All animals have some way to fight off infections by bacteria, viruses, and parasites. If they didn’t, they would soon die. In mammals, this system is quite complex, and includes two main branches. One, the adaptive immune system, learns about infections the first time they are encountered, and then can deal with them quickly if they come back. This is the system that is used in vaccination. The other system, the innate immune system, has a fixed set of responses, and deals with things that look like they might be dangerous, even though the body has never encountered them before. Today’s paper, by a team led by Kazuyo Moro and Shigeo Koyasu at Keio Medical School, reports more discoveries about the innate immune system.
The immune system includes cells called helper T-cells, which secrete substances, called cytokines, that provoke strong immune responses. If these cells respond to the wrong sort of thing, it can cause serious allergies, and an over-reaction can be fatal, leading to a so-called cytokine storm. There are two main types of helper T-cells, as far as I can tell from this article, TH1 and TH2. However, in the years since they were discovered, many cell types have been found to perform a similar function to TH2 cells, so that the name is now being used to refer to a function, rather than a cell type.
This paper reports the discovery of a new group of TH2-type cells, fat-associated lymphocyte clusters (FALCs), which are clusters of fat cells and natural helper cells, a kind of lymphocyte, found along blood vessels near the intestines. The cells seem to be involved in, at least, responding to parasitic infections of the gut, provoking other cells to react in a way that clears the parasites out of the gut. The authors call them natural helper cells, as they have none of the characteristics of T cells.
So, why is this important? Well, an entirely new class of immune cells is a significant discovery. It’s important to understand the immune system as a whole, and in order to do that we need to know what cells make it up. The better we understand the immune system, the better we can handle it when treating infections and the like. Of course, as the cells have only just been discovered, their full importance is not yet known, so the ultimate significance of this discovery is still uncertain. Science is often like that.
Natural helper cells (Editor’s summary)
Immunology: The expanding TH2 universe (News and Views article: Nature 463, 434-435 (28 January 2010) | doi:10.1038/463434a; Published online 27 January 2010)
Innate production of TH2 cytokines by adipose tissue-associated c-Kit+Sca-1+ lymphoid cells (Original paper: Nature 463, 540-544 (28 January 2010) | doi:10.1038/nature08636; Received 6 October 2009; Accepted 5 November 2009; Published online 20 December 2009)