Modulation of purinergic signalling in macrophages and T cells by Trichinella spiralis secreted proteins

Abstract

Extracellular nucleotides are signalling molecules whose purinergic receptor-mediated effects are known to be key regulators of inflammatory and other immune responses, and they are considered archetypal activators of the innate immune system. It has been shown by our group that infective larvae of Trichinella spiralis secrete enzymes which catalyze the degradation of extracellular nucleotides, and thus potentially interfere with host cell purinergic receptor signalling. Murine bone marrow-derived macrophages (BMMΦ) of various activation states and CD4+ T cells were used to examine the effects of T. spiralis secreted proteins on immune cell purinergic signalling. This study showed, by PCR and pharmacological analyses, that these cell types possess functional purinergic receptors and the sub-types of receptors responsible for the signalling events were identified. It was shown that the ecto-nucleotidases, CD39 and CD73, were functionally expressed on BMMΦ and CD4+ T cells. The signalling events which were triggered following purinergic receptor stimulation were inhibited by T.spiralis secreted enzymes due to metabolism of nucleotides to adenosine. It was shown that the action of T.spiralis secreted proteins enhanced anti-inflammatory processes, such as IL-10 release and arginase I activity in BMMΦ, while NO, TNF-α and IL-6 release were inhibited. In CD4+ T cells, proliferation and cytokine release were all inhibited by adenosine generation. Pharmacological characterisation of adenosine-induced effects on these cells showed that they were predominantly due to A2R activation. In addition to the interference with purinergic signalling, T.spiralis secreted products were shown to have direct effects on BMMΦ and T cell effector functions and this was shown to be due to the glycan component of the secreted proteins. In BMMΦ, T.spiralis glycans appeared to activate C-type lectins, and in particular, the Macrophage Galactose Lectin (MGL). Thus the parasite, via its secreted proteins, appears to interfere with host purinergic signalling as well as having direct effects on immune cells by activation of C-type lectins.