What is the role of T and B cells in the pathophysiology of atopic dermatitis (eczema)?

Updated: Mar 13, 2019
  • Author: Brian S Kim, MD, MTR, FAAD; Chief Editor: William D James, MD  more...
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Answer

In healthy individuals, balance exists between important subsets of T cells (eg, Th1, Th2, Th17, Th22). The primary immune dysfunction hypothesis invokes an imbalance in the T cell subsets, with Th2 cells predominating; this results in the production of type 2 cytokines such as interleukin (IL)–4, IL-5, and IL-13, causing an increase in IgE from plasma cells. Later, in persons with chronic AD, the Th1 cells have been shown to predominate. More recently, Th17 cells have been found to be elevated in patients with AD. [9] Although primarily considered a Th2 cell‒associated cytokine-mediated disease, the precise contributions of Th1 and Th17 cell responses remain to be fully defined.

In addition to the role of T and B cells in AD, other innate immune cells have also been implicated in the pathogenesis of AD, including eosinophils and mast cells. [10, 11] More recently, basophils and newly identified innate immune cells called group 2 innate lymphoid cells (ILC2s) have been shown to underlie the pathogenesis of AD. [12, 13, 14, 15, 16] Together, basophils and ILC2s are critical sources of the type 2 cytokines IL-4, IL-5, and IL-13. [12, 13] Further, these cells appear to be potently regulated by a family of epithelial cell‒derived cytokines directly released from damaged keratinocytes, including thymic stromal lymphopoietin (TSLP), IL-25, and IL-33. [17] Taken together, these studies highlight a new paradigm in which, in addition to classical adaptive Th2 cells, innate type 2 immune cells play critical roles in the etiology of AD through interactions with epidermal-derived cytokines.

In terms of AD-associated itch, Th2 cells are known to be significant sources of the itch-inducing cytokine or pruritogen IL-31. [18] Emerging clinical trials data indicate that blocking this pathway may be a key mechanism by which atopic itch can be treated clinically. Additionally, a 2017 study identified that neuronal, rather than immune, signaling of the type 2 cytokines IL-4 and IL-13 critically regulate AD-associated itch. [19] Indeed, the dual IL-4 and IL-13 blocker, dupilumab, has emerged as a highly effective treatment for AD, which received FDA approval in March of 2017. Thus, blocking cytokine-nerve interactions with targeted biologic therapies has emerged as a novel therapeutic strategy in AD.


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