United Kingdom (UK) 
In Figure 1 murine bone marrow-derived macrophages (BMDMs) were pre-blocked with rat anti-mouse CD16 & CD32 (clone FCR-4G8) and stained with non-recombinant anti-F4/80 [Cl:A3-1] conjugated to Alexa Fluor® 647 (AF647), all commercially available from competitors. In Figure 2 BMDMs were stained with recombinant anti-F4/80 [Cl:A3-1] or isotype control (anti-fluorescein [4-4-20 (enhanced)] IgG2b (Ab00102-8.1). In Figure 3 BMDMs were stained with Fc Silent™ recombinant anti-F4/80 [Cl:A3-1] (Ab00106-8.4) or isotype control (Fc Silent™ anti-fluorescein [4-4-20 (enhanced)] IgG2b (Ab00102-8.4). These were fluorescently labelled using the secondary antibody, goat IgG anti-rat IgG (H&L-chain) polyclonal antibody directly conjugated to Alexa Fluor® 647(AF647) commercially available from a competitor. Whilst in Figure 2 the highest fluorescence signal is seen with the recombinant anti-F4/80 IgG2 (the isotype of the original hybridoma-derived antibody), the isotype control IgG2b (Ab00102-8.1) shows considerable signal overlap, indicative of binding of the antibody to Fc-receptors. This illustrates the importance of isotype controls in such experiments when using conventional antibody formats particularly when Fc-blocking reagents are incompatible with the system used due to reactivity with the secondary antibody. The Fc silent™ format however overcomes this issue as seen in Figure 3, where the Fc silent™ recombinant anti-F4/80 (Ab00102-8.4) yields a strong and distinct signal, whilst the isotype control (Ab00102-8.4) shows no discernible difference to the background staining from the secondary antibody alone. Therefore, with Fc Silent™ reagents, no Fc-blocking products are required. [Data courtesy of Lewis Taylor.]