DESCRIPTION

SSB protein, short for Sjögren's syndrome SSB/La antigen, also known as La autoantigen or lupus La protein, is an RNA-binding protein widely distributed in eukaryotic cells. It was first discovered as an autoantigen in the serum of patients with Sjögren's syndrome and systemic lupus erythematosus (SLE). Under cellular stress (such as viral infection or ultraviolet radiation), SSB protein expression is upregulated, potentially participating in cell protection mechanisms.

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 (ng/mL)	SD	CV%
1	8	39.51	1.00	2.52
2	8	10.68	0.26	2.44
3	8	5.19	0.44	8.45

Inter-assay Precision

Sample	n	Mean (ng/mL)	SD	CV%
1	16	41.79	3.07	7.36
2	16	10.67	0.53	4.94
3	16	5.09	0.35	6.92

RECOVERY

The recovery of human SSB spiked to three different levels throughout the range of the assay in cell lysate was evaluated.

Sample Type		Average% of Expected	Range (%)
Cell lysate	1:64	108	93-116
	1:128	108	99-115

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 cell lysate was initially diluted 1:8.)

		Cell lysate
1:2	Average% of Expected	100
	Range (%)	-
1:4	Average% of Expected	73
	Range (%)	72-75
1:8	Average% of Expected	77
	Range (%)	76-78
1:16	Average% of Expected	79
	Range (%)	78-90

CALIBRATION

This immunoassay is calibrated against a highly purified recombinant human Human SSB Sandwich ELISA Kit produced at Sunlong Medical™.