Insulin-like Growth Factor (IGF)-I affects parasite growth and host cell migration in experimental cutaneous leishmaniasis

While the control or progression of leishmaniasis depends on host immune responses, the initial inflammatory process represents a key event. This process involves the participation of several cytokines and growth factors induced during inflammation as well as factors already present at the site of infection such as insulin‐like growth factor (IGF)‐I. We have previously demonstrated a potential role for IGF‐I in experimental cutaneous leishmaniasis based on the significant increase in lesion size seen in mice injected with Leishmania promastigotes preactivated with IGF‐I. In the present study we show that preactivation of Leishmania (Leishmania) amazonensis promastigotes with IGF‐I induces an increase in the actual number of parasites at the lesion site from seven days postinfection, in addition to a more intense inflammatory infiltrate. There was a higher numerical density of polymorphonuclear neutrophils from 3 to 24 h, and of mononuclear cells from 48 h of infection onward. A higher density of polymorphonuclear neutrophils and mononuclear cells harboring parasites was also observed. The most important observation, however, was that more parasites per cell were present, revealing that IGF‐I appears to favour parasite growth within the macrophages. These results strongly suggest an important role for IGF‐I in the development of cutaneous leishmaniasis, where it influences both the inflammatory process and parasite growth.