| dc.description | Mast cells are critical effector cells in allergic responses and play a protective role in host defense against bacterial infections. Cellular responses to a variety of pathogens are dependent on a superfamily of pattern recognition receptors known as Toll-like receptors (TLR). We therefore hypothesized that mast cells express a number of TLRs and require their expression for specific cellular responses to certain pathogen products. Murine bone marrow derived mast cells (BMMC) expressed mRNA for TLR2, TLR4 and TLR6 but not TLR5, while human cord blood derived mast cells (CBMC) expressed mRNA for TLR1, TLR2 and TLR6 but not TLR4. Consistent with the profiles of TLR expression murine BMMC but not human CBMC produced significant levels of NFkappaB-regulated cytokines in response to E. coli LPS. Functional TLR4 expression was required for BMMC IL-6 and TNF production in response to LPS since BMMC from wild type but not TLR4-deficient mice (C3H/HeJ and C57Bl/10ScCr) responded to LPS challenge. Both human and murine mast cells responded to the TLR2 activator S. aureus PGN. PGN induced substantial levels of CBMC GM-CSF and IL-1beta production despite also inducing moderate levels of apoptosis as assessed by caspase activation and a dissipation of mitochondrial membrane potential. Two additional TLR2 activators, zymosan and Pam3CSK4 also activated CBMC. To determine if the different TLR2 activators induce distinct profiles of mediators we analyzed CBMC degranulation and LTC 4 generation. PGN and zymosan, which are known to activate a TLR2/TLR6 dimer dependent pathway induced potent levels of LTC4 (12 (p < 0.001) and 23 (p < 0.001) fold increase respectively over media controls, n = 16) but failed to significantly enhance degranulation. In contrast, the synthetic lipopeptide (Pam3CysSerLys4), which is known to activate a TLR1/TLR2 dimer dependent pathway, induced significant levels of CBMC degranulation (3 fold increase over media control p < 0.001, n = 5) without inducing LTC4. These findings have important implications for the mechanism of mast cell responses to pathogens and their products and suggest novel mechanisms for generating selective mast cell mediator responses. | en_US |
