The natural ligands of MR-CTLDs include lysosomal hydrolases, tissue plasminogen activator, myeloperoxidase and thyroglobulin [9] and microbial ligands including
BIBF 1120 from Klebsiella, yeast and HIV [10]. The ligands for MR–CR include lutropin and thyrotropin hormones. It has been demonstrated that, through the CR domain, MR binds to sulphated carbohydrates that are expressed by macrophages in the marginal zone of spleen and the subcapsular sinus of lymph nodes. This binding is believed to direct MR-bearing cells, complexed with CTLD ligands, toward germinal centres and provide a novel way to link innate and adaptive immune responses [2] and [11]. MR has also been identified on human lymphatic endothelium and shown to mediate the binding of lymphocytes through L-selectin at sites of lymphocyte entrance and exit within lymph nodes [12]. Dermal microvascular endothelial
cells also express MR where it has an endocytic function [13]. Thus, the MR provides the first example of a dual function receptor with distinct lectin activities associated with different domains.
