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Blood. 2006 Nov 1;108(9):3168-75. Epub 2006 Jul 6.

The beta-glucan receptor dectin-1 functions together with TLR2 to mediate macrophage activation by mycobacteria.

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Department of Biological Sciences, Center for Tropical Disease Research and Training, University of Notre Dame, 130 Galvin Life Science Center, Notre Dame, IN 46556, USA.


Pattern recognition receptors (PRRs) play an essential role in a macrophage's response to mycobacterial infections. However, how these receptors work in concert to promote this macrophage response remains unclear. In this study, we used bone marrow-derived macrophages isolated from mannose receptor (MR), complement receptor 3 (CR3), MyD88, Toll-like receptor 4 (TLR4), and TLR2 knockout mice to examine the significance of these receptors in mediating a macrophage's response to a mycobacterial infection. We determined that mitogen-activated protein kinase (MAPK) activation and tumor necrosis factor-alpha (TNF-alpha) production in macrophage infected with Mycobacterium avium or M smegmatis is dependent on myeloid differentiation factor 88 (MyD88) and TLR2 but not TLR4, MR, or CR3. Interestingly, the TLR2-mediated production of TNF-alpha by macrophages infected with M smegmatis required the beta-glucan receptor dectin-1. A similar requirement for dectin-1 in TNF-alpha production was observed for macrophages infected with M bovis Bacillus Calmette-Guerin (BCG), M phlei, M avium 2151-rough, and M tuberculosis H37Ra. The limited production of TNF-alpha by virulent M avium 724 and M tuberculosis H37Rv was not dependent on dectin-1. Furthermore, dectin-1 facilitated interleukin-6 (IL-6), RANTES (regulated on activation, normal T expressed and secreted), and granulocyte colony-stimulating factor (G-CSF) production by mycobacteria-infected macrophages. These are the first results to establish a significant role for dectin-1, in cooperation with TLR2, to activate a macrophage's proinflammatory response to a mycobacterial infection.

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