Commensal bacterial cells outnumber human cells up to 10-fold
[1]. A human can be viewed as a “super organism” [1] consisting of
human and bacterial cells. These cells are considered by some as a
distinct “organ” [2] that interacts extensively with the rest of the
human body [3]. In particular, the microbiota interacts with the
immune system and can affect inflammation within the body [3],
[4]. Decreased diversity of gut microbiota has been noted in a twin
study of patients with inflammatory bowel disease [5]. Some
anaerobic bacteria may be associated with the development of
colitis in animal models which are immune-deficient [6]. Experiments
in germ-free animal models introduced to different microorganisms
suggests a relationship between the microbiota and rheumatoid arthritis [7]. Significant differences exist between
psoriatic skin and normal skin belonging to the same individual [8].
Tumor necrosis factor a (TNF- a) is a pro-inflammatory cytokine
released by immune cells that trigger a wide range of responses
including inflammation, cell apoptosis, and maturation of immune
cells [9]. TNF-a is an immune mediator that has also been linked
with inflammatory bowel disease, rheumatologic conditions, and
even depression [10]. The role of TNF is especially clear in autoimmune
diseases such as ulcerative colitis and Crohn's disease and
treatment of patients with TNF-a inhibitors effectively slow the
progression of disease [11] [12], however, they also increase the
patient's susceptibility to infections, especially reactivation of
latent mycobacterial infection [13].