Type I interferon responses in rhesus macaques prevent SIV infection and slow disease progression.

Inflammation in HIV infection is predictive of non-AIDS morbidity and death, higher set point plasma virus load and virus acquisition; thus, therapeutic agents are in development to reduce its causes and consequences. However, inflammation may simultaneously confer both detrimental and beneficial effects. This dichotomy is particularly applicable to type I interferons (IFN-I) which, while contributing to innate control of infection, also provide target cells for the virus during acute infection, impair CD4 T-cell recovery, and are associated with disease progression. Here we manipulated IFN-I signalling in rhesus macaques (Macaca mulatta) during simian immunodeficiency virus (SIV) transmission and acute infection with two complementary in vivo interventions. We show that blockade of the IFN-I receptor caused reduced antiviral gene expression, increased SIV reservoir size and accelerated CD4 T-cell depletion with progression to AIDS despite decreased T-cell activation. In contrast, IFN-α2a administration initially upregulated expression of antiviral genes and prevented systemic infection. However, continued IFN-α2a treatment induced IFN-I desensitization and decreased antiviral gene expression, enabling infection with increased SIV reservoir size and accelerated CD4 T-cell loss. Thus, the timing of IFN-induced innate responses in acute SIV infection profoundly affects overall disease course and outweighs the detrimental consequences of increased immune activation. Yet, the clinical consequences of manipulation of IFN signalling are difficult to predict in vivo and therapeutic interventions in human studies should be approached with caution.

Critical role of the endogenous interferon ligand-receptors in type I and type II interferons response.

Separate ligand-receptor paradigms are commonly used for each type of interferon (IFN). However, accumulating evidence suggests that type I and type II IFNs may not be restricted to independent pathways. Using different cell types deficient in IFNAR1, IFNAR2, IFNGR1, IFNGR2 and IFN-γ, we evaluated the contribution of each element of the IFN system to the activity of type I and type II IFNs. We show that deficiency in IFNAR1 or IFNAR2 is associated with impairment of type II IFN activity. This impairment, presumably resulting from the disruption of the ligand-receptor complex, is obtained in all cell types tested. However, deficiency of IFNGR1, IFNGR2 or IFN-γ was associated with an impairment of type I IFN activity in spleen cells only, correlating with the constitutive expression of type II IFN (IFN-γ) observed on those cells. Therefore, in vitro the constitutive expression of both the receptors and the ligands of type I or type II IFN is critical for the enhancement of the IFN activity. Any IFN deficiency can totally or partially impair IFN activity, suggesting the importance of type I and type II IFN interactions. Taken together, our results suggest that type I and type II IFNs may regulate biological activities through distinct as well as common IFN receptor complexes.

Mutation of the IFNAR-1 receptor binding site of human IFN-alpha2 generates type I IFN competitive antagonists.

Type I interferons (IFNs) are multifunctional cytokines that activate cellular responses by binding a common receptor consisting of two subunits, IFNAR-1 and IFNAR-2. Although the binding of IFNs to IFNAR-2 is well characterized, the binding to the lower affinity IFNAR-1 remains less well understood. Previous reports identified a region of human IFN-alpha2 on the B and C helices ("site 1A": N65, L80, Y85, Y89) that plays a key role in binding IFNAR-1 and contributes strongly to differential activation by various type I IFNs. The current studies demonstrate that residues on the D helix are also involved in IFNAR-1 binding. In particular, residue 120 (Arg in IFN-alpha2; Lys in IFN-alpha2/alpha1) appears to be a "hot-spot" residue: substitution by alanine significantly decreased biological activity, and the charge-reversal mutation of residue 120 to Glu caused drastic loss of antiviral and antiproliferative activity for both IFN-alpha2 and IFN-alpha2/alpha1. Mutations in residues of helix D maintained their affinity for IFNAR-2 but had decreased affinity for IFNAR-1. Single-site or multiple-site mutants in the IFNAR-1 binding site that had little or no detectable in vitro biological activity were capable of blocking in vitro antiviral and antiproliferative activity of native IFN-alpha2; i.e., they are type I IFN antagonists. These prototype IFN antagonists can be developed further for possible therapeutic use in systemic lupus erythematosus, and analogous molecules can be designed for use in animal models.

Interferon at 50: new molecules, new potential, new (and old) questions.

