Genetic ablation of arginase 1 in macrophages and neutrophils enhances clearance of an arthritogenic alphavirus

Human papillomavirus e7 oncoprotein transgenic skin develops an enhanced inflammatory response to 2,4-dinitrochlorobenzene by an arginase-1-dependent mechanism

We have shown that the expression of human papillomavirus type 16 E7 (HPV16.E7) protein within epithelial cells results in local immune suppression and a weak and ineffective immune response to E7 similar to that occuring in HPV-associated premalignancy and cancers. However, a robust acute inflammatory stimulus can overcome this to enable immune elimination of HPV16.E7-transformed epithelial cells. 2,4-Dinitrochlorobenzene (DNCB) can elicit acute inflammation and it has been shown to initiate the regression of HPV-associated genital warts. Although the clinical use of DNCB is discouraged owing to its mutagenic potential, understanding how DNCB-induced acute inflammation alters local HPV16.E7-mediated immune suppression might lead to better treatments. Here, we show that topical DNCB application to skin expressing HPV16.E7 as a transgene induces a hyperinflammatory response, which is not seen in nontransgenic control animals. The E7-associated inflammatory response is characterized by enhanced expression of Th2 cytokines and increased infiltration of CD11b(+)Gr1(int)F4/80(+)Ly6C(hi)Ly6G(low) myeloid cells, producing arginase-1. Inhibition of arginase with an arginase-specific inhibitor, N(omega)-hydroxy-nor-L-arginine, ameliorates the DNCB-induced inflammatory response. Our results demonstrate that HPV16.E7 protein enhances DNCB-associated production of arginase-1 by myeloid cells and consequent inflammatory cellular infiltration of skin.

CCR2 deficiency promotes exacerbated chronic erosive neutrophil-dominated chikungunya virus arthritis

Chikungunya virus (CHIKV) is a member of a globally distributed group of arthritogenic alphaviruses that cause weeks to months of debilitating polyarthritis/arthralgia, which is often poorly managed with current treatments. Arthritic disease is usually characterized by high levels of the chemokine CCL2 and a prodigious monocyte/macrophage infiltrate. Several inhibitors of CCL2 and its receptor CCR2 are in development and may find application for treatment of certain inflammatory conditions, including autoimmune and viral arthritides. Here we used CCR2(-/-) mice to determine the effect of CCR2 deficiency on CHIKV infection and arthritis. Although there were no significant changes in viral load or RNA persistence and only marginal changes in antiviral immunity, arthritic disease was substantially increased and prolonged in CCR2(-/-) mice compared to wild-type mice. The monocyte/macrophage infiltrate was replaced in CCR2(-/-) mice by a severe neutrophil (followed by an eosinophil) infiltrate and was associated with changes in the expression levels of multiple inflammatory mediators (including CXCL1, CXCL2, granulocyte colony-stimulating factor [G-CSF], interleukin-1β [IL-1β], and IL-10). The loss of anti-inflammatory macrophages and their activities (e.g., efferocytosis) was also implicated in exacerbated inflammation. Clear evidence of cartilage damage was also seen in CHIKV-infected CCR2(-/-) mice, a feature not normally associated with alphaviral arthritides. Although recruitment of CCR2(+) monocytes/macrophages can contribute to inflammation, it also appears to be critical for preventing excessive pathology and resolving inflammation following alphavirus infection. Caution might thus be warranted when considering therapeutic targeting of CCR2/CCL2 for the treatment of alphaviral arthritides.

IMPORTANCE

Here we describe the first analysis of viral arthritis in mice deficient for the chemokine receptor CCR2. CCR2 is thought to be central to the monocyte/macrophage-dominated inflammatory arthritic infiltrates seen after infection with arthritogenic alphaviruses such as chikungunya virus. Surprisingly, the viral arthritis caused by chikungunya virus in CCR2-deficient mice was more severe, prolonged, and erosive and was neutrophil dominated, with viral replication and persistence not being significantly affected. Monocytes/macrophages recruited by CCL2 thus also appear to be important for both preventing even worse pathology mediated by neutrophils and promoting resolution of inflammation. Caution might thus be warranted when considering the use of therapeutic agents that target CCR2/CCL2 or inflammatory monocytes/macrophages for the treatment of alphaviral (and perhaps other viral) arthritides. Individuals with diminished CCR2 responses (due to drug treatment or other reasons) may also be at risk of exacerbated arthritic disease following alphaviral infection.

