The synovial mast cell remains an important component during RA joint destruction by the exocytosis of intracellular granules containing inflammatory mediators. Currently, mast cell activation through FccRs by high levels of circulating IgG antibodies is hypothesized to contribute to the pathological destruction of synovium in RA [44] [45] [46] . In addition, antibody immune complex formation within the joint stabilizing inflammatory mediators, such as chemokines and complement proteins, is another possible low IgG level group (L) and a high IgG level group (H). Cytokine Bead Array analysis of the serum samples showed a significant difference in CXCL9, CXCL10 and IL-6 between patients with high and low IgG levels at the 6-month time point. Twelve-month follow-up CHIKV patient samples showed a significant difference in CXCL9 and IL-10 between low (1) and high (2) IgG groups. A Mann-Whitney U test was used to determine significance among the IgG groups. The cross symbol indicates a p-value less than 0.05. doi:10.1371/journal.pntd.0001279.g005