Dual and Opposite Actions of Cytokines in Autoimmune Inflammatory Demyelination The biological actions of cytokines in the immune system and specifically in autommunity

The biological actions of cytokines in the immune system and specifically in autommunity have been carefully studied in the last few decades [1], in particular after Mosmann and Coffman observed that certain T helper cell populations could be categorised based on the cytokines they produce [2]. It was perhaps inevitable that progress in our knowledge of cytokine biology would generate simplified paradigms that have been challenged and refined over time. In the early stages of the definition of Th1 and Th2 cells, it was readily acknowledged by Mosmann and Coffman that “Further divisions of helper T cells may have to be recognized before a complete picture of helper T-cell function can be obtained” [3] and this is indeed what happened when Th3 [4] and more recently Th17 [5-7], Th9 [8, 9], and Th22 [10] subsets were recognised. While Th1, Th2 and regulatory T cells display a high degree of stability and can even enter the pool of memory cells, Th17 and other newly described populations appear to not truly represent a stable committed lineage. It now appears most likely that significant plasticity in T cell function enables them to produce even more varied combinations of cytokines that are “customised” to the systemic and local requirement of the immune system [11, 12].