The adoptive transfer experiments additionally demonstrated
The adoptive transfer experiments additionally demonstrated the role of cholinergic regulation in the antibody immune response. Injection of LPI-stimulated B lymphocytes significantly up-regulated both the IgM and IgG responses to cytochrome c in the host. Obviously, this effect was due to activation of the total B lymphocytes injected (which produced activating cytokines like IL-6) and the impact of Bregs induced by LPI treatment was negligible. Inhibiting α7 nAChRs by MLA in the course of LPI activation significantly decreased IgM production and completely abolished the subsequent IgG response developed by the host; the effect of PNU282987 was much weaker but in the same direction. Therefore, α7 nAChR activity was critical for the stimulating effect of LPI-treated cells; the effect being prevented by α7 nAChR inhibition or, to a lesser extent, desensitization in the chronic presence of agonist. This data indirectly suggest that in this experimental scheme α7 nAChRs expressed in B lymphocytes function as classical ion channels. Regarding the inhibitory effect of MLA in LPS-stimulated B lymphocytes, MLA could decrease IgM production by LPI-activated B lymphocytes in vivo. However, we did not find any effect of MLA on the IgM to IgG class switch in vitro. Therefore, the absence of IgG response in mice transferred with LPI+MLA-stimulated B lymphocytes may be related to T lymphocyte activation (anergization) that obviously needs further studies.
In conclusion, signaling through B lymphocyte-expressed α7 nAChRs is an important factor in regulating antibody immune response. Along with the neuronal and T lymphocyte derived, it can be affected by endogenous ACh, which negatively regulates B lymphocyte proliferation. Accordingly, blocking α7 nAChRs in the course of activation favors proliferation but prevents IgM production. In addition, B lymphocyte-expressed α7 nAChRs can induce pro-proliferative signaling in ion-independent manner. Regulatory Foxp3+ and B10 Tryptone express α7 nAChRs and need them for being activated. Finally, the adoptive transfer experiments with LPI-stimulated B lymphocytes demonstrate the potential of cholinergic regulation for immunosuppression.
Acknowledgements We are grateful to Dr. Yevgeniy Nikolskiy for providing us with AChE inhibitors, to Dr. Talma Brenner for MOG35-53 peptide and to Dr. Ana Cumano for IL-4 and CD5- and Foxp3-specific antibodies.
Introduction The idea of a neuro-osteogenic network has made major progress based upon the observation of skeletal innervation, neuromediators in bone (osteo-neuromediators) and the modulation of the nervous system to bone cells, skeletal development and bone turnover (Chenu, 2004, Imai and Matsusue, 2002, Serre et al., 1999). Some signaling molecules in the nervous system, such as neuropeptides, noradrenaline, serotonin and glutamate, have been identified in bone, and these signaling molecules can participate in the control of the activity of bone cells through their functional receptors (Chenu, 2004). These studies provide direct evidence for a complex neurotransmitter-mediated signaling network in bone. Cholinergic activity has been recently shown to favor the accrual of bone mass via the modulation on bone cells (Bajayo et al., 2012, Shi et al., 2010), which has become one of the many significant recent advances in the understanding of the regulation of bone remodeling. Acetylcholine (ACh) is present in both prokaryotes and eukaryotes as a classical neurotransmitter and an ancient signaling molecule (Horiuchi et al., 2003, Wessler et al., 1999). ACh is synthesized and secreted in the nervous system as well as in a variety of non-neuronal cells from mammalian species (Fujii and Kawashima, 2001, Grando and Sa, 1997, Ikeda et al., 1994, Wessler et al., 2001). In addition to the ability of ACh to act as a neurotransmitter, ACh can also exert influences on basic cell functions which include proliferation, differentiation, cell–cell contacts, immune functions, trophic functions, secretion and absorption (Tracey, 2007) in an auto- and paracrine manner via the activation of the widely expressed nicotinic and muscarinic acetylcholine receptors (n- and mAChRs) in non-neuronal cells (Resende and Adhikari, 2009). ACh can also play an intermediary role in the interactions of non-neuronal cells with the external environment, hormones, growth factors, cytokines and the neural system (Wessler and Kirkpatrick, 2008). Cholinergic signaling is terminated by acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), which rapidly degrade acetylcholine into choline and acetate (Massoulie, 2000). AChE and BChE have different tissue-specific distribution patterns; however, both enzymes present in non-neuronal cells (Çokuğraş, 2003).