Footpad reaction induced by Neospora caninum tachyzoite extract in infected BALB/c mice

Little information is available regarding a delayed type hypersensitivity (DTH) reaction in neosporosis. In this study, we examined the elicitation of a DTH reaction in mice infected with Neospora caninum by inoculation of the footpad with tachyzoite antigens. The footpads of BALB/c mice infected with N. caninum and those of non-infected were injected with either the tachyzoite extract, or paraformaldehyde-fixed tachyzoites. In mice inoculated with N. caninum antigens on day 7 p.i. swelling peaked at 6 h after injection of the tachyzoite extract. In mice inoculated on days 14, 28 and 56, swelling was observed between 6 and 72 h afterwards. Mice immunized with the tachyzoite extract plus adjuvant showed peak footpad swelling at 6 h post injection, and the swelling had decreased at 24 h or later. In contrast, mice injected before infection showed no specific swelling. In sections of footpads injected with the tachyzoite extract, exudate had accumulated at 6 h post injection and clusters of infiltrated lymphocytes were observed at 48 h post injection. In mice administered anti-CD4+ cell monoclonal antibodies swelling had decreased at 24 h post injection of the extract. These results indicate that mice infected with N. caninum produce a DTH reaction, which is a good indicator of the development of type 1 immune responses.