PAD4 Antibody
Description
Molecular and Functional Characteristics of PAD4
Structure:
-
Encoded by the PADI4 gene on chromosome 1 (1p36.13), PAD4 is a 663-amino acid protein with a molecular weight of ~74 kDa .
-
Requires calcium ions for activation, binding five calcium ions per subunit .
Function:
-
Regulates epigenetic modifications by deiminating histones H3 and H4, counteracting arginine methylation .
-
Expressed in granulocytes, monocytes, neutrophils, and RA synovial tissues .
Prevalence and Diagnostic Utility
-
Prevalence: Detected in 22–45% of RA patients, compared to ≤13% in other autoimmune diseases (e.g., SLE, Sjögren’s syndrome) .
-
Association with Disease Features:
Table 1: Autoantibody Prevalence in RA Patients vs. Relatives
| Autoantibody | RA Patients (n=82) | First-Degree Relatives (n=147) |
|---|---|---|
| Anti-PAD4 | 29.3% | 1.4% |
| Anti-CCP | 84.0% | 27.1% |
| Rheumatoid Factor | 86.5% | 19.1% |
Pathogenic Role
-
Enhancement of Citrullination: A subset of anti-PAD4 antibodies (e.g., anti-PAD3/4 cross-reactive) activate PAD4 by lowering its calcium requirement, amplifying citrullination and autoantigen production .
-
Immune Complex Formation: PAD4 antibodies may stabilize the enzyme or form immune complexes, contributing to chronic inflammation .
Antibody Subtypes and Effects
| Antibody Type | Function | Example Antibodies |
|---|---|---|
| Agonistic | Activate PAD4 at low calcium | hA288, hA362 |
| Inhibitory | Block enzymatic activity | hI281, hI364 |
| Neutral | Bind without functional impact | Not specified |
Treatment Response
-
Early RA: Anti-PAD4-positive patients show greater improvement in DAS28 after treatment () .
-
Established RA: Anti-PAD4 predicts better response to tofacitinib ± methotrexate vs. methotrexate alone () .
Table 2: Clinical Outcomes by Anti-PAD4 Status
| Parameter | Early RA (Anti-PAD4+) | Established RA (Anti-PAD4+) |
|---|---|---|
| Baseline Joint Damage | No association | Significant association |
| DAS28 Improvement | 22–23% greater | Comparable across treatments |
| Radiographic Progression | Not assessed | Reduced with biologics |
Longitudinal Stability
Research and Clinical Applications
Product Specs
Constituents: 50% Glycerol, 0.01M PBS, pH 7.4
Target Background
In conjunction with SG101, PAD4 is essential for programmed cell death (PCD) triggered by NBS-LRR resistance proteins (e.g., RPS4, RPW8.1, and RPW8.2). This PCD is induced in response to the fungal toxin fumonisin B1 (FB1) and avirulent pathogens (e.g., P.syringae pv. tomato strain DC3000 avrRps4 and pv. maculicola, turnip crinkle virus (TCV), and H.arabidopsidis isolates CALA2, EMOY2, EMWA1, and HIND4).
Along with EDS1, PAD4 provides basal resistance against virulent pathogens by restricting their growth (e.g., H.arabidopsidis isolates NOCO2 and EMCO5, E.orontii isolate MGH, and P.syringae pv. tomato strain DC3000 or expressing HopW1-1 (HopPmaA)). PAD4 is critical for the salicylic acid-(SA-) dependent systemic acquired resistance (SAR) response, which involves the expression of multiple defense responses, including the synthesis of the phytoalexin camalexin and the expression of pathogenesis-related genes (e.g., PR1, ALD1, BGL2, and PR5). This response is triggered by pathogens, initiating a signal amplification loop that increases SA levels via EDS5 and SID2. Importantly, PAD4, in conjunction with EDS1, appears to suppress the ethylene/jasmonic acid (ET/JA) defense pathway.
PAD4 may also function in response to abiotic stresses, such as UV-C light and LSD1-dependent acclimatization to light conditions that promote excess excitation energy (EEE). This suggests that PAD4 might transduce redox signals and modulate stomatal conductance. It further regulates the formation of lysigenous aerenchyma in hypocotyls in response to hypoxia, possibly through hydrogen peroxide production. PAD4 modulates leaf senescence in insect-infested tissue and triggers a phloem-based defense mechanism, including antibiosis (e.g., green peach aphid (GPA), M.persicae), to limit phloem sap uptake and insect growth. This provides an EDS1-independent basal resistance to insects. Additionally, PAD4 participates in the regulation of root meristematic zone-targeted growth arrest alongside EDS1 in a VICTR-dependent manner.
- Overexpression of PAD4 in transgenic Brachypodium distachyon enhances resistance to Puccinia brachypodii PMID: 28836326
- Analysis of regulatory mechanisms reveals unexpected patterns for how the jasmonate (JA), ethylene (ET), phytoalexin-deficient 4 (PAD4), and salicylate (SA) signaling sectors control the transcriptional response to flg22. PMID: 28472137
- The combined action of PAD4, Sag101, and EDS1 promotes salicylic acid-mediated defenses to limit Fusarium graminearum infection in Arabidopsis thaliana. PMID: 25915452
- Research indicates that OsPAD4 (NP_001067424)-involved defense signaling against Xanthomonas oryzae pv. oryzae (Xoo) is jasmonic acid-dependent, while AtPAD4 (NP_190811)-involved defense signaling against pathogens is salicylic acid-dependent. PMID: 24617729
- Overexpression of AtPAD4 increases the resistance of soybean to cyst and root-knot nematodes. PMID: 23617694
- saul1 senescence relies on the PAD4-dependent salicylic acid pathway but does not require NPR1 signaling. PMID: 22706448
- These findings highlight distinct molecular activities of PAD4, determining particular aspects of defense against aphids and pathogens. PMID: 22353573
- Only PAD4 is required for SA-dependent induction of HRT. The presence of PAD4 restores the cytoplasmic localization of EDS1. PMID: 22072959
- PAD4 is essential for the ssi2-dependent heightened resistance to green peach aphid. [SSI2] PMID: 20367470
- Data suggest that the vtc1-1 mutant requires functional PAD4, EDS5, and NPR1 for SA biosynthesis and pathogen resistance. PMID: 20121455
- PAD4 is required for the ssi2-dependent heightened resistance to green peach aphid. PMID: 20367470
- PAD4 modulates the activation of senescence in aphid-infested leaves, contributing to basal resistance to aphids. PMID: 16299172
Q&A
Here’s a structured collection of research-focused FAQs on PAD4 antibodies, synthesized from current literature and tailored for academic investigators:
Advanced Research Questions
How should researchers design experiments to investigate epitope spreading in PAD4 antibody development?
-
Key considerations:
How can conflicting data on environmental triggers (e.g., smoking) be resolved?
-
Contradiction: Smoking correlates with severe RA but shows no direct link to PAD4 antibody development (p = 0.04 for reduced smoking in anti-PAD3/4+ vs. PAD4– groups) .
-
Methodological adjustments:
-
Stratify analyses by antibody subtype (PAD4 mono-reactive vs. PAD3/4 cross-reactive).
-
Incorporate multi-omics (e.g., proteomics, transcriptomics) to disentangle gene-environment interactions.
-
What experimental models best recapitulate PAD4-driven autoimmunity?
Methodological Challenges
How can cross-reactivity between PAD isoforms be minimized in assays?
-
Pre-adsorb sera with PAD3 protein to isolate PAD4-specific antibodies .
-
Validate findings using orthogonal methods (e.g., ELISA + immunoprecipitation).
