C1QB: Complement C1q B Chain
Key Initiator of the Classical Complement Pathway and Immune Homeostasis
Gene Information Card
| Symbol | C1QB |
|---|---|
| Full Name | Complement C1q B Chain |
| Gene Type | Protein coding |
| Chromosomal Location | 1p36.12 |
| NCBI Gene ID | 713 ncbi.nlm.nih.gov/gene/713 |
| Ensembl ID | ENSG00000173369 |
| UniProt ID | P02746 |
| OMIM ID | 120570 |
| HGNC ID | 1242 |
| Aliases | C1QG, C1QB_HUMAN |
Description
C1QB encodes the B-chain polypeptide of complement C1q, a 460-kDa heterotrimeric protein complex composed of 6 A-chains, 6 B-chains, and 6 C-chains. C1q is the first subcomponent of the classical complement pathway and plays a critical role in immune surveillance by recognizing immune complexes, apoptotic cells, and pathogens. The B-chain contains a collagen-like region and a globular head domain responsible for target recognition. C1q deficiency due to C1QB mutations is strongly associated with systemic lupus erythematosus (SLE) and other autoimmune disorders.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Systemic Lupus Erythematosus (SLE) | Loss of C1q function impairs clearance of apoptotic debris and immune complexes, leading to autoantibody production and tissue inflammation. | OMIM #120570; NCBI GeneReviews |
| Hypocomplementemic Urticarial Vasculitis (HUVS) | C1q deficiency or dysfunction results in immune complex deposition and complement consumption, causing urticarial lesions and vasculitis. | OMIM #120570; ClinVar |
| C1q Deficiency (Immunodeficiency) | Homozygous or compound heterozygous mutations in C1QB abolish C1q activity, predisposing to recurrent infections and autoimmune disease. | OMIM #613652; NCBI GeneReviews |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Liver | 12.5 | Medium |
| Spleen | 8.3 | Medium |
| Lung | 6.1 | Low |
| Kidney | 4.7 | Low |
| Heart | 2.9 | Low |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| HepG2 (liver) | 15.2 | Hepatocyte line; high C1q production |
| THP-1 (monocyte) | 9.8 | Macrophage-like; induced by differentiation |
| A549 (lung) | 5.4 | Epithelial line; moderate expression |
| K562 (leukemia) | 1.2 | Low expression; myeloid origin |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| c.154C>T (p.Arg52*) | Nonsense | Rare | Premature stop; loss of B-chain; C1q deficiency |
| c.286G>A (p.Gly96Arg) | Missense | Rare | Disrupts collagen triple helix; impaired secretion |
| c.487C>T (p.Arg163Trp) | Missense | Rare | Alters globular head; reduced target binding |
Mutation functional classification
Loss of Function (LOF)
Most C1QB mutations are loss-of-function, leading to complete C1q deficiency or severely reduced C1q activity, impairing immune complex clearance and predisposing to SLE.
Gain of Function (GOF)
No gain-of-function mutations reported for C1QB.
Dominant Negative (DN)
Heterozygous missense mutations (e.g., p.Gly96Arg) may exert dominant-negative effects by disrupting multimer assembly, though most cases require biallelic loss.
View complete mutation data：
Gene Ontology (GO)
Pathways
• Complement cascade (classical pathway) – Reactome R-HSA-166663
• Immune system – Reactome R-HSA-168256
• Scavenging of heme from plasma – Reactome R-HSA-2168880
Protein Summary
Complement C1q B chain (UniProt P02746) is a 253-amino-acid protein that forms a homotrimeric collagen-like triple helix with A and C chains. The N-terminal collagen-like region mediates hexamer assembly, while the C-terminal globular domain (gC1q) recognizes IgG, IgM, pentraxins, and apoptotic cell surfaces. C1q binding triggers C1r/C1s activation and classical pathway initiation. The protein is primarily synthesized in macrophages, dendritic cells, and hepatocytes.
Related Services
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| C1QB Knockout HEK293 Cell Line | EDJ-KQ4155 | Human | 713 | Details Get a Quote |
| C1QB Knockout HeLa Cell Line | EDJ-KQ52741 | Human | 713 | Details Get a Quote |
| C1QB Knockout A-549 Cell Line | EDJ-KQ61213 | Human | 713 | Details Get a Quote |
| C1QB Knockout HCT 116 Cell Line | EDJ-KQ69705 | Human | 713 | Details Get a Quote |
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