Two distinct populations of MRC1+cells were found in spleen from chickens based on the expression of MRC1 and MHCII. Various organs were harvested from 3-week-old chickens. Single cells were stained with anti-chicken MRC1 and MHCII antibodies and analysed by flow cytometry. The gating strategy is shown in Additional file 1. A Representative dot plots of MRC1+ cells in bone marrow, the bursa of Fabricius, thymus, blood, caecal tonsil, and lung (n = 10). An identical gating strategy for MRC1loMHCIIhi and MRC1hiMHCIIlo cells in the spleen was used in each panel. A representative figure from three independent experiments with similar results is shown. B Two distinct populations of spleicn MRC1+ cells are shown. The gate with the solid line represents MRC1loMHCIIhi cells, and the gate with the dashed line represents MRC1hiMHCIIlo cells. C Proportion and D absolute number of MRC1loMHCIIhi and MRC1hiMHCIIlo cells in the spleen. E Single cells prepared from the spleen were stained with anti-chicken MRC1, MHCII, MHCI, and CD80 antibodies. Representative histograms display the surface expression of MRC1, MHCI, MHCII or CD80 on MRC1loMHCIIhi and MRC1hiMHCIIlo cell (upper panel). Dashed histograms represent the isotype control. The bar graph represents the mean fluorescence intensity (MFI) of the target molecules (lower panel). Representative histograms are shown with data from three independent experiments with similar results. Data are represented as the mean ± SD. ***P < 0.001.