Vaccination against encapsulated bacteria in hereditary C2 deficiency results in antibody response and opsonization due to antibody-dependent complement activation

► We have demonstrated that vaccination in C2 deficiency gives an antibody response. ► The antibody response varies from low to normal in relation to antigen and person. ► Specific antibodies induce opsonization with C3 fragments in C2 deficiency. ► The antibody-dependent activation of C3 is by a C1q-dependent C2 bypass mechanism. ► Our findings suggest that vaccination results in increased bacterial phagocytosis.