Direct stimulatory effects of the TLR2/6 ligand bacterial lipopeptide MALP-2 on neutrophil granulocytes

Abstract

Bacterial lipopeptides represent a group of bacterial compounds able to trigger the functions of cells of the innate immune response. Whereas diacylated lipopeptides are recognized by TLR2/6 dimers, triacylated lipopeptides were shown to act via TLR2/1 dimers. Although several previous studies dealt with the effect of the TLR2/1 ligand Pam(3)CysSK(4) on neutrophil granulocytes (PMN), it is still not clear whether TLR2/6 ligand lipopeptides can directly influence PMN functions. In the present study we used highly purified human neutrophils to investigate the direct effects of the diacylated mycoplasmal macrophage activating lipopeptide-2 (MALP-2) on the function of neutrophil granulocytes. After exposure to 10 ng/ml MALP-2 neutrophils acquired activated cell shape, secreted IL-8 and MIP-1beta and their phagocytic capacity was enhanced. Analysis of cell surface activation markers confirmed the activating effect of MALP-2, the expression of CD62L was downregulated whereas CD11b was upregulated on PMN after exposure to MALP-2. The constitutive apoptosis of PMN was inhibited after exposure to MALP-2. However, MALP-2 exerted only a short-term effect on the apoptosis of resting neutrophils, a longer lasting effect was observed after transendothelial migration. MALP-2 did not directly induce the production of reactive oxygen intermediates but primed PMN for a fMLP-induced oxidative burst. The migration of neutrophils was enhanced after treatment with MALP-2. This was due, however, to a chemokinetic rather than to a chemotactic effect. Pam(3)CysSK(4) also activated PMN, but in comparison to MALP-2, at higher concentrations. These findings suggest that diacylated lipopeptides are important microbial structures recognized by and acting on neutrophil granulocytes.

Dual Role of Toll-Like Receptors in Asthma and Chronic Obstructive Pulmonary Disease

“…Most TLRs are homodimeric; however, TLR2 can form heterodimers with TLR1 and TLR6 upon recognition of different structures of lipopeptides and lipoproteins (Hasan et al, 2005;Revets et al, 2005;Wilde et al, 2007;Ospelt and Gay, 2010). Furthermore, TLR10 forms heterodimers with TLR1 and TLR2 (Hasan et al, 2005;Ospelt and Gay, 2010).…”

A Toll-Like Receptor 2/6 Agonist Reduces Allergic Airway Inflammation in Chronic Respiratory Sensitisation to Timothy Grass Pollen Antigens

“…TLR2 forms heterodimers displaying a certain ligand specificity; diacylated lipopeptides, e.g. macrophage-activatinglipopeptide of 2 kDa (MALP-2) [15], are sensed via TLR2/6 dimers, whereas triacylated lipopeptides, such as Pam 3 cysSK 4 , require TLR2/1 [8]. Clinical and preclinical data imply that Mycoplasma infections, recognised via TLR2, seem to prevent the establishment of allergic asthma [16,17].…”

“…Pathogen-associated molecular patterns on microbes are sensed by the innate immune system through a variety of specific receptors. Among them, Toll-like receptors (TLRs), which are expressed in a variety of both structural [7] and immune cells [8,9,10,11,12], play an important role. With regard to the observed protection of farmers’ children against allergy and asthma, genetic variations in TLR2, but not in TLR4 [13], are believed to be responsible [14].…”

Cellular Microbiology of Mycoplasma canis

“…This showed that M. canis is capable of eliciting either pro-or anti-inflammatory host responses in a strain-dependent fashion, which might influence the network of immune barriers to dissemination and recruitment and modulation of inflammatory cells at secondary sites (65). Interestingly, exposure to killed M. canis cells elicited cytokine secretion as effectively as exposure to live M. canis cells did, suggesting that diacylated membrane lipopeptides are the activating factors (66)(67)(68)(69)(70)(71). The principal pathogenic effect of exposure to individual mycoplasmal lipoproteins characterized to date is transient inflammation (72), marked by local infiltration of granulocytes, macrophages, and lymphocytes; the production of proinflammatory cytokines; and complement activation (73)(74)(75).…”