High-sensitivity immunofluorescence for detection of the pro- and anti-inflammatory cytokines gamma interferon and interleukin-10 on the surface of cytokine-secreting cells

We have shown here that antibody-conjugated magneto fluorescent liposomes can detect as few as 50-100 antigen molecules per cell, and can be used to discriminate clearly the stained cells cytometrically and to isolate them by cell sorting. In general, this new technology will allow the detection of surface molecules expressed at very low but functionally relevant numbers, which were formerly undetectable by conventional means. Liposomes will allow the use of a variety of fluorochromes, including unconventional ones. Here, we identified and characterized the expression of surface forms of IFN-γ and IL-10 on activated T cells secreting these cytokines and various cell lines transfected with the cytokine genes. Our data show that surface cytokine expression is independent of the specific cytokine receptors or the coexpression of cell type-specific accessory molecules. The surface forms of IFN-γ and IL-10 may have distinct in vivo functions, for example, increased or prolonged cytokine signaling in T cell/antigen-presenting cell clusters. Independent of their physiological roles, we were able to demonstrate that because of the specificity of surface display, IFN-γ and IL-10 are unique cytometric surface markers for the unambiguous identification and isolation of viable cells according to the expression of these cytokines.