By Dr. Christopher Kent
Previous columns have discussed the bidirectional communication that occurs between the nervous system and the immune system [1,2,3]. A recent review article published in the Journal of Internal Medicine  has taken these findings a giant step further, by suggesting that the immune system may be regarded as the sixth sense.
Blalock notes that, “The nervous and immune systems produce a common set of peptide and nonpeptide neurotransmitters and cytokines that act on a common repertoire of receptors in the two systems…This complete biochemical information between neurons and immune cells allows the immune system to function as a sensory organ.
“A sixth sense, if you will, that completes our ability to be cognizant not only of the universe of things we can see, hear, taste, touch and smell but also the universe of things that we cannot. These would include bacteria, viruses, antigens, tumour cells and other agents that are too small to see or touch, make no noise, have no taste or odour..”
Blalock terms these “noncognitive stimuli,” noting that they would “result in transmission of information to the CNS via the aforementioned shared signal molecules to cause a physiological response that is ultimately beneficial to the host and detrimental to the infectious agent.”
Another immunologist, David  stated: “Lymphocytes and natural killer cells can be viewed as cellsized sensory organs, continuously sampling the internal environment for things that don’t belong there or for cellular stress or aberrations.” Blalock does not confine the discussion to infectious process, but notes, “Convincing evidence for the mind/immune system concept is found in the numerous effects of stress on immune function,” and that “these left little doubt that the mind is capable of influencing the immune system.”
These findings are of great interest to the chiropractor, whose vitalistic premise suggests that health is dependent upon the ability of the body to properly comprehend the internal and external environment, and making appropriate responses to maintain homeostasis. The Palmers used the term “mental impulse” to describe “an abrupt and vivid suggestion, prompting some unpremeditated action or leading to unforeseen knowledge or insight.” 
Palmer’s concept of the mental impulse, as articulated by Stephenson  is that, “The mental impulse is not an energy at all. It is a message. A message is not a material, an energy, or a thing physical in any sense…Mentality makes it and sends it to an object of matter.” The mental impulse is not limited to the electrochemical action potential, but may express itself through matter using a variety of mechanisms, including chemical messengers and receptors, and electromagnetic and other energies.
Blalock notes that the result of contemporary insights into the function of the immune and neuroendocrine systems is that “metaphor has become reality. What was previously viewed as outside the realm of sensory perception, and therefore metaphysical, is now seen as otherwise.”
The wisdom of traditional chiropractic constructs becomes increasingly apparent as our understanding of biological processes unfolds.
4. Blalock JE: “The immune system as the sixth sense.” Journal of Internal Medicine 2005;257:126138.
5. Davis MM: “Panning for Tcell gold.” The Scientist 2004;18:2829.
6. Palmer DD: “Textbook of the Science, Art and Philosophy of Chiropractic.” Portland, OR. Portland Printing House Company, 1910. Pages 85 and 109.
7. Stephenson RW: “Chiropractic Textbook.” Davenport, IA. The Palmer School of Chiropractic, 1948 edition. P. 294.