IL-23: changing the verdict on IL-12 function in inflammation and autoimmunity

Anti-Interleukin-23 Autoantibodies in Adult-Onset Immunodeficiency

BACKGROUND

Autoantibodies against interleukin-12 (anti-interleukin-12) are often identified in patients with thymoma, but opportunistic infections develop in only some of these patients. Interleukin-12 (with subunits p40 and p35) shares a common subunit with interleukin-23 (subunits p40 and p19). In a patient with disseminated Burkholderia gladioli infection, the identification of both anti-interleukin-23 and anti-interleukin-12 prompted further investigation.

METHODS

Among the patients (most of whom had thymoma) who were known to have anti-interleukin-12, we screened for autoantibodies against interleukin-23 (anti-interleukin-23). To validate the potential role of anti-interleukin-23 with respect to opportunistic infection, we tested a second cohort of patients with thymoma as well as patients without either thymoma or known anti-interleukin-12 who had unusual infections.

RESULTS

Among 30 patients with anti-interleukin-12 who had severe mycobacterial, bacterial, or fungal infections, 15 (50%) also had autoantibodies that neutralized interleukin-23. The potency of such neutralization was correlated with the severity of these infections. The neutralizing activity of anti-interleukin-12 alone was not associated with infection. In the validation cohort of 91 patients with thymoma, the presence of anti-interleukin-23 was associated with infection status in 74 patients (81%). Overall, neutralizing anti-interleukin-23 was detected in 30 of 116 patients (26%) with thymoma and in 30 of 36 patients (83%) with disseminated, cerebral, or pulmonary infections. Anti-interleukin-23 was present in 6 of 32 patients (19%) with severe intracellular infections and in 2 of 16 patients (12%) with unusual intracranial infections, including Cladophialophora bantiana and Mycobacterium avium complex.

CONCLUSIONS

Among patients with a variety of mycobacterial, bacterial, or fungal infections, the presence of neutralizing anti-interleukin-23 was associated with severe, persistent opportunistic infections. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Anti-cytokine autoantibodies: mechanistic insights and disease associations

Anti-cytokine autoantibodies (ACAAs) are increasingly recognized as modulating disease severity in infection, inflammation and autoimmunity. By reducing or augmenting cytokine signalling pathways or by altering the half-life of cytokines in the circulation, ACAAs can be either pathogenic or disease ameliorating. The origins of ACAAs remain unclear. Here, we focus on the most common ACAAs in the context of disease groups with similar characteristics. We review the emerging genetic and environmental factors that are thought to drive their production. We also describe how the profiling of ACAAs should be considered for the early diagnosis, active monitoring, treatment or sub-phenotyping of diseases. Finally, we discuss how understanding the biology of naturally occurring ACAAs can guide therapeutic strategies.

The Role of Granulocyte-Macrophage Colony-Stimulating Factor in Murine Models of Multiple Sclerosis

Multiple sclerosis (MS) is an immune-mediated disease that predominantly impacts the central nervous system (CNS). Animal models have been used to elucidate the underpinnings of MS pathology. One of the most well-studied models of MS is experimental autoimmune encephalomyelitis (EAE). This model was utilized to demonstrate that the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) plays a critical and non-redundant role in mediating EAE pathology, making it an ideal therapeutic target. In this review, we will first explore the role that GM-CSF plays in maintaining homeostasis. This is important to consider, because any therapeutics that target GM-CSF could potentially alter these regulatory processes. We will then focus on current findings related to the function of GM-CSF signaling in EAE pathology, including the cell types that produce and respond to GM-CSF and the role of GM-CSF in both acute and chronic EAE. We will then assess the role of GM-CSF in alternative models of MS and comment on how this informs the understanding of GM-CSF signaling in the various aspects of MS immunopathology. Finally, we will examine what is currently known about GM-CSF signaling in MS, and how this has promoted clinical trials that directly target GM-CSF.

IL-12 family cytokines: immunological playmakers

The interleukin 12 (IL-12) family is unique in having the only heterodimeric cytokines, including IL-12, IL-23, IL-27 and IL-35. This feature endows these cytokines with a unique set of connections and functional interactions not shared by other cytokine families. Despite sharing many structural features and molecular partners, cytokines of the IL-12 family mediate surprisingly diverse functional effects. Here we discuss the unique and unusual structural and functional characteristics of this cytokine family. We outline how cells might interpret seemingly similar cytokine signals to give rise to the diverse functional outcomes that characterize this cytokine family. We also discuss the therapeutic implications of this complexity.

