Maxadilan is a small ( approximately 7 kDa)
protein found in the saliva of sand fly species in the Lutzomyia longipalpis complex, vectors of the parasite causing
visceral leishmaniasis, Leishmania chagasi. It is a potent
vasodilator and also has immunomodulatory affects.
Maxadilan recovered from different sibling species of the Lu. longipalpis complex differ in
amino acid content by as much as 23%, however all variants possess equivalent vasodilatory activity. Therefore, the dramatic differences in vasodilatory activity of the saliva from different sibling species is probably due to differences in the amounts of
maxadilan in their saliva. This is significant because it has been suggested that
maxadilan may influence the pathogenesis of leishmanial
infections. In this study we measured the amount of
maxadilan messenger RNA (
mRNA) per pair of salivary glands from individual sand flies by quantitative reverse transcription polymerase chain reaction (RT-PCR) using a competitive method. We report a method using the gene of interest, in this case
maxadilan, amplified by the PCR from genomic
DNA, as a competitor in the quantitative RT-PCR, taking advantage of differences in the size of these products due to the presence of an intron. Significant differences in amounts of
maxadilan mRNA among colonies from Central and South America are described. We found a strong correlation between the amount of
maxadilan mRNA detected in salivary glands of different Lu. longipalpis sibling species and previously described differences in the size of
erythemas produced by the
bite of these species. Therefore, variation in the amount of
mRNA suggests that differences in the vasodilatory properties of saliva among the different sibling species are the result of differences in the amount of
maxadilan present in the saliva and not differences in the potency of
maxadilan peptide variants. The geographical distribution of species with high or low levels of
maxadilan gene expression are concordant with the distribution of atypical
cutaneous leishmaniasis resulting from
infection with Le. chagasi, lending credence to earlier suggestions that
maxadilan may be involved with visceralization of this parasite.