Effective humoral immunity against diphtheria and tetanus in patients with systemic lupus erythematosus or myasthenia gravis

► Diphtheria-antitoxin IgG levels do not differ between controls and SLE patients. ► Tetanus-antitoxoid IgG levels do not differ between controls and SLE or MG patients. ► Severity of SLE or MG does not influence the vaccine-induced immune response. ► First study on humoral immunity against diphtheria and tetanus in MG patients. Controversy exists about the effectiveness of vaccine-induced immune response in patients with immunoregulatory disorders. Our aim was to determine the antibody titers to diphtheria and tetanus in patients with either of two autoimmune diseases. 279 patients with SLE (205 females, aged 45.0±13.8 years), 158 patients with myasthenia gravis (MG) (101 females, aged 55±18.7 years) and 208 healthy subjects (122 females, aged 48±14.6 years) were enrolled. Serum concentrations of diphtheria-antitoxin-IgG (A-DIPHTH) and tetanus-antitoxoid-IgG (A-TET) were determined with ELISA. Equal proportions of healthy subjects, as well as patients with SLE or MG exhibited proper antibody responses and immune protection against diphtheria and tetanus. In all three test groups, serum concentration of A-DIPHTH decreased significantly (p60-years-old) subjects. There were no significant differences among the groups in the age-related changes of A-TET and A-DIPHTH except that in