The adulticide effect of a combination of doxycycline and ivermectin in Dirofilaria immitis-experimentally infected dogs is associated with reduction in local T regulatory cell populations.

In a previous study, dogs experimentally infected with Dirofilaria immitis were treated with either ivermectin or doxycycline or a combination of both. The adulticide effect was significantly higher in the dogs treated with both drugs and was similar to that observed in dogs treated with melarsomine hydrochloride. In the present study, lung tissue samples from these dogs were evaluated for the presence of T regulatory (Foxp3+) cells by immunohistochemistry. Cells were enumerated for each dog in the four groups and compared with untreated controls. There was a significantly lower number of Treg cells in those dogs treated with a combination of both drugs when compared either to the control group or to the other groups treated with either drug alone or with melarsomine. These results suggest that successful adulticide effects of doxycycline and ivermectin are associated with a decrease in immune regulation towards the parasite.