Maturation of bovine dendritic cells by lipopeptides

The response of DC, and the subsequent stimulation of T cells, is an essential part of the initiation of immune responses following microbial challenge. The response of human DC to bacterial lipopeptides is mediated by toll-like receptor 2, and is characterised by DC maturation and the enhanced capacity to stimulate of T cells. We report here that bovine DC are also induced to mature following lipopeptide stimulation. Exposure of DC to the model lipopeptide Pam₃CSK₄ was associated with increased expression of MHC, costimulatory molecules, and enhanced secretion of IL-12 and TNFα. Lipopeptide-matured DC were superior in their ability to induce T cell activation and IFNγ secretion. In contrast, exposure of MΦ to lipopeptides induced down-regulation of MHC expression and much lower increases in IL-12 secretion. A lipopeptide derived from the sequence of a relevant mycobacterial lipoprotein, MPB83, also influenced bovine DC by stimulating increases in IL-12 and TNFα secretion. These different changes in bovine DC and MΦ may have important implications for immune responses induced following bacterial infection with uptake of microbes by DC resulting in potentiation of their immunostimulatory capacity and uptake by MΦ having a much less marked effect on immune responses.