Attenuating mutations in nsP1 reveal tissue-specific mechanisms for control of Ross River virus infection

Ross River virus (RRV) is one of a group of mosquito-transmitted alphaviruses that cause debilitating, and often chronic, musculoskeletal disease in humans. Previously, we reported that replacement of the nonstructural protein 1 (nsP1) gene of the mouse-virulent RRV strain T48 with that from the mouse-avirulent strain DC5692 generated a virus that was attenuated in a mouse model of disease. Here we find that the six nsP1 nonsynonymous nucleotide differences between strains T48 and DC5692 are determinants of RRV virulence, and we identify two nonsynonymous nucleotide changes as sufficient for the attenuated phenotype. RRV T48 carrying the six nonsynonymous DC5692 nucleotide differences (RRV-T48-nsP1(6M)) was attenuated in both wild-type and Rag1(-/-) mice. Despite the attenuated phenotype, RRV T48 and RRV-T48-nsP1(6M) loads in tissues of wild-type and Rag1(-/-) mice were indistinguishable from 1 to 3 days postinoculation. RRV-T48-nsP1(6M) loads in skeletal muscle tissue, but not in other tissues, decreased dramatically by 5 days postinoculation in both wild-type and Rag1(-/-) mice, suggesting that the RRV-T48-nsP1(6M) mutant is more sensitive to innate antiviral effectors than RRV T48 in a tissue-specific manner. In vitro, we found that the attenuating mutations in nsP1 conferred enhanced sensitivity to type I interferon. In agreement with these findings, RRV T48 and RRV-T48-nsP1(6M) loads were similar in mice deficient in the type I interferon receptor. Our findings suggest that the type I IFN response controls RRV infection in a tissue-specific manner and that specific amino acid changes in nsP1 are determinants of RRV virulence by regulating the sensitivity of RRV to interferon.

IMPORTANCE

Arthritogenic alphaviruses, including Ross River virus (RRV), infect humans and cause debilitating pain and inflammation of the musculoskeletal system. In this study, we identified coding changes in the RRV nsP1 gene that control the virulence of RRV and its sensitivity to the antiviral type I interferon response, a major component of antiviral defense in mammals. Furthermore, our studies revealed that the effects of these attenuating mutations are tissue specific. These findings suggest that these mutations in nsP1 influence the sensitivity of RRV to type I interferon only in specific host tissues. The new knowledge gained from these studies contributes to our understanding of host responses that control alphavirus infection and viral determinants that counteract these responses.

IL-13Rα1 is a surface marker for M2 macrophages influencing their differentiation and function

In this study, we examined the role IL-13 receptor alpha 1 (IL-13Rα1) plays in macrophage differentiation and function. The findings indicate that IL-13Rα1 is expressed on the M2 but not on the M1 subset of macrophages and specifically heterodimerizes with the IL-4Rα chain to form a type II receptor, which controls the differentiation and function of these cells. Indeed, BM cells from IL-13Rα1(+/+) and IL-13Rα1(-/-) mice yield equivalent numbers of macrophages when cultured under M2 polarizing conditions. However, IL-13Rα1(-/-) BM cells yield a much higher number of macrophages than IL-13Rα1(+/+) BM cells when the differentiation is carried out under M1-polarizing conditions. Further analyses indicated that macrophages that express IL-13Rα1 also display surface markers associated with an M2 phenotype. In addition, the IL-13Rα1(+) macrophages were highly efficient in phagocytizing zymosan bioparticles both in vitro and in vivo, and supported differentiation of naïve T cells to a Th2 phenotype. Finally, when stimulated by IL-13, a cytokine that uses the heteroreceptor, the cells were able to phosphorylate STAT6 efficiently. These previously unrecognized findings indicate that IL-13Rα1 serves as a marker for M2 macrophages and the resulting heteroreceptor influences both their differentiation and function.

Chronic joint disease caused by persistent Chikungunya virus infection is controlled by the adaptive immune response

Chikungunya virus (CHIKV) is a reemerging mosquito-borne pathogen that causes incapacitating disease in humans characterized by intense joint pain that can persist for weeks, months, or even years. Although there is some evidence of persistent CHIKV infection in humans suffering from chronic rheumatologic disease symptoms, little is known about chronic disease pathogenesis, and no specific therapies exist for acute or chronic CHIKV disease. To investigate mechanisms of chronic CHIKV-induced disease, we utilized a mouse model and defined the duration of CHIKV infection in tissues and the associated histopathological changes. Although CHIKV RNA was readily detectable in a variety of tissues very early after infection, CHIKV RNA persisted specifically in joint-associated tissues for at least 16 weeks. Inoculation of Rag1(-/-) mice, which lack T and B cells, resulted in higher viral levels in a variety of tissues, suggesting that adaptive immunity controls the tissue specificity and persistence of CHIKV infection. The presence of CHIKV RNA in tissues of wild-type and Rag1(-/-) mice was associated with histopathological evidence of synovitis, arthritis, and tendonitis; thus, CHIKV-induced persistent arthritis is not mediated primarily by adaptive immune responses. Finally, we show that prophylactic administration of CHIKV-specific monoclonal antibodies prevented the establishment of CHIKV persistence, whereas therapeutic administration had tissue-specific efficacy. These findings suggest that chronic musculoskeletal tissue pathology is caused by persistent CHIKV infection and controlled by adaptive immune responses. Our results have significant implications for the development of strategies to mitigate the disease burden associated with CHIKV infection in humans.

