SummaryMonocytes constitute 5-10% of total human peripheral blood leucocytes and remain in circulation for several days before replenishing the tissue macrophage populations. Monocytes display heterogeneity in size, granularity and nuclear morphology, and in the expression of cell membrane molecules, such as CD14, CD16, CD32, CD64, major histocompatibility complex class II, CCR2, CCR5, among others. This has led to the suggestion that individual monocyte/macrophage populations have specialized functions within their microenvironments. This study provides evidence for the occurrence of two peripheral blood monocyte subpopulations on the basis of their differential expression of GM1, a sphingolipid found mostly in lipid rafts, a CD14 + GM1 low population and a CD14 + GM1 high population comprising about 97Á5% and 2Á5% of total CD14 + cells, respectively. GM1 expression correlates with functional differences in terms of endocytic activity, susceptibility to mycobacterial infection, and response to lipopolysaccharide (LPS) (modulation of Toll-like receptor-4 expression). CD14 + GM1 low cells proved to be less endocytic and more responsive to LPS, whereas CD14 + GM1 high cells are more endocytic and less responsive to LPS. In addition, during monocyte to macrophage differentiation in vitro, the percentage of CD14 + GM1 high cells increases from about 2Á5% at day 1 to more than 50% at day 7 of culture. These results suggest that GM1 low and GM1 high monocytes in peripheral blood, represent either different stages of maturation or different subsets with specialized activities. The expression of CD16 on GM1 high favours the first possibility and, on the other hand that up-regulation of GM1 expression and probably lipid rafts function is involved in the monocyte to macrophage differentiation process.

The aim of this study was to investigate whether the J774 mouse macrophage cell line could be used as an in vitro model for dengue virus infection (DENV). After 3 days, infection in J774 cells was assessed by detecting dengue virus non-structural protein 1 (NSP-1) production either by dot blot or indirect immunofluorescence assay (IFA) of saponine-permeabilized J774 cells and then confirmed by RT-PCR (171 bp product, corresponding to the DENV-2 core). Based on the presence of NSP-1 in infected but not in non-infected cells by both IFA and dot blot, as well as the amplification of a 171-bp DENV-2-specific RT-PCR product exclusively in the infected cells, the J774 cell line was found to be permissive for dengue virus infection. As far as we know, this is the first report that the J774 mouse macrophage cell line is infected with dengue virus and, thus, that it can be used as an alternative in vitro model for dengue virus infection studies. This finding could help to further elucidate the mechanisms involved in dengue virus infection and pathogenesis.