited SP-D binding to CD14 but did not decrease SP-A binding. The SP-A binding to CD14 was completely blocked by a monoclonal antibody that binds to the SP-A neck domain but only partially blocked by an antibody that binds to the SP-A lectin domain. SP-A but not SP-D bound to deglycosylated CD14. SP-D decreased CD14 binding to both smooth and rough LPS, whereas SP-A enhanced CD14 binding to rough LPS and inhibited binding to smooth LPS. SP-A also altered the migration profile of LPS on a sucrose density gradient in the presence of CD14. From these results, we conclude that 1) lung collectins bind CD14, 2) the SP-A neck domain and SP-D lectin domain participate in CD14 binding, 3) SP-A recognizes a peptide component and SP-D recognizes a carbohydrate moiety of CD14, and 4) lung collectins alter LPS/CD14 interactions.     

Serum surfactant protein D is increased in acute and chronic inflammation in mice

Surfactant protein A (SP-A) and surfactant protein D (SP-D) are important components of innate immunity that can modify the inflammatory response. However, alterations and regulation of SP-A and SP-D in acute and chronic inflammation are not well defined. In addition, serum SP-D may serve as a biomarker of lung inflammation. We determined the expression of SP-A and SP-D in murine models. To study acute inflammation, we instilled bleomycin intrabronchially. To study chronic lung inflammation, we used a transgenic mouse that overexpresses tumor necrosis factor (TNF)-alpha under the control of the SP-C promoter. These mice have a chronic mononuclear cell infiltration, airspace enlargement, pulmonary hypertension, and focal pulmonary fibrosis. In acute inflammation model, levels of mRNA for all surfactant proteins were reduced after bleomycin administration. However, serum SP-D was increased from days 7 to 28 after instillation. In chronic inflammation model, SP-D mRNA expression was increased, whereas the expression of SP-A, SP-B and SP-C was reduced. Both serum and lung SP-D concentrations were increased in chronic lung inflammation. These data clarified profile of SP-A and SP-D in acute and chronic inflammation and indicated that serum SP-D can serve as a biomarker of lung inflammation in both acute and chronic lung injury in mice.     

Surfactant protein A and D in the reproductive tract of stallion

The presence of surface-active material in the lung alveolus has been known for several decades as being essential for normal lung function. The host defense and controlling inflammatory processes of the lung are the major functions of SP-A and SP-D. SP-A and SP-D were originally demonstrated in alveolar type II cells, but recent studies have shown extrapulmonary expression of SP-A and SP-D indicating systemic roles of these proteins. Present study describes the presence of SP-A and SP-D in the stallion genital tract, prepuce, prostate, testis, and seminal vesicle using Western blotting and immunohistochemistry. This paper presents the first evidence for the existence of SP-A and SP-D glycoproteins in the stallion genital tract. We examined genital system organs and tissues from stallion and were able to show that surfactant protein A and D reactive with surfactant-specific antibodies were present in the stallion genital tract tissues and organs. On the basis of results, it can be postulated that surfactant proteins in the stallion reproductive tract contribute to the immune surveillance and to active barrier defense mechanism.     

Nanoparticles modulate surfactant protein A and D mediated protection against influenza A infection in vitro

Numerous epidemiological and toxicological studies have indicated that respiratory infections are exacerbated following enhanced exposure to airborne particulates. Surfactant protein A (SP-A) and SP-D form an important part of the innate immune response in the lung and can interact with nanoparticles to modulate the cellular uptake of these particles. We hypothesize that this interaction will also affect the ability of these proteins to combat infections. TT1, A549 and differentiated THP-1 cells, representing the predominant cell types found in the alveolus namely alveolar type I (ATI) epithelial cells, ATII cells and macrophages, were used to examine the effect of two model nanoparticles, 100 nm amine modified (A-PS) and unmodified polystyrene (U-PS), on the ability of SP-A and SP-D to neutralize influenza A infections in vitro. Pre-incubation of low concentrations of U-PS with SP-A resulted in a reduction of SP-A anti-influenza activity in A549 cells, whereas at higher concentrations there was an increase in SP-A antiviral activity. This differential pattern of U-PS concentration on surfactant protein mediated protection against IAV was also shown with SP-D in TT1 cells. On the other hand, low concentrations of A-PS particles resulted in a reduction of SP-A activity in TT1 cells and a reduction in SP-D activity in A549 cells. These results indicate that nanoparticles can modulate the ability of SP-A and SP-D to combat viral challenges. Furthermore, the nanoparticle concentration, surface chemistry and cell type under investigation are important factors in determining the extent of these modulations.     

