Early anti-SARS-CoV-2 immunoglobulin G response may be associated with disease severity in patients with COVID-19.

Maeda, Tadashi; Kashiwagi, Katsuhito; Yoshizawa, Sadako; Sato, Takahiro; Aoki, Kotaro; Ishii, Yoshikazu; Tateda, Kazuhiro

Most COVID-19 patients are mild or asymptomatic; a substantial minority of patients develop severe or critical disease. There are many reports on potential risk factors for severe disease, but few reports have reported a relationship between antibody titer and severity in Japan. Antibody-dependent enhancement (ADE) is one such factor theorized to affect the worsening of disease. We have been evaluating IgG responses in COVID-19 patients at our tertiary hospital. A measure of interest is the IgG index, we assigned 1.4 as the cutoff value for a positive result according to the manufacturer indication and observed that patients could be categorised into two distinct groups: early elevation of IgG and late elevation of IgG (IgG elevated in the first 7 days ± 2 days or more than 10 days after symptom onset). We defined the former as early-IgG responders (N=7) and the latter as late-IgG responders (N=14) and compared them. C-reactive protein and D-dimer levels were significantly higher on admission (HD 0) and the respiratory rate was higher, lymphocytes were lower significantly on day 7 of hospitalization (HD 7) in the early-IgG responders. These results might implicate that early production of anti-severe acute respiratory syndrome coronavirus 2 IgG may be associated with clinical indicator for severity.