The agglutinating and immunofluorescent activities of antileptospiral antibodies of human sera and of immunoglobulins M and G.

Microagglutinating and immunofluorescent activities of sera of nine patients with clinically diagnosed leptospirosis were investigated. L. grippotyphosa was found in seven patients, L. sejroe in one and L. icterohaemorrhagiae in one patient. The agglutinating activities of IgM approximated the activities of the whole sera. In five patients the agglutinating activities were found in IgG; in four of them two to three months after the onset of the disease, in one patient a month after its onset. In one patient only the activity of IgG reached the activity of IgM after six months. Immunofluorescent activity was found in IgG in eight patients two to five weeks after the onset of the disease. In seven of these patients the activity of IgG reached or exceeded the activity of IgM three to ten weeks after the onset of the disease. IFAT was found to be poorly specific because of high heterologous titres. In 5 out of 7 patients with L. grippotyphosa, heterologous IFAT titres were reduced or eliminated by carrying out the reaction with isolated IgM and IgG. However, in patients with L. icterohaemorrhagiae and with L. sejroe heterologous IFAT activity persisted in both IgM and IgG. The study points out the possibility of differentiating an early stage of the infection from convalescence.