Dendritic cells (DC) are important initiators of an immune response so understanding the factors controlling antigen acquisition and presentation has important consequences for the use of these cells in vaccines and other forms of immunotherapy. We investigated the factors that influence phagocytosis by immature bone marrow‐derived DC (BMDC) and the effect of interleukin‐10 (IL‐10) on this process. Two sizes of fluorescent particles and recombinant bacillus Calmette–Guèrin expressing the green fluorescent protein (rBCG) were used as particulate antigens. The percentage of cells taking up the antigen was found to be dependent on the size and dose of the particles, and the length of exposure to them. BMDC exposed to IL‐10 at various concentrations for different periods exhibited no distinguishable change in antigen uptake. However, if BMDC treated with IL‐10 and rBCG were then exposed to a second dose of particulate antigen, uptake was increased compared with those BMDC not treated with IL‐10. The expression of major histocompatibility complex class II, CD80, CD86 and CD11c by BMDC after phagocytosing rBCG or inert beads, was inhibited when the BMDC were pretreated with IL‐10. In contrast, the expression of CD25 was increased. BMDC that had taken up BCG or purified protein derivative (PPD) were able to stimulate primed T‐cell proliferation but this was severely inhibited if the BMDC were cultured with IL‐10 before exposure to the antigen. This work suggests that although IL‐10 does not affect the phagocytic capacity of BMDC, it does inhibit maturation of the cells and consequently, T‐cell activation
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