Production of 1 alpha,25-dihydroxyvitamin D3 by hematopoietic cells.

Perhaps, 1 alpha,25(OH)2D3 plays a role as a co-factor in the communication between lymphocytes and macrophages. A schematic representation of that proposed interaction is shown in Figure 2. (Formula: see text). For example, macrophages encounter bacteria, stimulating these cells to begin chemotaxis, phagocytosis, and killing of the microorganisms. In addition, the cells produce interleukin-1. Both interleukin-1 and bacterial antigens in the context of the Ia antigens of the macrophages activate T lymphocytes. The T lymphocytes begin to synthesize lymphokines which can further activate macrophages. Macrophages stimulated by IFN-gamma eventually synthesize 1 alpha,25(OH)2D3. Activated lymphocyte express receptors for 1 alpha,25(OH)2D3; and their lymphokine production will decrease in the presence of 1 alpha,25(OH)2D3.