Date of Award

Fall 2007

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Wayne L. Hynes

Committee Member

Roland Cooper

Committee Member

Alex Greenwood

Call Number for Print

Special Collections LD4331.B46 S42 2007


Hematophagous arthropods, such as ticks and mosquitoes, rely on their innate immune system for defense against pathogens ingested in a blood meal as well as those acquired through injury. In response to pathogen recognition, the production of antimicrobial peptides, such as defensin, is typically upregulated. Varisin, a defensin, is thought to be a key component in the immunocompetence of the hard tick D. variabilis against Borrelia burgdorferi, the causative agent of Lyme disease. To study the antimicrobial effects of varisin, recombinant varisin was expressed by both insect cells and E coli. Purification of the protein followed by enterokinase treatment yielded a protein identified by Western blotting as varisin. However, neither recombinant protein was bactericidal against M. luteus, a bacterium with known susceptibility to varisin. The lack of activity is possibly the result of varisin aggregates forming prior to their interaction with the target cell. Synthetic varisin was shown to inhibit the growth of 13 out of 14 Gram-positive bacteria and 2 out of 20 Gram-negative bacteria via well-diffusion and microtiter inhibition assays. Studies of varisin are essential to further our understanding of the innate immune response as well as providing possible insight into treatment or preventative measures for bacterial illness.


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