Human interleukin-12α and EBI3 are cytokines with anti-inflammatory functions

Abstract

Interleukins are secreted proteins that regulate immune responses. Among these, the interleukin 12 (IL-12) family holds a central position in inflammatory and infectious diseases. Each family member consists of an α and a β subunit that together form a composite cytokine. Within the IL-12 family, IL-35 remains particularly ill-characterized on a molecular level despite its key role in autoimmune diseases and cancer. Here we show that both IL-35 subunits, IL-12α and EBI3, mutually promote their secretion from cells but are not necessarily secreted as a heterodimer. Our data demonstrate that IL-12α and EBI3 are stable proteins in isolation that act as anti-inflammatory molecules. Both reduce secretion of proinflammatory cytokines and induce the development of regulatory T cells. Together, our study reveals IL-12α and EBI3, the subunits of IL-35, to be functionally active anti-inflammatory immune molecules on their own. This extends our understanding of the human cytokine repertoire as a basis for immunotherapeutic approaches.

Changes in Serum IL-12 Levels following the Administration of H1-Antihistamines in Patients with Chronic Spontaneous Urticaria

“…The molecular background for the pleiotropic activities mediated by IL-12 cytokines in patients with chronic spontaneous urticaria (CSU) could be attributed to the strict regulation of production, signalling pathways and their effects, as well as cytokine-specific consequences on the same pathophysiological events. Currently, validated structures and experimental models of the p35 and p40 subunits are available, elucidating the assembly and temporal-spatial organization of polypeptide chains and competition for specific receptors associated with JAK/STAT signalling [ 43 , 44 , 60 , 61 ].…”

“…A fundamental contribution to the understanding of the modulation mechanisms of IL-12 family production comes from the β subunit’s ability to regulate the proper folding and assembly of polypeptide chains as a principle in endoplasmic reticulum quality control [ 62 ]. In vivo, IL-12α and IL-12β mutually promote each other’s folding, covalent assembly, secretion, and bioactivity [ 30 , 43 , 44 ]. In the absence of IL-12β, IL-12α misfolds, forming non-native disulfide bonds, and consequently it is retained in cells and subjected to oxidative degradation [ 62 ].…”

“…Recent independent studies have validated the concept that IL-12p35 and IL-12p40 are stable cytokines with independent functions, active as monomers, homodimers, and heterodimers, which can have antagonistic, additive, or synergistic influences on the same biological process [ 43 , 44 ]. IL-12-derived cytokines promote a particular phenotype—for example, Th1 (bioactive IL-12), Th2/anti-inflammatory (antagonistic IL-12(p40)2 homodimers)—in a pathogenic microenvironment [ 61 , 62 , 63 , 64 ].…”

“…The IL-12 family orchestrates inflammation through competition between IL-12p70 and IL-12p40 homodimers for binding to the receptor [7,26]. IL-12p35 suppresses inflammation by inhibiting the expansion of pathogenic Th 1 and Th 17 cells [40][41][42][43][44].…”

“…Investigating the involvement of the IL-12 cytokine family in CSU management is a challenge. The IL-12 family consists of five natural members, namely IL-12, IL-23, IL-27, IL-35, and IL-39, and two synthetic members, IL-X and IL-Y [ 25 , 26 , 27 , 30 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. The members of the IL-12 family, including their structure, specific receptor nature, signalling pathways, target cells, and biological activities, have been extensively studied ( Table 1 ) [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ].…”