Recombinant Human SP-D Protein, CF

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R&D Systems Recombinant Proteins and Enzymes
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Recombinant Human SP-D Protein, CF Summary

Product Specifications

>95%, by SDS-PAGE visualized with Silver Staining and quantitative densitometry by Coomassie® Blue Staining.
Endotoxin Level
<0.10 EU per 1 μg of the protein by the LAL method.
Measured by its ability to bind fluorescein-conjugated E. coli Bioparticles. Kuan, S.F. et al. (1992) J. Clin. Invest. 90:97. The ED50 for this effect is 0.5-3 µg/mL.
Mouse myeloma cell line, NS0-derived human SP-D protein
Ala21-Phe375 (Glu22Gly)
Accession #
N-terminal Sequence
Structure / Form
Predicted Molecular Mass
35.4 kDa (monomer)
40-48 kDa, reducing conditions

Product Datasheets

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Carrier Free

What does CF mean?

CF stands for Carrier Free (CF). We typically add Bovine Serum Albumin (BSA) as a carrier protein to our recombinant proteins. Adding a carrier protein enhances protein stability, increases shelf-life, and allows the recombinant protein to be stored at a more dilute concentration. The carrier free version does not contain BSA.

What formulation is right for me?

In general, we advise purchasing the recombinant protein with BSA for use in cell or tissue culture, or as an ELISA standard. In contrast, the carrier free protein is recommended for applications, in which the presence of BSA could interfere.


Formulation Lyophilized from a 0.2 μm filtered solution in PBS.
Reconstitution Reconstitute at 100 μg/mL in sterile PBS.
Shipping The product is shipped at ambient temperature. Upon receipt, store it immediately at the temperature recommended below.
Stability & Storage: Use a manual defrost freezer and avoid repeated freeze-thaw cycles.
  • 12 months from date of receipt, -20 to -70 °C as supplied.
  • 1 month, 2 to 8 °C under sterile conditions after reconstitution.
  • 3 months, -20 to -70 °C under sterile conditions after reconstitution.
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Background: SP-D

SP-D (surfactant protein-D; also PSP-D) is a 43 kDa member of the collectin family of innate immune modulators. It is constitutively secreted by alveolar lining cells and epithelium associated with tubular structures. Its principal components consist of a collagen-like region and a C-terminal carbohydrate recognition domain (CRD), a structure that further places it in a subset of an expanded group of proteins termed defense collagens (1-4). Human SP-D is synthesized as a 375 amino acid (aa) precursor. It contains a 20 aa signal sequence and a 355 aa mature region. The mature molecule is characterized by the presence of a 25 aa N-terminal linking-region, a 177 aa hydroxyproline and hydroxylysine collagen-like domain, a 46 aa coiled-coil segment, and a 106 aa, C-terminal collectin-like C-type lectin domain (CRD) (5, 6). Two additional, potential isoforms exist. One shows a 13 aa N-terminal extension, while the other combines the N-terminal extension with a deletion of aa’s # 206-375. Mature human SP-D shares 75% and 78% aa identity with mouse and pig SP-D, respectively. Monomeric SP-D is unusual (3). The basic form of SP-D is that of a glycosylated, disulfide-linked 150 kDa trimer that generates an alpha -helical coiled-coil structure linked to a “head” of three symmetrical CRDs (4, 7). Each CRD recognizes the hydroxides of one monosaccharide (4). Trimerization allows for the discrimination of monosaccharide patterns specific to microbial pathogens (7). Typically, SP-D forms a higher-order 620 kDa, X-shaped dodecamer through disulfide bonds associated with the N-terminus (8). This allows for even finer discrimination of self vs. nonself carbohydrate patterns, and facilitates binding to complex antigens (8, 9). One polymorphism, a Met11-Thr11 transition in human, apparently precludes the formation of oligomers, potentially affecting the ability of affected individuals to interact with microorganisms (9, 10). Finally, SP-D is known to bind both SIRP alpha and the calreticulin/CD91 complex on macrophages. When the ratio of antigen/pathogen to available CRDs is low, antigen can be bound without occupying all available CRDs. The free CRDs will bind to SIRP alpha, generating a signal that downmodulates the inflammatory response. When virtually all CRDs are occupied by ligand, however, free CRDs are not available for SIRP alpha binding. Instead, the dodecamer is depicted to undergo a structural rearrangement, exposing the N-termini of all four linked trimers. This exposed terminus is known to bind to the calreticulin/CD91 complex, an event that initiates inflammation. Thus, it would appear that SP-D allows for a graded response to environmental challenge. SP-D provides a mechanism for the clearance of small antigenic insults without the need for a damaging inflammatory response (3).

