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.