Characterization of ixodid tick salivary-gland gene products, using recombinant DNA technology

Ticks secrete an array of lesion-maintenance factors into the host via the salivary glands while feeding, some of which elicit an immune response by the host that adversely affects the ability of the tick to feed and reproduce. Our approach to characterizing these factors has been to make expression libraries from mRNA of salivary glands (from unfed and 3-day-feeding Amblyomma americanum females) which will serve as sources of the genes (clones) that code for them. Thus far, we have detected 10 positive clones in primary screens using polyspecific antiserum from rabbits hyperimmunized to 3-day-feeding tick salivary glands. We also report making a cDNA library from whole unfed females, and a genomic library from whole unfed ticks, which will serve as additional sources of genetic information for characterizing salivary-gland secretory products. Immunoblots of salivary glands from A. americanum females feeding for various intervals (unfed, and 12, 48, 72, and 96 h) revealed the presence of several prominent polypeptides (90 & 45 kDa) when probed with the same rabbit antiserum that was used to screen the expression library. Ixodes dammini had several immunogens in common with A. americanum at 96 h (90, 45, 43 and 23 kDa). We plan to use monospecific antiserum raised to antigens detected in our immunoblots (e.g. 90 kDa) to further screen the expression libraries, in addition to using the polyspecific antiserum already in hand. We discuss the future use of the salivary-gland genes for characterizing secretory products which facilitate attachment to the host (cement) and maintain the lesion during the lengthy feeding interval.