DESCRIPTION

CHI3L1 (YKL-40) is a secreted glycoprotein of the glycoside hydrolase family 18 that lacks chitinase activity but binds chitin, heparin, and hyaluronan. It is produced mainly by macrophages, neutrophils, chondrocytes, synovial cells, epithelial cells, and glial cells, with expression induced by inflammatory cytokines such as IFN-γ and IL-6. Functionally, CHI3L1 is a pleiotropic mediator that regulates cell proliferation, adhesion, migration, and activation; induces inflammatory mediators (CCL2, CXCL2, MMP-9); inhibits apoptosis; promotes Th2 responses and angiogenesis; and chemoattracts endothelial cells, thereby driving tissue remodeling, inflammation, and tumor progression. Clinically, elevated circulating CHI3L1/YKL-40 correlates with poor prognosis in multiple cancers, neurodegenerative diseases, and inflammatory/metabolic conditions.

PRINCIPLE OF THE ASSAY

An anti-tag antibody is pre-coated onto the bottom of wells. After adding antigen or samples, Tagged-Capture antibody and HRP-conjugated detection antibody, a sandwich complex is formed in the solution. TMB acts as a HRP substrate, and the solution color will change from colorless to blue. A stop solution containing sulfuric acid turns the solution yellow. The color intensity is proportional to the quantity of bound protein, which is measurable at 450 nm with the correction wavelength set at 630 nm.

PRECISION

Intra-assay Precision (Precision within an assay) Three samples of known concentration were tested 8 times on one plate to assess intra-assay precision. Inter-assay Precision (Precision between assays) Three samples of known concentration were tested in 16 separate assays to assess inter-assay precision.

Intra-assay Precision

Sample	n	Mean (pg/mL)	SD	CV%
1	8	1,013.1	37.6	3.7
2	8	266.8	9.7	3.6
3	8	152.6	8.1	5.3

Inter-assay Precision

Sample	n	Mean (pg/mL)	SD	CV%
1	16	1014.2	33.4	3.3
2	16	265.9	9.9	3.7
3	16	151.4	6.1	4.0

RECOVERY

The recovery of human CHI3L1/YKL40 spiked to three different levels throughout the range of the assay in various matrices was evaluated.

Sample Type		Average% of Expected	Range (%)
Human serum	1:160	107	104-109
	1:320	110	106-115
Cell culture supernatant	1:640	101	88-108
	1:1,280	103	101-107
Urine	1:4	95	91-102
	1:8	82	73-91
CSF	1:6,400	104	100-108
	1:12,800	109	106-113

LINEARITY

To assess the linearity of the assay, samples were diluted with the appropriate Sample Diluent to produce samples with values within the dynamic range of the assay. (The human serum and cell culture supernatant was initially diluted 1:80. The urine was initially diluted 1:2. The CSF was initially diluted 1:800.)

		Human serum	Cell culturesupernatant	Urine	CSF
1:2	Average% of Expected	100	100	100	100
	Range (%)	-	-	-	-
1:4	Average% of Expected	100	105	110	112
	Range (%)	97-103	97-112	102-119	100-124
1:8	Average% of Expected	105	106	108	106
	Range (%)	102-109	99-112	104-112	97-115
1:16	Average% of Expected	99	109	108	107
	Range (%)	96-101	101-117	101-115	94-121

CALIBRATION

This immunoassay is calibrated against a highly purified recombinant human Human CHI3L1/YKL40 One-Step ELISA Kit produced at Sunlong Medical™.