From Cooling Inflammation
In a previous article, I outlined the role of the vagus nerve in responding to infection/damage signals by producing signals that inhibit inflammation. In a recent article (ref. below), the role of the vagus nerve in gut inflammation was examined using real-time biophotonic labeling. Basically that means that a video camera sensitive to infrared can be used to detect infrared dyes produced when NFkB is activated — the camera is able to visualize regions of inflammation in living mice. Using this technique, researchers were able to demonstrate that cutting the vagus nerve produced heightened inflammation in gut treated with an irritant. The vagus nerve appears to stimulate regulatory T cells that lower the activity of inflammatory cells.
Inflammation/NFkB Activation Visualized in Live Mice
The studies were performed in a mouse line constructed to express an infrared fluorescent protein in cells in which the inflammation transcription factor, NFkB, is activated. Mice of this strain were prepared with and without the vagus nerve intact leading to the intestines. The mice were then exposed to sodium dextran sulfate (DSS) to simulate inflammatory bowel disease symptoms.
Cutting the Vagus Nerve Permits Inflammation
Mice with intact vagus nerves exhibited much less inflammation in their gut than those without vagus innervation. The cut vagus experiments demonstrated that the vagus nerve was responsible for suppressing inflammation. Further experiments were performed to determine if the inflammatory and anti-inflammatory reactions could be transferred to other mice by transferring cells from the treated mice.
Regulatory T Cells (CD4+, CD25+) Block Inflammation
Transfer experiments showed that inflammatory T cells (CD4+, CD25-) from cut vagus, DSS mice would cause bowel inflammation in other mice, but that did not happen with the same type of cells from mice with intact vagus nerves. Further tests showed that either cutting the vagus or adding inflammatory T cells from a mouse with a cut vagus, reduced the population of regulatory T cells (CD4+, CD25+) in control mice treated with DSS. So, without the vagus stimulation, the regulatory T cell population declined in the presence of inflammatory signals.
Absence of Regulatory T Cells Can Explain Many Inflammatory Diseases
In many inflammatory diseases, e.g. celiac, Crohn’s disease, rosacea, there appears to be a deficiency of regulatory T cells. In the absence regulatory T cells, signals from vagus nerves will no longer produce anti-inflammatory suppression. In fact the same nerve signals may become inflammatory. This would explain why rosaceans will become inflamed by hot or cold stimulation that would normally lead to anti-inflammatory stimulation of regulatory T cells. Similarly, capsaicin, castor oil and menthol, which normally produce an anti-inflammatory response, produce inflammation in rosaceans.
O’Mahony C, van der Kleij HP, Bienenstock J, Shanahan F, O’Mahony L. 2009. Loss of vagal anti-inflammatory effect – in vivo visualization and adoptive transfer. Am J Physiol Regul Integr Comp Physiol. Aug 12. [Epub ahead of print]