SCIN Antibody
Description
Definition and Function of SCIN Antibody
SCIN (Staphylococcal Complement Inhibitor) is a 13-kDa protein secreted by S. aureus to inhibit the complement system, a key component of innate immunity. SCIN binds to the C3 convertase complex, stabilizing it in an inactive form and preventing the deposition of C3b on bacterial surfaces. This suppresses phagocytosis and recruitment of immune cells, facilitating bacterial persistence .
The SCIN Antibody (humAb 6D4) is a human monoclonal antibody that specifically recognizes and inhibits SCIN. It binds to residues 26–36 of SCIN’s N-terminal region, which overlaps with the protein’s active site. This interaction neutralizes SCIN’s complement-inhibitory activity, restoring immune-mediated bacterial clearance .
Discovery and Development
HumAb 6D4 was identified through a random screen of B-cells from individuals exposed to S. aureus. Its specificity for SCIN was confirmed via BLAST analysis, which revealed limited homology to other bacterial proteins . Key developmental milestones include:
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Target Validation: Studies demonstrated that 6D4 inhibits SCIN-mediated complement evasion in vitro and in vivo .
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Serum Stability: The antibody retains binding affinity for SCIN in human serum, enabling its use in diagnostic assays .
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Detection Methods: Fluorescently labeled 6D4 (e.g., 6D4–800CW) allows visualization of SCIN on bacterial surfaces .
Mechanism of Action
SCIN Antibody disrupts S. aureus immune evasion by:
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Blocking SCIN Activity: Prevents SCIN from stabilizing C3 convertases, restoring complement-mediated lysis and phagocytosis .
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Enhancing SCIN Detection: Facilitates identification of SCIN-producing S. aureus strains in clinical isolates, overcoming limitations of PCR-based methods .
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Synergistic Effects: Co-administration with other immunomodulators may enhance bacterial clearance .
4.1. Diagnostics
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Rapid Detection: 6D4–800CW enables one-step identification of SCIN-producing S. aureus in clinical samples .
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Improved Sensitivity: Detects SCIN in 23/24 scn-positive isolates, including strains missed by PCR .
4.2. Therapy
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Complement Activation: Neutralizes SCIN, enhancing innate immune responses against S. aureus .
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Antibiotic Synergy: May reduce reliance on antibiotics by boosting host immunity .
5.1. Prevalence in S. aureus Strains
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SCIN is expressed by 95% of S. aureus isolates, including methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) strains .
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6D4 binds to SCIN in diverse clinical isolates, including USA300 and Newman strains .
5.2. Correlation with SARS-CoV-2 Immunity
Higher SCIN Antibody levels correlate with increased neutralizing antibodies against SARS-CoV-2, suggesting cross-reactive immune responses .
Table 1: Characteristics of SCIN Antibody (humAb 6D4)
Table 2: SCIN Inhibition by 6D4 vs. Native SCIN Activity
| Parameter | Native SCIN Activity | SCIN + 6D4 |
|---|---|---|
| C3b Deposition | Inhibited | Restored |
| Phagocytosis | Reduced | Enhanced |
| Complement Lysis | Suppressed | Activated |
Product Specs
Target Background
- Research suggests that Scinderin (Scin) plays a crucial role in the development of developmental dysplasia of the hip (DDH). PMID: 28213129
- Epistasis analysis revealed a statistically significant interaction between CDC42 and SCIN SNPs, which are strongly associated with CDC42 and SCIN gene expression levels and map to regulatory elements in skin cells. This interaction has important biological relevance since CDC42 and SCIN proteins have opposing effects on actin cytoskeleton organization and dynamics, underlying melanoma cell migration and invasion. PMID: 27347659
- High levels of SCIN expression in gastric cancer tissue correlate with poor prognosis for patients. SCIN enhances the invasion and metastasis of GC cells through activating the Cdc42 pathway to increase the formation of filopodia. PMID: 27033455
- Suppression of Scinderin impairs the proliferation and migration of gastric cancer SGC7901 cells and attenuates its epithelial-mesenchymal transition process. PMID: 25174406
- SCIN plays a significant role in lung carcinoma cell proliferation. PMID: 25303873
- These findings suggest that SCIN plays a critical role in the proliferation of prostate cancer cells and lentivirus-mediated inhibition of SCIN expression may be a potential therapeutic approach for the treatment of prostate cancer. PMID: 24212916
- Scinderin expression does not correlate with prognosis in head and neck cancer. PMID: 24330498
- Calcium binding to the N terminus of Adseverin dominates the activation process to expose the F-actin binding site on A2. PMID: 19666531
Q&A
Q1: What are the primary experimental applications of SCIN antibodies in microbial research?
SCIN antibodies are primarily used for detecting and inhibiting the staphylococcal complement inhibitor (SCIN) protein, a key virulence factor in Staphylococcus aureus. Applications include:
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Pathogen detection: Human monoclonal antibodies (e.g., 6D4) enable near-infrared fluorescence imaging to identify SCIN-producing S. aureus strains .
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Complement inhibition assays: 6D4 binds residues 26–36 of SCIN’s N-terminus, blocking its interaction with C3 convertases and preventing complement-mediated lysis .
