Lack of pathogenic involvement of CCL4 and its receptor CCR5 in arthritogenic alphavirus disease

Arthritogenic alphaviruses, including chikungunya virus (CHIKV), Mayaro virus (MAYV), Ross River virus (RRV), and O'nyong nyong virus (ONNV) are emerging and reemerging viruses that cause disease characterized by fever, rash, and incapacitating joint swelling. Alphavirus infection induces robust immune responses in infected hosts, leading to the upregulation of several cytokines and chemokines, including chemokine C ligand 4 (CCL4). CCL4 is a chemoattractant for immune cells such as T cells, natural killer cells, monocytes/macrophages, and dendritic cells, recruiting these cells to the site of infection, stimulating the release of proinflammatory mediators, and inducing T cell differentiation. CCL4 has been found at high levels in both the acute and chronic phases of chikungunya disease; however, the role of CCL4 in arthritogenic alphavirus disease development remains unexplored. Here, we tested the effect of CCL4 on MAYV infection in mice through antibody depletion and treatment with recombinant mouse CCL4. We observed no differences in mice depleted of CCL4 or treated with recombinant CCL4 in terms of disease progression such as weight loss and footpad swelling or the development of viremia. CCL4 uses the G protein-coupled receptor C-C chemokine receptor type 5 (CCR5). To determine whether CCR5 deficiency would alter disease outcomes or virus replication in mice, we inoculated CCR5 knockout (CCR5^-/-) mice with MAYV and observed no effect on disease development and immune cell profile of blood and footpads between CCR5^-/- and wild type mice. These studies failed to identify a clear role for CCL4 or its receptor CCR5 in MAYV infection.