RORγt drives production of the cytokine GM-CSF in helper T cells, which is essential for the effector phase of autoimmune neuroinflammation

Although the role of the T(H)1 and T(H)17 subsets of helper T cells as disease mediators in autoimmune neuroinflammation remains a subject of some debate, none of their signature cytokines are essential for disease development. Here we report that interleukin 23 (IL-23) and the transcription factor RORγt drove expression of the cytokine GM-CSF in helper T cells, whereas IL-12, interferon-γ (IFN-γ) and IL-27 acted as negative regulators. Autoreactive helper T cells specifically lacking GM-CSF failed to initiate neuroinflammation despite expression of IL-17A or IFN-γ, whereas GM-CSF secretion by Ifng(-/-)Il17a(-/-) helper T cells was sufficient to induce experimental autoimmune encephalomyelitis (EAE). During the disease effector phase, GM-CSF sustained neuroinflammation via myeloid cells that infiltrated the central nervous system. Thus, in contrast to all other known helper T cell-derived cytokines, GM-CSF serves a nonredundant function in the initiation of autoimmune inflammation regardless of helper T cell polarization.

Absence of IL-23p19 in donor allogeneic cells reduces mortality from acute GVHD

The p19 dimer of interleukin 23 (IL-23) has been reported to have a major role in the pathogenesis of many experimental and clinical autoimmune diseases and may also have a prominent role in transplantation. We reasoned that deficiency of p19 in the allogeneic donor transplant might reduce the inflammation caused by acute GVHD (aGVHD). The major histocompatibility complex-2 (H2(d)) BALB/c mice were subjected to 8.5 Gy TBI, followed by transplantation with 10 x 10(6) BM and 2.5 x 10(6) spleen cells from H2(d) BALB/c, H2(b) C57Bl/6 (B6) or H2(b) p19-/- donors. In all, 75% of the p19-/- transplanted mice survived, compared with only 12.5% of the B6 transplanted mice. This superior survival is correlated with significantly less severe aGVHD, absence of p19 after transplantation, less upregulation of mRNA and lower serum levels of IL-17 as compared with the B6 transplants. TBI alone significantly upregulated transforming growth factor-beta (TGF-beta), IL-6 and p19 mRNA levels in host BALB/c mice, possibly providing the milieu to induce IL-17 in p19-/- donor cells. IL-22, another cytokine, the induction of which in T-helper 17 (Th17) cells is supported by p19, was upregulated in BALB/c hosts but not in transplanted B6 or p19 donor cells, and may not have had a major role in modifying aGVHD.

IL-22 is expressed by Th17 cells in an IL-23-dependent fashion, but not required for the development of autoimmune encephalomyelitis

Lately, IL-17-secreting Th cells have received an overwhelming amount of attention and are now widely held to be the major pathogenic population in autoimmune diseases. In particular, IL-22-secreting Th17 cells were shown to specifically mark the highly pathogenic population of self-reactive T cells in experimental autoimmune encephalomyelitis (EAE). As IL-17A itself was found to only play a minor role during the development of EAE, IL-22 is now postulated to contribute to the pathogenic function of Th17 cells. The goal of this study was to determine the role and function of IL-22 during the development of CNS autoimmunity in vivo. We found that CNS-invading encephalitogenic Th17 cells coexpress IL-22 and that IL-22 is specifically induced by IL-23 in autoimmune-pathogenic CD4+ T cells in a time- and dose-dependent manner. We next generated IL-22-/- mice, which--in contrast to the prediction that expression of inflammatory cytokines by CNS-invading T cells inevitably confers pathogenic function--turned out to be fully susceptible to EAE. Taken together, we show that self-reactive Th cells coexpress IL-17 and IL-22, but that the latter also does not appear to be directly involved in autoimmune pathogenesis of the CNS.

Early inflammatory responses direct chronic autoimmunity development in the heart following coxsackievirus infection

Coxsackievirus infections are a major cause of chronic autoimmune myocarditis, a known precursor to dilated cardiomyopathy. Dilated cardiomyopathy leads to heart failure and is responsible for nearly half of all heart transplant cases. The induction of chronic autoimmunity following coxsackievirus infection is governed by the interplay of several genetic and immunological factors. In this review, we will focus on how the innate immune response to viral infection directs a cascade of events that ultimately results in chronic autoimmune heart disease.