NSGS, NSGW41, and MISTRG mice differentially support the development of human myeloid cell lineages. (A) Representative flow cytometry analysis and (B) frequency of human myeloid CD33⁺ cell populations in the BM of recipient mice 22 weeks after engraftment, distinguishing granulocytic (CD33⁺SSC^hi, blue gate) and monocytic (CD33^hiSSC^lo, green gate) cells pregated on live 7-AAD^–mTer119^–mCD45^–hCD45⁺ cells. (A) Numbers and (B) bars indicate frequencies among hCD45⁺ cells expressed as mean ± SD (NSGS mice, n = 4; irradiated MISTRG mice, n = 12; NSGW41 mice, n = 9; nonirradiated MISTRG mice: n = 9). (C) Representative flow cytometry analysis and (D) frequency of human myeloid CD33⁺ cell populations in the blood of recipient mice from panel A compared with human healthy donor blood (n = 6). (E) Representative flow cytometry analysis and (F) frequency of blood human neutrophils (CD66b⁺CD16⁺) within the CD33^+/loSSC^hi population shown in the blue gate in panel C. The insets show representative images of sorted human CD33^+/loSSC^hi granulocytic cells stained by Diff-Quik (scale bar: 20 µm). (G) Representative flow cytometry analysis and (H) frequency of human monocyte subsets (CD33^hiSSC^lo, green gate in panel C further gated on CD117^–FcεR1^–CD203c^– cells) in the blood of recipient mice 10 weeks after engraftment, as defined by CD14 and CD16 expression. (I) Representative images of sorted human CD33^hiSSC^lo monocytes of the indicated CD14/CD16 phenotype stained by Diff-Quik (scale bar, 20 µm). (J) Frequency of cytokine-producing monocytes among human blood or MISTRG mouse blood cells measured by intracellular cell staining for tumor necrosis factor α (TNFα) and IL-6 after ex vivo stimulation with lipopolysaccharide (LPS; 100 ng/mL) or R848 (10 µg/mL) for 24 hours. (K) Tissue macrophages in the lungs and livers of recipient mice compared with normal human tissues, as identified by immunohistochemistry for human CD68. Histograms (B,D,F,H,J) represent mean ± SD.