Phlebotomine insects harbor bacterial,
viral and parasitic pathogens that can cause diseases of public health
importance. Lutzomyia longipalpis is the main vector of visceral
leishmaniasis in the New World. Insects can mount a powerful innate immune
response to pathogens. Defensin peptides take part in this response and are
known to be active against Gram-positive and Gram-negative bacteria, and some
parasites. We studied the expression of a defensin gene from Lutzomyia
longipalpis to understand its role in sand fly immune response.
sequenced and evaluated the expression of a L. longipalpis defensin gene by
semi-quantitative RT-PCR. The gene sequence was compared to other vectors
defensins and expression was determined along developmental stages and after
exposure of adult female L. longipalpis to bacteria and Leishmania.
analysis showed that the L. longipalpis defensin is closely related to a
defensin from the Old World sand fly Phlebotomus duboscqi. Expression was
high in late L4 larvae and pupae in comparison to early larval stages and
newly emerged flies. Defensin expression was modulated by oral infection with
bacteria. The Gram-positive Micrococcus luteus induced early high defensin expression,
whilst the Gram-negative entomopathogenic Serratia marcescens induced a later
response. Bacterial injection also induced defensin expression in adult
insects. Female sand flies infected orally with Leishmania mexicana showed no
significant difference in defensin expression compared to blood fed insects
apart from a lower defensin expression 5 days post Leishmania infection. When
Leishmania was introduced into the hemolymph by injection there was no
induction of defensin expression until 72 h later.
suggest that L. longipalpis modulates defensin expression upon bacterial and
Leishmania infection, with patterns of expression that are distinct among
bacterial species and routes of infection.