DESCRIPTION

TNFSF13B, also named as BAFF, BLYS, TALL1, TNFSF20, ZTNF4 and CD257, is a cytokine that binds to TNFRSF13B/TACI and TNFRSF17/BCMA. TNFSF13B is localized in chromosome region 13q32-q34 and is implicated in the regulation of immune response to infections, autoimmune disease, and inflammation. BAFF is a critical cytokine supporting the survival of naive B cells, acting through the BAFFR receptor. At the placental level, it is believed that TNFSF13B has an antiapoptotic effect. TNFSF13B is overexpressed in several autoimmune patients although the mechanism behind this feature is unclear.

PRINCIPLE OF THE ASSAY

Sandwich ELISA structure (Detection antibody labeled with HRP) A capture antibody is pre-coated onto the bottom of wells which binds to analyte of interest. A detection antibody labeled with HRP also binds to the analyte. TMB acts as the HRP substrate and the solution color will change from colorless to blue. A stop solution containing sulfuric acid turns 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	4,317.4	193.4	4.5
2	8	1,028.0	44.4	4.3
3	8	544.8	30.8	5.7

Inter-assay Precision

Sample	n	Mean (pg/mL)	SD	CV%
1	16	4,243.5	179.0	4.2
2	16	1,033.5	49.0	4.7
3	16	549.4	32.0	5.8

RECOVERY

The recovery of mouse BAFF spiked to three different levels throughout the range of the assay in various matrices was evaluated.

Sample Type		Average% of Expected	Range (%)
Mouse serum	1:16	97	90-104
Cell culture supernatant	1:2	92	87-96

LINEARITY

To assess the linearity of the assay, cell culture supernatant samples were spiked with high concentrations of mouse BAFF and diluted with the appropriate Sample Diluent to produce samples with values within the dynamic range of the assay. Mouse serum samples were diluted with the appropriate Sample Diluent to produce samples with values within the dynamic range of the assay. (The mouse serum was initially diluted 1:2.)

		Cell culture supernatant	Mouse serum
1:2	Average% of Expected	89	100
	Range (%)	85-93	-
1:4	Average% of Expected	85	105
	Range (%)	82-89	104-107
1:8	Average% of Expected	91	104
	Range (%)	89-92	96-110
1:16	Average% of Expected	92	105
	Range (%)	86-98	98-113

CALIBRATION

This immunoassay is calibrated against a highly purified recombinant mouse BAFF produced at Sunlong Medical™.