Chronic mucocutaneous candidiasis disease (CMCD) is characterized by recurrent or persistent infections of the skin, nails, oral and genital mucosae caused by Candida albicans and, to a lesser extent, Staphylococcus aureus, in patients with no other infectious or autoimmune manifestations. We report two genetic etiologies of CMCD: autosomal recessive deficiency in the cytokine receptor, interleukin-17 receptor A (IL-17RA), and autosomal dominant deficiency of the cytokine IL-17F. IL-17RA deficiency is complete, abolishing cellular responses to IL-17A and IL-17F homo- and heterodimers. By contrast, IL-17-F deficiency is partial, with mutant IL-17F-containing homo- and heterodimers displaying impaired, but not abolished activity. These experiments of nature indicate that human IL-17A and IL-17F are essential for mucocutaneous immunity against C. albicans, but otherwise largely redundant.

Myostatin is a secreted protein that normally functions as a negative regulator of muscle growth. Agents capable of blocking the myostatin signaling pathway could have important applications for treating human muscle degenerative diseases as well as for enhancing livestock production. Here we describe a potent myostatin inhibitor, a soluble form of the activin type IIB receptor (ACVR2B), which can cause dramatic increases in muscle mass (up to 60% in 2 weeks) when injected into wild-type mice. Furthermore, we show that the effect of the soluble receptor is attenuated but not eliminated in Mstn ؊/؊ mice, suggesting that at least one other ligand in addition to myostatin normally functions to limit muscle growth. Finally, we provide genetic evidence that these ligands signal through both activin type II receptors, ACVR2 and ACVR2B, to regulate muscle growth in vivo. Mice carrying a targeted mutation in the myostatin gene have muscles that are about twice the normal size as a result of a combination of muscle fiber hyperplasia and hypertrophy (2). Myostatin appears to play a similar role in other species as well; naturally occurring mutations in the myostatin gene have been shown to be responsible for the double-muscling phenotype in cattle (3-6), and recent studies have demonstrated that a human baby with approximately twice the normal muscle mass is also homozygous for a loss-of-function mutation in the MSTN gene (7). These findings have raised the possibility that agents capable of targeting the myostatin signaling pathway may be useful for increasing muscle mass for both agricultural and human therapeutic applications. In this regard, loss of myostatin signaling has been shown to have beneficial effects in mouse models of muscle degenerative (8, 9) and metabolic (10) diseases.Various myostatin-binding proteins have been identified that are capable of inhibiting myostatin activity in vitro (8,(11)(12)(13)(14)(15)(16). Two of these proteins, the JA16 neutralizing monoclonal antibody (Ab) directed against myostatin (8, 15) and a mutant form of the myostatin propeptide resistant to members of the BMP-1͞tolloid family of metalloproteases (16), have been shown to be capable of increasing muscle mass by Ϸ25% when administered to wild-type (WT) mice. To determine whether these increases in muscle growth are the maximal achievable by targeting this signaling pathway, we sought additional myostatin inhibitors that might have a broader specificity in their ability to target additional members of the TGF-␤ superfamily. Previous studies have demonstrated that myostatin is capable of binding the two activin type II receptors, ACVR2B and, to a lesser extent, ACVR2, in transfected COS cells (11,17). Moreover, transgenic mice in which a myosin light chain promoter͞ enhancer was used to express a truncated form of ACVR2B in skeletal muscle were found to have dramatic increases in muscle mass (11). Because the activin type II receptors have been shown to be capable of binding a number of other TGF-␤ family members in addition to ...

Myostatin is a transforming growth factor ␤ family member that acts as a negative regulator of skeletal muscle growth. Myostatin circulates in the blood of adult mice in a noncovalently held complex with other proteins, including its propeptide, which maintain the C-terminal dimer in a latent, inactive state. This latent form of myostatin can be activated in vitro by treatment with acid; however, the mechanisms by which latent myostatin is activated in vivo are unknown. Here, we show that members of the bone morphogenetic protein-1͞tolloid (BMP-1͞TLD) family of metalloproteinases can cleave the myostatin propeptide in this complex and can thereby activate latent myostatin. Furthermore, we show that a mutant form of the propeptide resistant to cleavage by BMP-1͞TLD proteinases can cause significant increases in muscle mass when injected into adult mice. These findings raise the possibility that members of the BMP-1͞TLD family may be involved in activating latent myostatin in vivo and that molecules capable of inhibiting these proteinases may be effective agents for increasing muscle mass for both human therapeutic and agricultural applications.

No abstract

IL-17A and IL-17F are related homodimeric proteins of the IL-17 family produced by Th17 cells. In this study, we show that mouse Th17 cells also produce an IL-17F/A heterodimeric protein. Whereas naive CD4+ T cells differentiating toward the Th17 cell lineage expressed IL-17F/A in higher amounts than IL-17A/A homodimer and in lower amounts than IL-17F/F homodimer, differentiated Th17 cells expressed IL-17F/A in higher amounts than either homodimer. In vitro, IL-17F/A was more potent than IL-17F/F and less potent than IL-17A/A in regulating CXCL1 expression. Neutralization of IL-17F/A with an IL-17A-specific Ab, and not with an IL-17F-specific Ab, reduced the majority of IL-17F/A-induced CXCL1 expression. To study these cytokines in vivo, we established a Th17 cell adoptive transfer model characterized by increased neutrophilia in the airways. An IL-17A-specific Ab completely prevented Th17 cell-induced neutrophilia and CXCL5 expression, whereas Abs specific for IL-17F or IL-22, a cytokine also produced by Th17 cells, had no effects. Direct administration of mouse IL-17A/A or IL-17F/A, and not IL-17F/F or IL-22, into the airways significantly increased neutrophil and chemokine expression. Taken together, our data elucidate the regulation of IL-17F/A heterodimer expression by Th17 cells and demonstrate an in vivo function for this cytokine in airway neutrophilia.

