Alphaviruses, including Chikungunya virus (CHIKV), produce a transient illness in humans, but severe forms leading to chronic incapacitating arthralgia/arthritis have been reported by mechanisms largely ill-characterized. The pathogenesis of CHIKV was addressed in a prospective cohort study of 49 hospitalized patients from Reunion Island subsequently categorized into two distinct groups at 12 mo postinfection. Comprehensive analyses of the clinical and immunological parameters throughout the disease course were analyzed in either the “recovered” or the “chronic” groups to identify prognostic markers of arthritis-like pathology after CHIKV disease. We found that the chronic group consisted mainly of more elderly patients (>60 y) and with much higher viral loads (up to 10¹⁰ viruses per milliliter of blood) during the acute phase. Remarkably, a rapid innate immune antiviral response was demonstrated by robust dendritic/NK/CD4/CD8 cell activation and accompanied by a rather weak Th1/Th2 cytokine response in both groups. Interestingly, the antiviral immune response witnessed by high levels of IFN-α mRNA in PBMCs and circulating IL-12 persisted for months only in the chronic group. CHIKV (RNA and proteins) was found in perivascular synovial macrophages in one chronic patient 18 mo postinfection surrounded by infiltrating NK and T cells (CD4⁺⁺ but rare cytotoxic CD8). Fibroblast hyperplasia, strong angiogenesis, tissue lesions given the high levels of matrix metalloproteinase 2, and acute cell death [high cleaved poly(ADP-ribose) polymerase staining] were observed in the injured synovial tissue. These observed cellular and molecular events may contribute to chronic arthralgia/arthritis targeted by methotrexate used empirically for effective treatment but with immunosuppressive function in a context of viral persistence.

Chikungunya virus (CHIKV) surprised medical workers by a massive outbreak in the Indian Ocean region, reaching Europe in 2007, with exceptional pathologies in infants and elderly patients. Although CHIKV was recently shown to persist in myo‐blasts, monocytes, and macrophages, we argued that robust antiviral mechanisms, including apoptosis, are essential to ward off the virus. Herein, we tested the capacity of CHIKVto mobilize the apoptotic machinery in HeLa cells as well as primary fibroblasts, making use of several inhibitors of caspases, cell blebbing, and engulfment of the apoptotic blebs by neighboring cells. CHIKV triggered apoptosis through intrinsic and extrinsic pathways. Bystander apoptosis was also evidenced in neighboring cells in a caspase‐8‐dependent manner. Remarkably, by hiding in apoptotic blebs, CHIKV was able to infect neighboring cells. In HeLa cells, these events were inhibited specifically by zVAD‐fmk and DEVD‐cho (caspase inhibitors), blebbistatin, Y‐27632 (ROCK inhibitor), and genistein, annexin V, and cytochalasin B (inhibitors of blebbing and engulf‐ment). These CHIKV‐apoptotic blebs were also capable of infecting macrophages (primary cultures, MM6‐ and THP1‐PMA differentiated cells) otherwise refractory to infection by CHIKV alone. Remarkably, viral replication in macrophages did not yield a proinflammatory response. We describe a novel infectious mechanism by which CHIKV invades host cells and escapes the host response.—Krejbich‐Trotot, P., Denizot, M., Hoarau, J.‐J., Jaffar‐Bandjee, M.‐C., Das, T., Gasque, P. Chikun‐gunya virus mobilizes the apoptotic machinery to invade host cell defenses. FASEB J. 25, 314–325 (2011). www.fasebj.org

Background: Chikungunya Virus (ChikV) surprised by a massive re-emerging outbreak in Indian Ocean in 2006, reaching Europe in 2007 and exhibited exceptional severe physiopathology in infants and elderly patients. In this context, it is important to analyze the innate immune host responses triggered against ChikV. Autophagy has been shown to be an important component of the innate immune response and is involved in host defense elimination of different pathogens. However, the autophagic process was recently observed to be hijacked by virus for their own replication. Here we provide the first evidence that hallmarks of autophagy are specifically found in HEK.293 infected cells and are involved in ChikV replication. Methods: To test the capacity of ChikV to mobilize the autophagic machinery, we performed fluorescence microscopy experiments on HEK.GFP.LC3 stable cells, and followed the LC3 distribution during the time course of ChikV infection. To confirm this, we performed electron microscopy on HEK.293 infected cells. To test the effect of ChikV-induced-autophagy on viral replication, we blocked the autophagic process, either by pharmacological (3-MA) or genetic inhibition (siRNA against the transcript of Beclin 1, an autophagic protein), and analyzed the percentage of infected cells and the viral RNA load released in the supernatant. Moreover, the effect of induction of autophagy by Rapamycin on viral replication was tested. Results: The increasing number of GFP-LC3 positive cells with a punctate staining together with the enhanced number of GFP-LC3 dots per cell showed that ChikV triggered an autophagic process in HEK.293 infected cells. Those results were confirmed by electron microscopy analysis since numerous membrane-bound vacuoles characteristic of autophagosomes were observed in infected cells. Moreover, we found that inhibition of autophagy, either by biochemical reagent and RNA interference, dramatically decreases ChikV replication. Conclusions: Taken together, our results suggest that autophagy may play a promoting role in ChikV replication. Investigating in details the relationship between autophagy and viral replication will greatly improve our knowledge of the pathogenesis of ChikV and provide insight for the design of candidate antiviral therapeutics.