  1. Holmskov, U. et al. (2003) Annu. Rev. Immunol. 21:547.
  2. Kishore, U. et al. (2006) Mol. Immunol. 43:1293.
  3. Hartl, D. and M. Griese (2006) Eur. J. Clin. Invest. 36:423.
  4. Sim, R.B. et al. (2006) Novartis Found Symp. 279:170.
  5. Rust, K. et al. (1991) Arch. Biochem. Biophys. 290:116.
  6. Lu, J. et al. (1992) Biochem. J. 284:795.
  7. Hakansson, K. et al. (1999) Structure 7:225.
  8. Ohya, M. et al. (2006) Biochemistry 45:8657.
  9. Crouch, E.C. et al. (2006) Am. J. Respir. Cell Mol. Biol. 35:84.
  10. Leth-Larsen, R. et al. (2005) J. Immunol. 174:1532.
Long Name
Surfactant Pulmonary Associated Protein D
Entrez Gene IDs
6441 (Human); 20390 (Mouse)
Alternate Names
COLEC7collectin-7; Collectin 7; Collectin-7; Lung surfactant protein D; PSPD; PSP-D; SFTP4; SFTP4pulmonary surfactant-associated protein D; SFTPD; SPD; SP-D; SP-Dpulmonary surfactant apoprotein; surfactant protein D; surfactant, pulmonary-associated protein D; surfactant-associated protein, pulmonary 4

Citations for Recombinant Human SP-D Protein, CF

R&D Systems personnel manually curate a database that contains references using R&D Systems products. The data collected includes not only links to publications in PubMed, but also provides information about sample types, species, and experimental conditions.

6 Citations: Showing 1 - 6
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  1. Proteomic analysis of the host-pathogen interface in experimental cholera
    Authors: A Zoued, H Zhang, T Zhang, RT Giorgio, CJ Kuehl, B Fakoya, B Sit, MK Waldor
    Nature Chemical Biology, 2021;17(11):1199-1208.
    Species: Vibrio cholerae
    Sample Types: Bacteria
    Applications: Bioassay
  2. Association of surfactant protein D with pulmonary metastases from colon cancer
    Authors: Y Tajima, M Tsuruta, H Hasegawa, K Okabayashi, T Ishida, M Yahagi, A Makino, K Koishikawa, S Akimoto, DD Sin, Y Kitagawa
    Oncol Lett, 2020;20(6):322.
    Species: Human
    Sample Types: Whole Cells
    Applications: Bioassay
  3. Fungal melanin stimulates surfactant protein D-mediated opsonization of and host immune response to <em>Aspergillus fumigatus</em> spores
    Authors: S Sze Wah Wo, M Rani, E Dodagatta-, O Ibrahim-Gr, U Kishore, J Bayry, JP Latgé, A Sahu, T Madan, V Aimanianda
    J. Biol. Chem., 2018;0(0):.
    Species: Human
    Sample Types: Recombinant Protein
    Applications: Characterization
  4. Surfactant Protein D Binds to Coxiella burnetii and Results in a Decrease in Interactions with Murine Alveolar Macrophages.
    Authors: Soltysiak K, van Schaik E, Samuel J
    PLoS ONE, 2015;10(9):e0136699.
    Species: Bacteria - Coxiella burnetii
    Sample Types: Whole Cells
    Applications: Bioassay
  5. MMP-9 cleaves SP-D and abrogates its innate immune functions in vitro.
    Authors: Bratcher, Preston, Weathington, Nathanie, Nick, Heidi J, Jackson, Patricia, Snelgrove, Robert J, Gaggar, Amit
    PLoS ONE, 2012;7(7):e41881.
    Species: N/A
    Sample Types: N/A
    Applications: Enzyme Assay Substrate
  6. The interplay of lung surfactant proteins and lipids assimilates the macrophage clearance of nanoparticles.
    Authors: Ruge CA, Schaefer UF, Herrmann J, Kirch J, Canadas O, Echaide M, Perez-Gil J, Casals C, Muller R, Lehr CM
    PLoS ONE, 2012;7(7):e40775.
    Species: Mouse
    Sample Types: Cell Culture Supernates
    Applications: Bioassay


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Recombinant Human SP-D Protein, CF
By komal patel on 07/25/2020
Application: Binding assay/Protein-protein interaction