Splenic MRC1+cells were replenished by monocytes and showed distinct phenotypic changes in chickens with LPS-induced inflammation. A–G PBMCs were isolated from 3-week-old chickens, labelled with CTV, and transferred into age-matched recipient chickens via the intravenous route (200 μL of 1 × 107 cells). To cause LPS-induced inflammation, recipient chickens were intraperitoneally administered 200 μL of LPS (1 mg/kg body weight) or the same volume of PBS (control) immediately after the cell transfer. At 1, 6, and 48 h after LPS administration, spleens were isolated from recipient chickens, and the splenocytes were stained with anti-chicken MRC1 and MHCII antibodies. Injected PBMCs were distinguished from recipient cells (grey dots) by analysing the CTV+-pre-gated cells (pink dots). In addition, the MRC1+ cells were gated, and the expression of MRC1 and MHCII was examined by flow cytometry for MRC1loMHCIIhi (solid line) and MRC1hiMHCIIlo cells (dashed line). Representative dot plot of the results from 1-, 6-, and 48-h post-adoptive transfer A–F showed the proportion of donor MRC1+ cells (pink) within the recipient MRC1+ populations (grey) in the spleen. The bar graph G represents the proportion of MRC1loMHCIIhi and MRC1hiMHCIIlo cells within CTV+MRC1+ donor cells in the recipient after adoptive transfer (n = 10). H MRC1loMHCIIhi cells were sorted from the spleen of 3-week-old chickens and labelled with CTV. CTV-labelled MRC1loMHCIIhi cells were transferred into age-matched recipient chickens via the intravenous route (200 μL of 1 × 107 cells). Then, the recipient chickens were intraperitoneally administered 200 μL of LPS (1 mg/kg body weight). Pink dots represent donor cells, and grey dots recipient cells. The bar graph displays the proportions of MRC1loMHCIIhi and MRC1hiMHCIIlo cells within CTV+MRC1+ cells (pink in the left panel) at 6 h after the cell transfer (n = 6). Data are represented as the mean values ± SD. * P < 0.05, *** P < 0.001.