DESCRIPTION

CD22, also known as Siglec-2 (sialic acid binding Ig-like lectin 2) or BL-CAM (B-lymphocyte cell adhesion molecule), is a 130-140 kDa, B-cell restricted, type I transmembrane glycoprotein belonging to the immunoglobulin gene superfamily. The expression of CD22 is developmentally regulated. It is expressed at low levels in the cytoplasm of pro-B and pre-B cells and present on the cell surface only at mature stages of B-cell differentiation. Cell surface expression is lost during terminal differentiation into plasma cell and after B-cell activation. CD22 is an inhibitory receptor for B-cell receptor (BCR) signalling, preferentially binds to alpha-2,6-linked sialic acid and mediates B-cell B-cell interactions. It plays a crucial role in activation and differentiation of the Bcell. Soluble form of CD22 (sCD22) has been found in human serum and may be useful as a tumor marker for hairy cell leukemia.

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 (ng/mL)	SD	CV%
1	8	5.32	0.09	1.69
2	8	1.32	0.02	1.52
3	8	0.66	0.01	1.52

Inter-assay Precision

Sample	n	Mean (ng/mL)	SD	CV%
1	16	5.30	0.07	1.32
2	16	1.32	0.02	1.52
3	16	0.66	0.01	1.52

RECOVERY

The recovery of human CD22 spiked to three different levels throughout the range of the assay in various matrices was evaluated.

Sample Type		Average% of Expected	Range (%)
Human plasma	1:2	87	72-117
Cell lysate	1:256	109	104-117
	1:512	106	103-114

LINEARITY

To assess the linearity of the assay, human plasma samples were spiked with high concentrations of human CD22 and diluted with the appropriate Sample Diluent to produce samples with values within the dynamic range of the assay. Cell lysate 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 1:32.)

		Human plasma	Cell lysate
1:2	Average% of Expected	75	100
	Range (%)	71-78	-
1:4	Average% of Expected	88	100
	Range (%)	87-90	96-102
1:8	Average% of Expected	98	99
	Range (%)	94-102	97-102
1:16	Average% of Expected	104	94
	Range (%)	88-120	91-97

CALIBRATION

This immunoassay is calibrated against a highly purified recombinant human CD22 produced at Sunlong Medical™.