Sometimes I feel like I’m in a time warp.
Back when I was a grad student in the early ‘90s, immunologists were vigorously expanding upon Tim Mosmann and Bob Coffman’s seminal insight that helper T cells were actually comprised of functionally distinct Th1 and Th2 T helper cells. (Helper T cells are an important type of white blood cell involved in the adaptive immune response. They “help” B cells make antibodies, but are also responsible for cell-mediated immune responses.) Since that initial discovery, over 16,000 journal articles about Th1 and Th2 cells have been published, and many disorders like inflammatory bowel diseases, psoriasis, allergies and asthma have been found to be associated with a predominantly Th1 or Th2 type of immune response.
But nothing is ever simple, and this dichotomous view of helper T cells is not the complete picture. Another helper T cell subset, Th17, appears to play a role in the pathology of autoimmune diseases such as psoriasis, rheumatoid arthritis, and multiple sclerosis, but also has been proposed to protect against infectious agents, particularly extracellular bacteria and fungi, and to contribute to protection of mucosal sites such as the gut and lungs.
Indeed, the story doesn’t even stop there; immunologists now speak not only of Th1, Th2, and Th17 cells, but also of regulatory T cells and most recently, Th9 and Th22 subsets!
I’ll discuss the clinical relevance of Th17 and regulatory T cells a bit more in future posts, but for now, let me only comment that I feel as though I’m back in the 1990’s when I hear self-proclaimed didacts continuing to adhere to the simplistic Th1/Th2 paradigm. True, the discovery of additional helper T cell subsets can be bewildering and their precise contributions to host protection and pathology are still unfolding, but we must keep stride with research discoveries if we are to nimbly leverage them in our continuing quest to improve our diagnosis (and intervention) of perplexing and debilitating health issues.
This is why you will find IL-17 among the cytokines assessed in several of NeuroScience’s Stimulated Cytokine profiles. If a patient’s white blood cells express elevated levels of IL-17, it helps narrow down possible root causes underlying the patient’s symptoms, such as immune activation in the gut, a fungal infection, or an autoimmune disorder in which Th17 cells have been implicated.
It’s not necessarily an instant diagnosis, but it sheds light where previously there was none.
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