Abstract
BackgroundThe mannose receptor is the best described member of the type I transmembrane C-type lectins; however much remains unanswered about the biology of the receptor. One difficulty has been the inability to consistently express high levels of a functional full length mannose receptor cDNA in mammalian cells. Another difficulty has been the lack of a human macrophage cell line expressing a fully functional receptor. Commonly used human macrophage cell lines such as U937, THP-1, Mono-Mac and HL60 do not express the mannose receptor. We have developed a macrophage hybridoma cell line (43MR cells) created by fusion of U937 cells with primary human monocyte-derived macrophages, resulting in a non-adherent cell line expressing several properties of primary macrophages. The purpose of this study was to identify and select mannose receptor-expressing cells using fluorescence-activated cell sorting and to characterize the expression and function of the receptor.ResultsIn the current study we show that the mannose receptor found on this novel cell has endocytic characteristics consistent with and similar to the mannose receptor found on the surface of monocyte-derived human macrophages and rat bone marrow-derived macrophages. In addition, we demonstrate that these cells engage and internalize pathogen particles such as S. aureus and C. albicans. We further establish the transfectability of these cells via the introduction of a plasmid expressing influenza A hemagglutinin.ConclusionsThe 43MR cell line represents the first naturally expressed MR-positive cell line derived from a human macrophage background. This cell line provides an important cell model for other researchers for the study of human MR biology and host-pathogen interactions.
Highlights
The mannose receptor is the best described member of the type I transmembrane C-type lectins; much remains unanswered about the biology of the receptor
Cells Macrophages used in this study included rat bone marrow-derived macrophages (RBMM), U937, and the continuous human macrophage hybridoma cell line 43
The results indicated that the mannose receptor (MR) in 43MR cells has an approximate half-life of 32 hours (Figure 3) which is consistent with published data on the RBMM MR [49]
Summary
The mannose receptor is the best described member of the type I transmembrane C-type lectins; much remains unanswered about the biology of the receptor. One difficulty has been the inability to consistently express high levels of a functional full length mannose receptor cDNA in mammalian cells. Another difficulty has been the lack of a human macrophage cell line expressing a fully functional receptor. Several studies have shown that the MR binds and internalizes ligands via receptor-mediated endocytosis [18,19], and participates in phagocytosis of mannosylated particles and pathogens [20,21]. Mannosylated ligands bind to the MR at the cell surface at neutral pH and are brought into the cell, where they dissociate from the receptor in an acidic endosomal compartment [22,23].
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