IL-17F and IL-17A are members of the IL-17 pro-inflammatory cytokine family. IL-17A has been implicated in the pathogenesis of autoimmune diseases. IL-17F is a disulfidelinked dimer that contains a cysteine-knot motif. We hypothesized that IL-17F and IL-17A could form a heterodimer due to their sequence homology and overlapping pattern of expression. We evaluated the structure of recombinant IL-17F and IL-17A proteins, as well as that of natural IL-17F and IL-17A derived from activated human CD4؉ T cells, by enzyme-linked immunosorbent assay, immunoprecipitation followed by Western blotting, and mass spectrometry. We find that both IL-17F and IL-17A can form both homodimeric and heterodimeric proteins when expressed in a recombinant system, and that all forms of the recombinant proteins have in vitro functional activity. Furthermore, we find that in addition to the homodimers of IL-17F and IL-17A, activated human CD4؉ T cells also produce the IL-17F/IL-17A heterodimer. These data suggest that the IL-17F/IL-17A heterodimer may contribute to the T cell-mediated immune responses.Interleukins 17F 3 and 17A (IL-17A) are closely related members of the IL-17 cytokine family, and share 50% amino acid identity. Studies in the mouse have identified Th17 cells as a distinct CD4ϩ T cell lineage that is defined by the production of IL-17F and IL-17A (1-7). IL-6 and transforming growth factor-␤ (TGF-␤) are required for the differentiation of naïve CD4ϩ T cells to Th17 cells (1,8), which are maintained in the presence of IL-23 and IL-1␤. Conversely, IL-4 and interferon-␥ can inhibit the development of Th17 cells (9, 10). Th17 cells have been implicated in the pathology of mouse autoimmune disease models (2).Expression of IL-17F and IL-17A has been detected in activated human peripheral blood lymphocytes. It has been shown by reverse transcriptase-PCR experiments that the cytokines are expressed in activated human CD4ϩ T cells (11,12). Expression of IL-17F and IL-17A has also been observed in tissue samples from various autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, psoriasis, inflammatory bowel disease, and asthma (2, 3, 13-22).The crystal structure of IL-17F has been solved and shows that the protein forms a disulfide-linked dimeric glycoprotein (23). IL-17A is also a disulfide-linked homodimeric glycoprotein (24), although crystal structure or data defining the precise subunit interactions are lacking. The IL-17F homodimer includes a classical cysteine knot motif, which is found in the TGF-␤, bone morphogenetic protein, and nerve growth factor superfamilies (25, 26). One difference in the cysteine knot motif of IL-17F compared with the other known cysteine knot protein families is that it only utilizes four cysteines instead of the classical six cysteines to form the knot.There have been reports that some of the cysteine knot family members can exist as heterodimers in vivo. TGF-␤1.2 and -␤2.3 were identified in bovine bone extracts, whereas inhibin and activin AB have been found in gonadal fluids (27...

IL-17A and IL-17F, produced by the Th17 CD4+ T cell lineage, have been linked to a variety of inflammatory and autoimmune conditions. We recently reported that activated human CD4+ T cells produce not only IL-17A and IL-17F homodimers but also an IL-17F/IL-17A heterodimeric cytokine. All three cytokines can induce chemokine secretion from bronchial epithelial cells, albeit with different potencies. In this study, we used small interfering RNA and Abs to IL-17RA and IL-17RC to demonstrate that heterodimeric IL-17F/IL-17A cytokine activity is dependent on the IL-17RA/IL-17RC receptor complex. Interestingly, surface plasmon resonance studies indicate that the three cytokines bind to IL-17RC with comparable affinities, whereas they bind to IL-17RA with different affinities. Thus, we evaluated the effect of the soluble receptors on cytokine activity and we find that soluble receptors exhibit preferential cytokine blockade. IL-17A activity is inhibited by IL-17RA, IL-17F is inhibited by IL-17RC, and a combination of soluble IL-17RA/IL-17RC receptors is required for inhibition of the IL-17F/IL-17A activity. Altogether, these results indicate that human IL-17F/IL-17A cytokine can bind and signal through the same receptor complex as human IL-17F and IL-17A. However, the distinct affinities of the receptor components for IL-17A, IL-17F, and IL-17F/IL-17A heterodimer can be exploited to differentially affect the activity of these cytokines.

T-helper 17 (Th17) cells are a new lineage of CD4(+) T cells that are characterized by their production of interleukin-17A (IL-17A). Recent studies show that these cells can also express IL-17F, IL-22, and IL-21. IL-17A and IL-17F can form a heterodimeric cytokine, which mediates biological activities, at least in part, through shared receptors with IL-17A and IL-17F homodimers. The cytokines made by Th17 cells represent three distinct gene families, highlighting the unique biology of these cells. Accumulating data support a role for Th17 cells and these cytokines in inflammatory processes and in animal models of autoimmunity or inflammation. Emerging data in clinical trials support our understanding of the importance of Th17 cells in inflammatory disease. Future clinical studies will allow us to evaluate the role of each cytokine independently in contributing to human diseases with immune-mediated pathologies and to design optimal cytokine-targeted therapies for these diseases.