Introduction
The immune response comprises a complex cascade of reactions that balances effector and regulatory functions.1 While the effector’s arm includes cellular and molecular components responsible for preventing cellular infections and cancer, the regulatory arm is responsible for limiting excessive immune activation to maintain physiologic homeostasis.1 Any uncontrolled process in these components may lead to immune-mediated inflammatory disorders (IMIDs).2-4
The interleukin (IL)-12 family comprises heterodimeric cytokines (IL-12, IL-23, IL-27, IL-35, and IL-39) with a range of functions in promoting and suppressing inflammation and autoimmunity (Figure 1).5 They stimulate immune responses by inducing and activating T cell subpopulations and changing other cell functions that are associated with IMIDs such as psoriasis, psoriatic arthritis, and inflammatory bowel disease.6-8
IL-23 and its role in IMIDs have been recently described and prompted efforts to clarify its relative contribution to immune regulation.8 It is composed of two subunits: p40, also present in IL-12, and p19, which is likewise part of IL-39, that the existence in the human system has yet to be confirmed (Figure 1).5 Studies focusing on signaling pathways propose that IL-23 is secreted mainly by activated dendritic cells (DCs) and macrophages.3,7 However, it has been suggested that different non-immune cells (eg, endothelial cells, keratinocytes [KCs], and synoviocytes) are also able to release IL-23.3
The interleukin (IL)-12 family comprises heterodimeric cytokines (IL-12, IL-23, IL-27, IL-35, and IL-39) with a range of functions in promoting and suppressing inflammation and autoimmunity (Figure 1).5 They stimulate immune responses by inducing and activating T cell subpopulations and changing other cell functions that are associated with IMIDs such as psoriasis, psoriatic arthritis, and inflammatory bowel disease.6-8
IL-23 and its role in IMIDs have been recently described and prompted efforts to clarify its relative contribution to immune regulation.8 It is composed of two subunits: p40, also present in IL-12, and p19, which is likewise part of IL-39, that the existence in the human system has yet to be confirmed (Figure 1).5 Studies focusing on signaling pathways propose that IL-23 is secreted mainly by activated dendritic cells (DCs) and macrophages.3,7 However, it has been suggested that different non-immune cells (eg, endothelial cells, keratinocytes [KCs], and synoviocytes) are also able to release IL-23.3