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Serological profiling: SCIN antibodies are used to analyze cross-reactivity with other microbial antigens, such as in COVID-19 studies linking SCIN IgG levels to SARS-CoV-2 neutralizing antibodies .
Methodological Note: For pathogen detection, validate antibody specificity using Western blotting with purified SCIN and negative controls (e.g., scn-negative S. aureus isolates) .
Q2: What distinguishes monoclonal vs. polyclonal SCIN antibodies in research?
Example: Monoclonal 6D4 is preferred for studying SCIN’s complement inhibition mechanism, while polyclonals (e.g., Abcam ab223055) are suited for cytoskeletal studies in human/mouse cells .
Q3: How should I design experiments to resolve discrepancies in SCIN antibody detection across studies?
Discrepancies often arise from differences in:
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Antigen preparation: SCIN’s Ca²⁺-dependent conformation affects antibody binding. Use calcium-free buffers to stabilize the protein for epitope exposure .
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Species reactivity: SCIN antibodies may cross-react with homologs in non-human pathogens. For S. aureus studies, confirm scn gene presence via PCR alongside antibody detection .
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Sample treatment: Human serum incubation enhances SCIN binding to S. aureus through C3b deposition. Normalize serum exposure times to standardize detection .
Validation Protocol:
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Negative controls: Use scn-negative S. aureus strains or SCIN knockout cells.
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Positive controls: Purified recombinant SCIN (e.g., Nordic Biosite KIAA1905) .
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Quantification: Use multiplex assays (e.g., Luminex) to measure SCIN alongside other complement inhibitors .
Q4: What strategies optimize SCIN antibody performance in immunohistochemistry (IHC)?
Optimal IHC protocols for SCIN detection include:
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Antigen retrieval: Heat-induced epitope retrieval (HIER) with citrate buffer (pH 6.0) to unmask SCIN in formalin-fixed tissues .
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Blocking: Use 5% non-fat milk or BSA to reduce non-specific binding.
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Primary antibody dilution:
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Detection systems: HRP or fluorescent tags (e.g., Alexa Fluor 488) for single/multiplex staining .
Troubleshooting:
| Issue | Solution |
|---|---|
| Low signal | Increase primary antibody incubation time |
| Non-specific staining | Optimize blocking reagents |
| Cross-reactivity | Use epitope-specific monoclonals (e.g., 6D4) |
Q5: How do SCIN antibodies contribute to multi-omics studies, such as in COVID-19 research?
SCIN antibodies are part of microbial antigen microarrays used to profile IgG responses. In COVID-19 vaccine studies:
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Neutralizing antibody correlation: High SCIN IgG levels correlate with elevated SARS-CoV-2 neutralizing antibodies, suggesting shared immune mechanisms .
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Pathogen interaction analysis: SCIN antibodies help identify microbial antigens that modulate vaccine responses, aiding in adjuvant or therapeutic development .
Methodology:
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Microarray design: Include SCIN alongside other bacterial/viral antigens (e.g., influenza, rubella).
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Data analysis: Use SHAP (SHapley Additive exPlanations) values to rank antigens by their impact on neutralizing antibody titers .
Q6: What are emerging applications of SCIN antibodies beyond infectious disease research?
SCIN antibodies are being explored in:
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Cytoskeletal dynamics: Polyclonal antibodies (e.g., Abcam ab223055) study SCIN’s role in actin severing and exocytosis in megakaryocytes and osteoclasts .
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Cancer biology: SCIN’s inhibition of cell proliferation and tumorigenesis suggests potential applications in oncology .
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Biomarker discovery: SCIN antibodies may identify dysregulated cytoskeletal proteins in chronic inflammatory diseases .
Future Directions:
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Single-cell analysis: Combine SCIN antibodies with scRNA-seq to map cytoskeletal protein expression in heterogenous cell populations.
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Therapeutic targeting: Develop SCIN-neutralizing antibodies to block its complement-inhibiting activity in S. aureus infections .
Q7: How should I interpret conflicting data on SCIN antibody specificity across species?
Conflicts often stem from:
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Homology differences: SCIN shares ~60% sequence identity between S. aureus and human SCIN (adseverin). Polyclonals may cross-react with conserved regions .
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Post-translational modifications: Phosphorylation or glycosylation can alter epitope accessibility. Use protease-treated lysates to confirm linear epitope binding .
Resolution Steps:
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Sequence alignment: Compare target regions (e.g., N-terminus residues 26–36 for S. aureus SCIN) to predict cross-reactivity.
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Species-specific validation: Test antibodies on SCIN knockouts or homologous proteins (e.g., human adseverin) .
Q8: What novel techniques integrate SCIN antibodies into cutting-edge research?
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Single-molecule localization microscopy (SMLM): Near-infrared-labeled 6D4 enables super-resolution imaging of SCIN on S. aureus surfaces .
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CRISPR-screening: Combine SCIN antibodies with CRISPR knockouts to study gene-protein interactions in bacterial pathogenesis.
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Synthetic biology: Engineer SCIN-binding antibodies for biosensor applications in real-time infection monitoring.
Case Study: 6D4–800CW-labeled antibodies enabled one-step detection of SCIN-producing S. aureus in clinical isolates, bypassing PCR .
