In this report we provide a hypothesis of how intravenous immunoglobulin (IvIg) (pooled therapeutic normal IgG) mitigates the severe disease after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The disease is caused by an overreaction of the innate immune system producing a cytokine storm and inflicting multiple organ damage. Our interpretation of IvIg therapy hinges on a recent analysis of the immune dysregulation in Covid-19 infection. Previous infections with common cold coronavirus induce suppressor memory B cells that inhibit an immune response to Covid-19. The repertoire of natural antibodies (IvIg) contains suppressing antibodies in a symmetrically balanced network structure. When this repertoire interacts with the imbalanced network in the infected patient, it can neutralize the suppression of an antibody response against Covid-19. The described scenario for IvIg in Covid-19 infection may also apply in the therapy of autoimmune diseases.