S100A9 induce expansion of MKs. A and B, Effect of S100A9 protein on mouse MK differentiation. BM cells were cultured in the presence of TPO and S100A9 protein added on day 0 (A) or indicated days (B) of culture. Cells were collected on day 5 and number of CD41+ MKs was determined. C, HPC were cultured with or without S100A9 for 48 hours followed by measuring incorporation of 3[H]Thymidine. D, BM cells cultured with TPO in the presence or absence of S100A9 protein were treated with 10 μmol/L TQ added on day 0. Number of MKs was determined on day 5 of cultures. E, Level of S100A8/A9 protein in BM (n = 32) and PB (peripheral blood; n = 16) plasma of patients with multiple myeloma. F, CD34+ cells isolated from BM of patients with multiple myeloma were differentiated toward MKs in the presence or absence of hS100A9 protein. Proportion and number of CD41a+CD42b+ MKs was determined by flow cytometry on day 12 of cultures. UT, untreated (no S100A9 protein added). Individual values, mean, and SEM values are shown. Statistics: two-tailed Student t test (A, C, and F), one-way ANOVA with Tukey multiple comparison test (B and D), and Mann–Whitney test (E).