Pulmonary collectins enhance phagocytosis of Mycobacterium avium through increased activity of mannose receptor

Collectins, including surfactant proteins A (SP-A) and D (SP-D) and mannose binding lectin (MBL), are the important constituents of the innate immune system. Mycobacterium avium, a facultative intracellular pathogen, has developed numerous mechanisms for entering mononuclear phagocytes. In this study, we investigated the interactions of collectins with M. avium and the effects of these lectins on phagocytosis of M. avium by macrophages. SP-A, SP-D, and MBL exhibited a concentration-dependent binding to M. avium. The binding of SP-A to M. avium was Ca(2+)-dependent but that of SP-D and MBL was Ca(2+)-independent. SP-A and SP-D but not MBL enhanced the phagocytosis of FITC-labeled M. avium by rat alveolar macrophages and human monocyte-derived macrophages. Excess mannan, zymosan, and lipoarabinomannan derived from the M. avium-intracellular complex, significantly decreased the collectin-stimulated phagocytosis of M. avium. Enhanced phagocytosis was not affected by the presence of cycloheximide or chelation of Ca(2+). The mutated collectin, SP-A(E195Q, R197D) exhibited decreased binding to M. avium but stimulated phagocytosis to a level comparable to wild-type SP-A. Enhanced phagocytosis by cells persisted even after preincubation and removal of SP-A or SP-D. Rat alveolar macrophages that had been incubated with SP-A or SP-D also exhibited enhanced uptake of (125)I-mannosylated BSA. Analysis by confocal microscopy and flow cytometry revealed that the lung collectins up-regulated the cell surface expression of mannose receptor on monocyte-derived macrophages. These results provide compelling evidence that SP-A and SP-D enhance mannose receptor-mediated phagocytosis of M. avium by macrophages.     

Immunodetection of surfactant proteins in human organ of Corti, Eustachian tube and kidney

The presence of surfactant proteins was investigated in the human organ of Corti, Eustachian tube and kidney tissues. It has previously been shown that lamellar bodies are present in hairy cells of organ of Corti, in the cytoplasm of secretory and lumen of tubal glands of Eustachian tube and kidney renal basement membrane. No evidence for the presence of surfactant proteins in the organ of Corti and kidney has been presented until now. The aim of this study was to find out if surfactant proteins were expressed in other epithelia such as organ of Corti, Eustachian tube and kidney. Surfactant proteins were identified using one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. On one-dimensional Western blots, bands for surfactant protein A in human Eustachian tube (SP-A, 34 kDa) and in kidney extracts, and for surfactant protein D (SP-D, 43 kDa) in Eustachian tube and in kidney extracts (SP-D, 86 kDa), and for surfactant protein B (SP-B, 8 kDa) in human Eustachian tube and organ of Corti extracts were detected. Bands corresponded to monomeric forms of lung surfactant proteins. These results indicate the presence of SP-A and SP-D in kidney epithelium, SP-A, SP-B and SP-D in Eustachian tube and SP-B in the organ of Corti.     

