Thus, while increased IgG and IgA binding to citrulline- and homocitrulline-containing IgG peptides is generally specific for rheumatoid arthritis (Figures 1, 3), there is some reactivity, especially for IgA and homocitrulline-containing IgG epitopes, in some post-COVID-19 participants (Table 1, Figure 4). The gene discussed is CD79A; the disease is rheumatoid arthritis.