text: Butyrate is essential to host immune homeostasis. Although the role and importance of butyrate in the gut is not fully understood, many researchers argue that a depletion of butyrate-producing bacteria in patients with several vasculitic conditions is essential to the pathogenesis of these disorders. A depletion of butyrate in the gut is typically caused by an absence or depletion of butyrate-producing-bacteria (BPB). This depletion in BPB leads to microbial dysbiosis. This is characterized by an overall low biodiversity and a depletion of key butyrate-producing members. Butyrate is an essential microbial metabolite with a vital role as a modulator of proper immune function in the host. It has been shown that children lacking in BPB are more susceptible to allergic disease and Type 1 Diabetes. Butyrate is also reduced in a diet low in dietary fiber, which can induce inflammation and have other adverse affects insofar as these short-chain fatty acids activate PPAR-γ.
  Butyrate exerts a key role for the maintenance of immune homeostasis both locally (in the gut) and systemically (via circulating butyrate). It has been shown to promote the differentiation of regulatory T cells. In particular, circulating butyrate prompts the generation of extrathymic regulatory T cells. The low-levels of butyrate in human subjects could favor reduced regulatory T cell-mediated control, thus promoting a powerful immuno-pathological T-cell response. On the other hand, gut butyrate has been reported to inhibit local pro-inflammatory cytokines. The absence or depletion of these BPB in the gut could therefore be a possible aide in the overly-active inflammatory response. Butyrate in the gut also protects the integrity of the intestinal epithelial barrier. Decreased butyrate levels therefore lead to a damaged or dysfunctional intestinal epithelial barrier.
  In a 2013 research study conducted by Furusawa et al., microbe-derived butyrate was found to be essential in inducing the differentiation of colonic regulatory T cells in mice. This is of great importance and possibly relevant to the pathogenesis and vasculitis associated with many inflammatory diseases because regulatory T cells have a central role in the suppression of inflammatory and allergic responses. In several research studies, it has been demonstrated that butyrate induced the differentiation of regulatory T cells in vitro and in vivo. The anti-inflammatory capacity of butyrate has been extensively analyzed and supported by many studies. It has been found that microorganism-produced butyrate expedites the production of regulatory T cells, although the specific mechanism by which it does so unclear. More recently, it has been shown that butyrate plays an essential and direct role in modulating gene expression of cytotoxic T-cells. Butyrate also has an anti-inflammatory effect on neutrophils, reducing their migration to wounds. This effect is mediated via the receptor Hydroxycarboxylic acid receptor 1|
  In the gut microbiomes found in the class Mammalia, omnivores and herbivores have butyrate-producing bacterial communities dominated by the butyryl-CoA:acetate CoA-transferase pathway, whereas carnivores have butyrate-producing bacterial communities dominated by the butyrate kinase pathway.
  The odor of butyric acid, which emanates from the sebaceous follicles of all mammals, works on the tick as a signal.