Identification and characterization of the murine homologue of CD22, a B lymphocyte-restricted adhesion molecule

The human B lymphocyte-specific Ag, CD22, is a cell adhesion molecule expressed on the surface during a narrow window of B cell development, coincident with surface IgD. A ligand for CD22 has recently been identified on human T cells as the low molecular mass isoform of the leukocyte common Ag, CD45RO. CD22 has been reported to function in the regulation of both T and B cell activation in vitro. In this study, we report the isolation and expression of a molecular cDNA clone encoding the murine homologue of CD22, mCD22. Within their predicted protein sequences, murine and human sequences overall have 62% identity, which includes 18 of 20 extracellular cysteines and six of six cytoplasmic tyrosines. BHK cells transfected with mCD22 cDNA specifically adhere to resting and activated T lymphocytes and in addition bound activated, but not resting, B cells. Five Th clones were analyzed for their ability to adhere to mCD22; two Th0 clones and one Th1 clone bound CD22+ BHK transfectants, but not all T cell clones bound CD22+ cells: another Th1 clone and a Th2 clone did not. mCD22+ BHK transfectants were also specifically bound by the B cell-specific mAb, NIM-R6, demonstrating that this mAb is specific for murine CD22. Human cell lines expressing the counter-receptors for human CD22 were also examined for adhesion to the murine CD22 homologue; the epitope responsible for B cell adhesion to CD22 is conserved, whereas the T cell epitope binding to CD22 is not. The cDNA and mAb to murine CD22 will be useful for defining the in vivo function of CD22.     

Expression, exon-intron organization, and chromosome mapping of the human sodium iodide symporter

The active iodide uptake of the thyroid gland in humans is mediated by the human sodium iodide symporter (hNIS). In this report, we show that hNIS expression was detected primarily in thyroid tissue, but also in breast, colon, and ovary tissues. Expression of hNIS is greatly reduced in thyroid tumors compared to normal thyroid tissue. Among tumor tissues, hNIS expression appears to be variable, consistent with the variable response to radioiodide treatment observed for thyroid carcinomas. The coding region of hNIS is interrupted by 14 introns, and the nucleotide sequence of each exon-intron junction is reported. Using this information, an alternatively spliced form of hNIS was identified. Finally, the chromosome location of the hNIS gene was mapped to chromosome 19p.