S100a8 promotes myeloid development of KSL cells. (A) Naive KSL cells from B6 mice were cultured on OP9 cells with KitL, Flt3L, IL-7, and different concentrations of S100a8. Polymyxin B (100 μg/mL) was also added to inhibit any LPS that may be present. (B) Cell-surface TLR4 protein expression in arthritic (KRNxG7) and control KSL cells using clone UT41. Isotype control staining is shown in blue. Diminished cell-surface TLR4 protein was also seen with MTS510 clone. (C) Experimental scheme for in vitro competitive culture of arthritic and control KSL cells in the presence of LPS. (D top panel) FACS plot depicting myeloid generation (red gate) of KSL cells in response to different doses of LPS. KRNxG7 arthritic mice were used. (Bottom panel) FACS analysis to determine myeloid cells derived from arthritic KSL cells (Ly5.2⁺) or control KSL (Ly5.1⁺). (E) Relative contribution of KSL cells to Mac1/Gr1⁺B220⁻CD3⁻TCRβ⁻Ter119⁻ cells after in vitro competitive culture of arthritic KSL cells (serum-injected B6xG7 mice) and control KSL cells (PBS-injected B6xG7 mice); **P < .01, ***P < .001.