Increased susceptibility of periodate-treated tumour cells to human but not to mouse or rat natural killer cells

Identification and characterization of a novel siglec, siglec-7, expressed by human natural killer cells and monocytes

We describe the characterization of sialic acid-binding Ig-like lectin-7 (siglec-7), a novel member of the siglec subgroup of the immunoglobulin superfamily. A full-length cDNA encoding siglec-7 was isolated from a human primary dendritic cell cDNA library. Siglec-7 is predicted to contain three extracellular immunoglobulin-like domains that comprise an N-terminal V-set domain and two C2-set domains, a transmembrane region and a cytoplasmic tail containing two tyrosine residues embodied in immunoreceptor tyrosine-based inhibition motif-like motifs. Overall, siglec-7 exhibited a high degree of sequence similarity to genes encoding CD33 (siglec-3), siglec-5, OBBP1/siglec-6, and OBBP-like protein and mapped to the same region on chromosome 19q13.3. When siglec-7 was expressed on COS or Chinese hamster ovary cells, it was able to mediate high levels of sialic acid-dependent binding to human erythrocytes and soluble sialoglycoconjugates, suggesting that it may be involved in cell-cell interactions. Among human peripheral blood leukocytes, siglec-7 was found to be present at low levels on granulocytes, intermediate levels on monocytes, and relatively high levels on a major subset of natural killer cells and a minor subset of CD8(+) T cells. Immunoprecipitation experiments indicated that siglec-7 is expressed as a monomer of approximately 65 kDa.

Target cell membrane modification and susceptibility to lymphokine activated killer cell mediated lysis. I. Trinitrophenyl has no effect on murine normal cells and tumors

Lymphokine activated killer (LAK) cells selectively recognize and lyse a wide variety of tumor cells, including syngeneic, allogeneic, and xenogeneic cells, by a mechanism which remains unknown. It has been shown that trinitrophenyl modification of human peripheral blood lymphocytes (PBLs) and murine blasts induces sensitivity to lysis by LAK cells. We undertook these studies to examine the effects of trinitrophenyl (TNP) on murine normal cells and tumors. Fresh murine PBLs are resistant to LAK mediated lysis and TNP modification of the cell surface has no effect, in direct contrast to results with human cells. However, the addition of anti-TNP antibody demonstrated lysis of the TNP modified cells by an antibody dependent cellular toxicity mechanism showing that these cells can be lysed by LAK cells. Furthermore, TNP did not induce sensitivity to LAK cell mediated lysis on other normal murine tissues including kidney and bone marrow. The lysis of YAC tumor cells is not inhibited by the addition of TNP modified PBLs. A single cell assay demonstrated no conjugation of LAK effector cells and TNP modified PBLs. LAK cells derived from murine PBLs, as is done in the human, were unable to lyse the TNP modified PBLs, ruling out the origin of the LAK cells as the reason for the different results in humans and mice. These observations represent a difference in the spectrum of target cells lysed by human and murine LAK cells, and also demonstrate a response to TNP modification by fresh murine normal tissues and tumors that differs from that observed with murine blasts.(ABSTRACT TRUNCATED AT 250 WORDS)