Table 1.

Detection of unmasked forms of CD22 on transfected COS cells and lymphoid cell suspensions

Cell population	% Of cells positive for CD22	% Of cells positive for α2,6-PAA	% Of cells positive for α2,3-PAA
CD22-transfected COS cells	20·0 ± 6·2	21·0 ± 6·4	2·6 ± 0·7
Sham-transfected COS cells	0·9 ± 0·1	1·4 ± 0·1	1·0 ± 0·2
Bone marrow	4·7 ± 1·8	0·9 ± 0·1	0·3 ± 0·2
Lymph node	12·2 ± 2·5	1·0 ± 0·1	0·1 ± 0·1
Spleen	21·0 ± 7·0	1·0 ± 0·1	0·4 ± 0·2

The indicated cell populations were incubated with NeuAcα2,6Galβ1,4Glc coupled to biotinylated polyacrylamide (α2,6-PAA) or NeuAcα2,3Galβ1,4Glc coupled to biotinylated polyacrylamide (α2,3-PAA) and binding revealed with streptavidin-coupled fluorescein isothiocyanate (FITC). Separate samples of cells were stained for surface CD22 expression using anti-CD22 monoclonal antibody (mAb) followed by anti-mouse-FITC antibody. The percentage of cells staining positively for each marker when analysed by fluorescence microscopy is shown. CD22 bound specifically to α2,6-PAA but did not bind α2,3-PAA. In other experiments, COS cells transfected with mouse sialoadhesin cDNA were found to bind specifically to the α2,3-PAA probe (results not shown). Data represent mean values ± SD from four to 18 experiments.