Sibling species in the Lutzomyia longipalpis complex differ in levels of mRNA expression for the salivary peptide, maxadilan

Maxadilan is a small (approximate to 7 kDa) protein found in the saliva of sand fly species in the Lutzomyia longipalpis complex, vectors of the paras ite causing visceral leishmaniasis, Leishmania chagasi. It is a potent vaso dilator and also has immunomodulatory affects. Maxadilan recovered from dif ferent sibling species of the Lu, longipalpis complex differ in amino acid content by as much as 23%, however all variants possess equivalent vasodila tory activity. Therefore, the dramatic differences in vasodilatory activity of the saliva from different sibling species is probably due to difference s in the amounts of maxadilan in their saliva. This is significant because it has been suggested that maxadilan may influence the pathogenesis of leis hmanial infections. In this study we measured the amount of maxadilan messe nger RNA (mRNA) per pair of salivary glands from individual sand flies by q uantitative reverse transcription polymerase chain reaction (RT-PCR) using a competitive method. We report a method using the gene of interest, in thi s 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 th ese products due to the presence of an intron. Significant differences in a mounts of maxadilan mRNA among colonies from Central and South America are described. We found a strong correlation between the amount of maxadilan mR NA detected in salivary glands of different Lu, longipalpis sibling species and previously described differences in the sire of erythemas produced by the bite of these species. Therefore, variation in the amount of mRNA sugge sts that differences in the vasodilatory properties of saliva among the dif ferent sibling species are the result of differences in the amount of maxad ilan 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 o f atypical cutaneous leishmaniasis resulting from infection with Le. chagas i, tending credence to earlier suggestions that maxadilan may be involved w ith visceralization of this parasite.