Immunity in Rhodnius prolixus: trypanosomatid-vector interactions.

Many insects respond to a bacterial infection with the stimulation of distinct cellular and humoral defense system, that cooperate in a more or less integrated way to decrease the chance of microorganisms becoming pathogens. Cellular reactions include phagocytosis, nodule formation, and in some cases encapsulation and other factors related to immune system as prophenoloxidase (proPO) system, lectin, lysozyme and induced peptides such cecropin, attacin and other factors (Ratcliffe & Rowley 1979, Dunn 1986, Boman & Hultmark 1987). Feder et al. (1997) demonstrated, when Rhodnius prolixus was challenged with Enterobater cloacae, the importance of the effects of diet components on the immune reactivity. For example, plasma diet induced immune depression. Ecdysone therapy counteracted the immune depression in Rhodnius larvae fed on plasma diet alone (Feder et al. 1997). In spite of the extensive research conducted over the last few years on the molecular bases of these responses, the regulation on the blood sucking insect defense reaction against parasite remains relatively poor understood. Many trypanosomatides develop their cycles in the hemocel and/ or digestive tract of the insect vector. While in R. prolixus the development of Trypanosoma cruzi (causative agent of Chagas diesease) is confined to the gut lumen, T. rangeli develops in the gut but clearly invades the hemolymph and survives free in the blood or inside the hemocytes (Brener 1972, D’Alessandro 1976, Garcia & Azambuja 1991). The importance of the vector immune system as an essential component of the parasite-insect vector relationship has recently been recognized (Molyneux et al. 1986, Kaaya 1989, Ingram & Molyneux 1991, Mello et al. 1995). In this paper we present findings to support the hypothesis that the vector immune system may have a role in the trypanosomatid-triatomine interaction.