Similarities and dissimilarities between asthma and inflammatory bowel diseases

Because both asthma and inflammatory bowel disease are chronic relapsing inflammatory conditions, comparisons are inevitable. Both disorders reflect the convergence of environmental trigger factors in genetically predisposed individuals. The genetic preposition may be on a polygenic basis or on the basis of genetic heterogeneity. Environmental factors that may trigger the expression or relapse in asthma and inflammatory bowel disease include: cigarette smoking (in Crohn's but not in ulcerative colitis), the use of non-steroidal anti-inflammatory drugs in asthma and Crohn's disease), infection and possibly stress. TH lymphocytes are currently believed to be important in asthma and in Crohn's disease but not in ulcerative colitis. IgE-activated eosinophils and mast cells are central to the maintenance of asthma but do not play such a crucial role in inflammatory bowel disease. TH2 cytokines including IL-4 and IL-5 are believed to be important in the inflammatory response of asthma, and TH cytokines are believed to be in Crohn's disease but a TH1 or TH2 subclassification is not currently evident. The hallmark of asthma is increased reactivity of the airways, in terms of bronchoconstriction. Altered physiology also accompanies inflammatory bowel disease but hyperactivity is not an invariable feature. Finally, it is becoming increasingly evident that neural influences modulate inflammatory processes and this is likely to be relevant to both asthma and inflammatory bowel disease.