Cellular Immunity in COVID 19 Convalescents with PCR Confirmed Infection but with Undetectable SARS CoV 2 Specific IgG.
We investigated immune responses against severe acute respiratory syndrome coronavirus 2 (SARS CoV 2) among a group of convalescent, potential blood donors in Germany who had PCR confirmed SARS CoV 2 infection. Sixty days after onset of symptoms, 13/78 (17% study participants had borderline or negative results to an ELISA detecting IgG against the S1 protein of SARS CoV 2. We analyzed participants with PCR confirmed infection who had strong antibody responses (ratio >3) as positive controls and participants without symptoms of SARS CoV 2 infection and without household contact with infected patients as negative controls. Using interferon g ELISpot, we observed that 78% of PCR positive volunteers with undetectable antibodies showed T cell immunity against SARS CoV 2. We observed a similar frequency (80% of T cell immunity in convalescent donors with strong antibody responses but did not detect immunity in negative controls. We concluded that, in convalescent patients with undetectable SARS CoV 2 IgG, immunity may be mediated through T cells.
Emerging infectious diseases