RESUMO
We recently identified a novel human sialic acid binding immunoglobulin-like lectin, Siglec-8, using mRNA from human eosinophils. To search for a mouse Siglec (mSiglec) ortholog of Siglec-8 and other mouse Siglec paralogs, we conducted public database searches with cDNA sequences of human Siglec-5 to -10 and identified two novel mSiglecs. One has significant sequence identity to human Siglec-5 and is a splice variant of mSiglec-F. The other has greatest sequence identity to human Siglec-10 (mSiglec-G). Both mSiglecs have extracellular Ig-like domains and intracellular tyrosine-based motifs. To determine whether these mSiglecs were relevant to mouse eosinophils, RT-PCR and Northern blot analysis were performed. We detected expression of mSiglec-5 (or -F), -10, and -E mRNA in purified mouse eosinophils, but Northern blot data comparing expression in tissues from normal, IL-5 transgenic, and allergen-sensitized and -challenged mice suggest that mSiglec-10 is probably most relevant to mouse eosinophils.
Assuntos
Antígenos CD/genética , Antígenos de Diferenciação de Linfócitos B/genética , Antígenos de Diferenciação Mielomonocítica/química , Eosinófilos/metabolismo , Lectinas/genética , Sequência de Aminoácidos , Animais , Antígenos CD/química , Antígenos de Diferenciação de Linfócitos B/química , Antígenos de Diferenciação Mielomonocítica/genética , DNA Complementar/análise , Bases de Dados de Ácidos Nucleicos , Humanos , Lectinas/química , Camundongos , Dados de Sequência Molecular , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Lectinas Semelhantes a Imunoglobulina de Ligação ao Ácido SiálicoRESUMO
Sialic acid binding immunoglobulin-like lectin 8 (Siglec-8), which exists in 2 isoforms including one possessing cytoplasmic tyrosine motifs, is expressed only on human eosinophils, basophils, and mast cells. Until now, its function was unknown. Here we define a novel function of Siglec-8 on eosinophils. Siglec-8 cross-linking with antibodies rapidly generated caspase-3-like activity and reduced eosinophil viability through induction of apoptosis. The pancaspase inhibitor benzyloxycarbonyl (Cbz)-Val-Ala-Asp-(Ome)-fluoromethyl ketone (zVAD-FMK) completely blocked this response, implicating caspases in Siglec-8 cross-linking-induced apoptosis. Eosinophil survival-promoting cytokines such as interleukin 5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF) failed to block apoptosis and instead enhanced the sensitivity of eosinophils to undergo apoptosis in response to Siglec-8 antibody. Siglec-8 activation may provide a useful therapeutic approach to reduce numbers of eosinophils (and perhaps basophils and mast cells) in disease states where these cells are important.
