Suppression of CFU-eo formation by bone marrow stromal cells and IL-4

Abstract

Rationale To determine the relative roles of stromal cells and T lymphocytes in regulation of eosinophilopoiesis. Methods Colony forming units-eosinophil cultures (CFU-eo) were established by placing euthymic (+/+) or athymic (nu −/nu −) BALB/c mice bone marrow cells in methylcellulose with IL-5. Bone marrow stromal cells were cultured with or without IL-1 and supernatants collected. CFU-eo were evaluated in the presence of IL-4 or stromal cell supernatants. Stromal cell production of IL-4 was evaluated by intracellular staining and ELISA. Results CFU-eo in euthymic BALB/c mice was decreased by addition of 100 units/ml (p<0.001) and 50 units/ml IL-4 (p<0.001). Addition of stromal cell supernatant from unstimulated cultures did not decrease the number of CFU-eo in bone marrow cultures from euthymic BALB/c mice. However, exposure of stromal cells to IL-1 resulted in release of cytokines that decreased CFU-eo formation (p<0.05). When bone marrow from nude mice was evaluated, stromal cell supernatants from naïve or IL-1 stimulated cultures suppressed CFU-eo formation (p<0.05). In all cultures, addition of anti-IL-4 mab (11B11) abrogated this suppressive effect of stromal cell supernatants on CFU-eo formation (p<0.01). IL-4 protein was detected in bone marrow stromal cells by both intracellular staining and ELISA. Abundance of IL-4 protein was increased by exposure of stromal cells to IL-1. Conclusions CFU-eo colony formation is suppressed by IL-4 in the bone marrow. Stromal cells produce IL-4 and IL-4 production is increased by exposure to IL-1. This regulatory mechanism dampens bone marrow eosinophil production and does not require the presence of T lymphocytes.