Effect of CCL18 on LTBMCs. LTBMCs (n = 3 per group) were established from human bone marrow cells. Results of 1 of 3 representative experiments are shown. (A) Half the culture medium was harvested from LTBMCs after each feeding, and the number of nonadherent cells was counted and expressed as mean ± SD. (B) Nonadherent cells harvested from LTBMCs were plated at a concentration of 1 × 10⁴ cells/mL in the presence of cytokine cocktail. After 7 days of culture, the number of colonies was counted, recalculated for the total number of nonadherent cells recovered from LTB-MCs, and expressed as mean ± SD of the number of CFCs. (C) Dose response to CCL18. Colony formation of cells harvested from 5-week-old LTBMCs was determined as described in panel B. The minimal dose showing a statistically significant increase in colony formation was 10 nM (Student t test). (D) Adherent layers from LTBMCs were photographed after 3 weeks of culture (Leica 10×/0.22 numerical aperture [NA] objective). Areas of hematopoiesis are evident in the adherent layers of LTBMCs and increased in the presence of CCL18. (E) CCL18 was added directly to methylcellulose cultures of progenitor cells supplemented with lineage-specific cytokines. In the presence of cytokines, CCL18 decreased colony formation; in their absence, it showed no effect on colony formation.