Retnla down-regulation and IL-13-rich environment correlate with inflammation severity in experimental actinomycetoma by Nocardia brasiliensis

Nocardia brasiliensis (Nb) is a facultative intracellular pathogen that may cause actinomycetoma when immune response is unable to control the pathogenic invasion. We used comparative real-time PCR to evaluate the expression level of molecules indicative of either classical or alternative activation of macrophages, as well as of cytokines involved in macrophage polarization, during the experimental infection in BALB/c mice. We found induction or increased expression of the pro-inflammatory markers csf2/GM-CSF, interferon-gamma, and nos2/iNOS. The expression of Ym1 and IL-13, which are usually related with alternative activation of macrophage, was also increased. However, retnla/FIZZ1 expression decreased sharply during the infection. We concluded that Nb infection induces both a pro-inflammatory and anti-inflammatory environment, in which there is a strong inverse correlation between IL-13 and retnla expression.

A tyrosine-to-histidine switch at position 18 of the Ross River virus E2 glycoprotein is a determinant of virus fitness in disparate hosts

Arthritogenic alphaviruses are human pathogens maintained in nature through alternating replication in vertebrates and mosquitoes. Using chimeric viruses, we previously reported that replacement of the PE2 coding region of the T48 strain of Ross River virus (RRV-T48) with that from the attenuated DC5692 strain, which differ by 7 amino acids, resulted in an attenuated disease phenotype in a mouse model of RRV-induced rheumatic disease. Here, we demonstrate that introduction of one of these amino acid differences, a tyrosine (Y)-to-histidine (H) change at position 18 of the E2 glycoprotein (E2 Y18H), into the RRV-T48 genetic background was sufficient to generate a virus that caused dramatically less severe musculoskeletal disease in mice. The attenuated phenotype of RRV-T48 E2 Y18H was associated with reduced viral loads in musculoskeletal tissues, reduced viremia, and less efficient virus spread. Consistent with these findings, RRV-T48 E2 Y18H replicated less well in mammalian cells in vitro due to significantly reduced PFU released per infected cell. In contrast, RRV-T48 E2 Y18H replicated more efficiently than RRV-T48 in C6/36 mosquito cells. Competition studies confirmed that RRV-T48 E2 Y18H had a fitness advantage in mosquito cells and a fitness disadvantage in mammalian cells. Interestingly, all sequenced Ross River viruses encode either a tyrosine or a histidine at E2 position 18, and this holds true for other alphaviruses in the Semliki Forest antigenic complex. Taken together, these findings suggest that a tyrosine-to-histidine switch at E2 position 18 functions as a regulator of RRV fitness in vertebrate and invertebrate cells.

Transgenic CCL2 expression in the central nervous system results in a dysregulated immune response and enhanced lethality after coronavirus infection

Chemokine (C-C motif) ligand 2 (CCL2), a chemoattractant for macrophages, T cells, and cells expressing CCR2, is upregulated during acute and chronic inflammation. CCL2 has been implicated in both proinflammatory and anti-inflammatory responses and has been suggested as a target for therapy in some inflammatory disorders. To examine the role of CCL2 during virus infection, we infected mice transgenically expressing CCL2 in the central nervous system (CCL2 Tg) with an attenuated neurotropic coronavirus (rJ2.2 strain of mouse hepatitis virus). Infection of wild-type mice with rJ2.2 results in mild acute encephalitis, followed by a nonlethal, chronic demyelinating disease. Proinflammatory innate and adaptive immune responses mediate virus clearance. In marked contrast, CCL2 Tg mice infected with rJ2.2 ineffectively cleared virus and rapidly succumbed to the infection. CCL2 Tg mice mounted a dysregulated immune response, characterized by augmented accumulation of regulatory Foxp3(+)CD4(+) T cells and of nitric-oxide- and YM-1-expressing macrophages and microglia, suggestive of mixed M1/M2 macrophage activation. Further, macrophages from infected CCL2 Tg brains relative to non-Tg controls were less activated/mature, expressing lower levels of major histocompatibility complex class II (MHC-II), CD86, and CD40. Collectively, these results show that persistent CCL2 overexpression establishes and sustains an immunological milieu that is both inflammatory and immunosuppressive and predisposes mice to a defective immune response to a minimally lethal virus.