By binding SIRPalpha or calreticulin/CD91, lung collectins act as dual function surveillance molecules to suppress or enhance inflammation

Surfactant proteins A and D (SP-A and SP-D) are lung collectins composed of two regions, a globular head domain that binds PAMPs and a collagenous tail domain that initiates phagocytosis. We provide evidence that SP-A and SP-D act in a dual manner, to enhance or suppress inflammatory mediator production depending on binding orientation. SP-A and SP-D bind SIRPalpha through their globular heads to initiate a signaling pathway that blocks proinflammatory mediator production. In contrast, their collagenous tails stimulate proinflammatory mediator production through binding to calreticulin/CD91. Together a model is implied in which SP-A and SP-D help maintain a non/anti-inflammatory lung environment by stimulating SIRPalpha on resident cells through their globular heads. However, interaction of these heads with PAMPs on foreign organisms or damaged cells and presentation of the collagenous tails in an aggregated state to calreticulin/CD91, stimulates phagocytosis and proinflammatory responses.     

Sequential targeted deficiency of SP-A and -D leads to progressive alveolar lipoproteinosis and emphysema

Surfactant proteins-A and -D (SP-A and SP-D) are members of the collectin protein family. Mice singly deficient in SP-A and SP-D have distinct phenotypes. Both have altered inflammatory responses to microbial challenges. To further investigate the functions of SP-A and SP-D in vivo, we developed mice deficient in both proteins by sequentially targeting the closely linked genes in embryonic stem cells using graded resistance to G-418. There is a progressive increase in bronchoalveolar lavage phospholipid, protein, and macrophage content through 24 wk of age. The macrophages from doubly deficient mice express high levels of the matrix metalloproteinase MMP-12 and develop intense but patchy lung inflammation. Stereological analysis demonstrates significant air space enlargement and reduction in alveolar septal tissue per unit volume, consistent with emphysema. These changes qualitatively resemble the lung pathology seen in SP-D-deficient mice. These doubly deficient mice will be useful in dissecting the potential overlap in function between SP-A and SP-D in host defense.     

Characterization of pulmonary surfactant protein D: its copurification with lipids

Surfactant protein D (SP-D) is a collagenous surfactant associated protein synthesized by alveolar type II cells. SP-D was purified from the supernatant of rat bronchoalveolar lavage fluids obtained by centrifugation at 33,000 x gav for 16 h. The contents of SP-D and SP-A in fractions obtained by the centrifugation of rat bronchoalveolar lavage were determined by enzyme-linked immunoassay. The total content of SP-D was approximately 12% of that of SP-A in these lavage fluids. 99.1% of SP-A was present in the 33,000g pellet, whereas 71.1% of SP-D was in the 33,000g supernatant. Analysis by high performance liquid chromatography reveals that lipids are copurified with isolated SP-D. Phosphatidylcholine accounted for 84.8% of the phospholipids copurified with SP-D. Unlike SP-A, SP-D in the purified and delipidated form failed to compete with 125I-labeled SP-A for phosphatidylcholine binding, and to aggregate phospholipid liposomes. The present study demonstrates that lipids are copurified with SP-D, that SP-D and SP-A distribute differently in rat bronchoalveolar lavage fluids, and that SP-D in the purified and delipidated form does not exhibit interaction with lipids in the same fashion as SP-A.     

Pulmonary Collectins Protect Macrophages against Pore-forming Activity of Legionella pneumophila and Suppress Its Intracellular Growth

Pulmonary collectins, surfactant proteins A (SP-A) and D (SP-D), play important roles in innate immunity of the lung. Legionella pneumophila is a bacterial respiratory pathogen that can replicate within macrophages and causes opportunistic infections. L. pneumophila possesses cytolytic activity, resulting from insertion of pores in the macrophage membrane upon contact. We examined whether pulmonary collectins play protective roles against L. pneumophila infection. SP-A and SP-D bound to L. pneumophila and its lipopolysaccharide (LPS) and inhibited the bacterial growth in a Ca²⁺-dependent manner. The addition of LPS in the culture blocked the inhibitory effects on L. pneumophila growth by the collectins, indicating the importance of LPS-collectin interaction. When differentiated THP-1 cells were infected with L. pneumophila in the presence of SP-A and SP-D, the number of permeable cells was significantly decreased, indicating that pulmonary collectins inhibit pore-forming activity of L. pneumophila. The number of live bacteria within the macrophages on days 1–4 after infection was significantly decreased when infection was performed in the presence of pulmonary collectins. The phagocytosis experiments with the pH-sensitive dye-labeled bacteria revealed that pulmonary collectins promoted bacterial localization to an acidic compartment. In addition, SP-A and SP-D significantly increased the number of L. pneumophila co-localized with LAMP-1. These results indicate that pulmonary collectins protect macrophages against contact-dependent cytolytic activity of L. pneumophila and suppress intracellular growth of the phagocytosed bacteria. The promotion of lysosomal fusion with Legionella-containing phagosomes constitutes a likely mechanism of L. pneumophila growth suppression by the collectins.     

