Dirofilaria immitis: cell-mediated and humoral immune responses in experimentally-infected dogs.

Four dogs were experimentally infected with 30 Dirofilaria immitis infective larvae, four dogs received two such infections and four dogs served as uninfected controls. A partially-purified D. immitis antigen was used in an indirect hemagglutination assay to determine anti-D. immitis antibody titers. Anti-D. immitis antibody was first detected in infected dogs 4 weeks after infection. Titers were highest 2 weeks after the appearance of microfilariae and diminished to low levels thereafter in the single infection group. Antibody levels in the double infection group decreased similarly but were demonstrable throughout the study. Antibody titers were significantly higher in the infected dogs, but there were no differences in titers between single and double infection groups.The responses of peripheral lymphocytes to phytohemagglutinin P and pokeweed mitogen were significantly depressed in infected dogs. Peripheral blood lymphocyte transformation could not be induced with D. immitis antigens. Differences between groups in T-cell function were not demonstrated by total hemagglutinating antibody or 2-mercaptoethanol labile hemagglutinating antibody following immunization with sheep erythrocytes.