Comparable patterns of surface protein expression on monocytes found in the airways and periphery. (A) Back-gating of monocyte phenotypic markers in peripheral blood of healthy controls; blue indicates high expression and red low expression. RNAseq, RNA sequencing. (B) Proportions of circulating CMs expressing CD11b in younger adults (n = 7) and older adults (n = 8), CD11c in younger adults (n = 6) and older adults (n = 9), and CD163 in younger adults (n = 7) and older adults (n = 8). (C) Proportions of CMs in the BAL of healthy volunteers expressing CD11b, CD11c, and CD163 in younger adults (n = 5) and older adults (n = 9). Values shown are mean ± SEM. *, P < 0.05; **, P < 0.01, Mann–Whitney U test.