支原体肺炎患者治疗后血清SP-A、SP-D与hs-CRP的变化趋势及临床意义

目的:研究支原体肺炎(MP)患者血清肺表面活性蛋白-A(SP-A)、肺表面活性蛋白-D(SP-D)与超敏C反应蛋白(hs-CRP)的变化趋势及临床意义。方法:选择从2015年9月到2016年9月在我院治疗的MP患者56例纳入本次研究,将其记为观察组,给予常规治疗后,有效者49例,无效者7例。另选同期在我院进行健康体检的志愿者55例作为对照组,对比两组血清SP-A、SP-D及hs-CRP的变化趋势,比较观察组不同治疗结果患者的血清SP-A、SP-D及hs-CRP水平,并分析患者的血清SP-A、SP-D与hs-CRP的相关性。结果:治疗后3d及治疗后7d观察组的血清SP-A、SP-D及hs-CRP水平较治疗前依次降低,但均高于对照组(P0.05),在治疗后14d血清SP-A、SP-D及hs-CRP水平较治疗前降低(P0.05),但与对照组比较差异无统计学意义(P0.05)。治疗后14 d有效组血清SP-A、SP-D及hs-CRP水平均明显低于无效组,差异有统计学意义(P0.05)。根据Spearman相关性分析结果显示,MP患者的血清SP-A、SP-D与hs-CRP均呈正相关(r=0.713、0.699,P=0.000、0.000)。结论:MP患者的血清SP-A、SP-D及hs-CRP水平可伴随治疗过程的进行而逐渐回落,最终基本恢复至正常范围,且血清SP-A、SP-D水平与hs-CRP水平呈正相关,临床治疗时可针对上述3种指标进行监测以判断患者病情及治疗效果。     

Pulmonary collectins modulate strain-specific influenza a virus infection and host responses

Collectins are secreted collagen-like lectins that bind, agglutinate, and neutralize influenza A virus (IAV) in vitro. Surfactant proteins A and D (SP-A and SP-D) are collectins expressed in the airway and alveolar epithelium and could have a role in the regulation of IAV infection in vivo. Previous studies have shown that binding of SP-D to IAV is dependent on the glycosylation of specific sites on the HA1 domain of hemagglutinin on the surface of IAV, while the binding of SP-A to the HA1 domain is dependent on the glycosylation of the carbohydrate recognition domain of SP-A. Here, using SP-A and SP-D gene-targeted mice on a common C57BL6 background, we report that viral replication and the host response as measured by weight loss, neutrophil influx into the lung, and local cytokine release are regulated by SP-D but not SP-A when the IAV is glycosylated at a specific site (N165) on the HA1 domain. SP-D does not protect against IAV infection with a strain lacking glycosylation at N165. With the exception of a small difference on day 2 after infection with X-79, we did not find any significant difference in viral load in SP-A(-/-) mice with either IAV strain, although small differences in the cytokine responses to IAV were detected in SP-A(-/-) mice. Mice deficient in both SP-A and SP-D responded to IAV similarly to mice deficient in SP-D alone. Since most strains of IAV currently circulating are glycosylated at N165, SP-D may play a role in protection from IAV infection.