Type I interferons (IFNs) are a family of cytokines defined by their antiviral activity but with a broad spectrum of biological activities, including antiproliferative, antitumor, and immunomodulatory effects. Mirroring these activities are diverse therapeutic applications to viral infections, antitumor therapy, and multiple sclerosis. The type I IFNs all signal through a common heterodimeric receptor. The existence of such a large family of cytokines (17 human IFNs) activating a common receptor is unusual. Moreover, the IFNs vary in their relative potency in different assays and are not functionally equivalent. How this functional variation is mediated through a common receptor has not been understood. Reports have now highlighted the interaction of IFNs with the low-affinity receptor subunit IFNAR-1 as a surprising key to their differential activity, particularly regarding antiproliferative and antitumor activities. Two groups have used contrasting approaches to produce variant IFN-alpha proteins with novel activity profiles. These advances portend enhanced therapeutic possibilities based on the better understanding of IFN-receptor interactions, while raising interesting mechanistic questions.

The Class II cytokine receptor (CRF2) family: overview and patterns of receptor-ligand interactions.

Expanded genomic information has driven the discovery of new members of the human Class II family of cytokine receptors (CRF2), which now includes 12 proteins. The corresponding cytokines have been identified, paired with their receptors and initially characterized for function. These cytokines include: a new human Type I IFN, IFN-kappa; molecules related to IL-10 (IL-19, IL-20, IL-22, IL-24, IL-26); and IFN-lambdas (IL-28/29), which have antiviral and cell stimulatory activities reminiscent of Type I IFNs, but act through a distinct receptor. In response to ligand binding, the CRF2 proteins form heterodimers, leading to cytokine-specific cellular responses; these diverse physiological functions are just beginning to be explored. Progress in structural and mutational analysis of ligand-receptor interactions now presents a more reliable framework for understanding receptor-ligand interactions, and for predicting key regions in less well studied members of the CRF2 family. The relationships between the CRF2 proteins will be summarized, as will the progress in identifying patterns of receptor interactions with ligands.

Full house: 12 receptors for 27 cytokines.

With the sequencing of the human genome nearing completion, it appears that all members of the class II cytokine receptor family (CRF2) have been identified and partially characterized. The entire family is composed of exactly one dozen members. Eleven of them combine as various heterodimers to transduce signals across the cellular membrane for 27 cytokines divided into four structurally related groups: 6 cytokines of the IL-10 family, 17 type I IFNs, 1 type II IFN and 3 IFN-lambdas. The last CRF2 member is the soluble receptor which can neutralize the action of one of the cytokines of the IL-10 family, IL-22. Although the extracellular domains of all CRF2 proteins reveal primary and structural homology, their intracellular domains are very dissimilar. Nevertheless, signaling events induced through various combinations of CRF2 subunits partially overlap, leading to the induction of overlapping but cytokine-specific biological activities.

Regulatory T cells as central regulators of both autoimmunity and B cell malignancy in New Zealand Black mice.

Regulatory T cells (Tregs) play an important role in protection against autoimmune disease and are also known to be potent inhibitors of anti-tumor immune responses. The New Zealand Black (NZB) mouse is a murine model for both autoimmune diseases, since high levels of autoantibodies are present, and human CLL, due to the expansion of malignant B-1 cells. In this study, we examined the functional role of CD4(+)CD25(+) Foxp3(+) Tregs in these different manifestations. Flow cytometric analysis showed increased levels of Tregs in NZB mice compared to healthy C57Bl/6 controls. Aged NZB mice that have developed a B-1 cell malignancy identified as IgM(+)CD5(+), have the most pronounced increase in Tregs. Ex vivo treatment of splenocytes from NZB mice with IFN-alpha resulted in a decrease in the frequency of Tregs and malignant B-1 cells. In vivo treatment of both NZB and C57Bl/6 mice with poly (I:C), a potent inducer of IFN-alpha, also led to a decrease in the levels of Tregs and malignant B-1 cells (NZB only) while amplifying autoimmune manifestations. These results indicate that while high levels of Tregs found in NZB mice might suppress a more severe autoimmune disease, they may also contribute to the development of the B cell malignancy.

IFN-lambdas mediate antiviral protection through a distinct class II cytokine receptor complex.

We report here the identification of a ligand-receptor system that, upon engagement, leads to the establishment of an antiviral state. Three closely positioned genes on human chromosome 19 encode distinct but paralogous proteins, which we designate interferon-lambda1 (IFN-lambda1), IFN-lambda2 and IFN-lambda3 (tentatively designated as IL-29, IL-28A and IL-28B, respectively, by HUGO). The expression of IFN-lambda mRNAs was inducible by viral infection in several cell lines. We identified a distinct receptor complex that is utilized by all three IFN-lambda proteins for signaling and is composed of two subunits, a receptor designated CRF2-12 (also designated as IFN-lambdaR1) and a second subunit, CRF2-4 (also known as IL-10R2). Both receptor chains are constitutively expressed on a wide variety of human cell lines and tissues and signal through the Jak-STAT (Janus kinases-signal transducers and activators of transcription) pathway. This receptor-ligand system may contribute to antiviral or other defenses by a mechanism similar to, but independent of, type I IFNs.