Expression and function of sialoadhesin in rat alveolar macrophages

Alveolar macrophages (Am phi) represent an immunologically distinct sub-pop ulation within the reticuloendothelial system. Phagocytosis and possibly an tigen presentation by Am phi are essential components of specific and innat e primary immune defence processes against inhaled material. The m phi-rest ricted sheep erythrocyte receptor sialoadhesin (Sn) is a member of the immu nglobulin superfamily and binds specifically to sialic acid-containing stru ctures such as selectins and was originally identified as the sheep erythro cyte receptor (SER) responsible for sialic acid-dependent binding of native sheep erythrocytes (SE) to resident murine bone marrow macrophages in rese tting assays. Sn expression has been demonstrated on murine and rat m phi i n lymphatic organs and is recognised by the monoclonal antibody (mAb) ED3 i n the rat. In addition, sialic acid-dependent receptor (SAR) activities tha t mediate rosette formation of alveolar, peritoneal, splenic and bone marro w-resident rat m phi with SE pretreated with gangliosides and SER-like acti vities between native SE and trypsinised Am phi, have been described. The b inding activities of both SAR and Sn show similar characteristics suggestin g that these molecules are closely structurally related or identical. To cl arify the relationship between Sn, SAR and SER-like activities, the binding of mAb ED3 to isolated rat Am phi was investigated by flow cytometry and r esetting assays. It is demonstrated that rat Am phi express Sn and evidence is provided that SAR and SER-like activities are mediated by Sn. (C) 2000 Elsevier Science B.V. All rights reserved.