Regulation of T helper type 2 cell immunity by interleukin-4 and interleukin-13

Type 2 cytokine responses are typical of immune reactions to parasitic helm inth infections, allergies, and asthma, and are characterised by the produc tion of the cytokines interleukin (IL)-4, IL-5, IL-9, and IL-13 by subsets of T helper type 2 (Th2) cells. These cytokines form a complex network of m olecular and cellular interactions that mediate protective immunity to worm infection, but also induce inappropriate inflammatory responses to allergi c challenge. Although considerable attention has been given to the roles pl ayed by IL-4 in Th2 responses, the identification of the related cytokine I L-13 has led to a re-evaluation of how these two molecules combine in the g eneration of Th2 immunity. Recent reports have highlighted that in certain challenges, IL-4 and IL-13 act in combination to ensure the rapid onset of a Th2-like response. However, these studies have also identified specific r esponses that are attributable to the individual cytokines. For example, IL -13 appears to play a more dominant role than IL-4 in the expulsion of cert ain gastrointestinal parasites. In contrast, following schistosome infectio n, IL-13 induces a detrimental hepatic fibrosis, while IL-4 protects agains t endotoxemia. These results emphasise the complexity of the cytokine netwo rk, and highlight the care that needs to be taken when designing therapeuti c intervention. (C) 2000 Elsevier Science Inc. All rights reserved.