Involvement of antibacterial peptide defensin in tick midgut defense.

Animals are constantly threatened by pathogenic microorganisms and have developed cellular and humoral immune responses to combat these infections. Invertebrates possess only an innate non-specific immune response. Antimicrobial substances are major components of innate immunity not only in invertebrates but also in vertebrates. Despite the importance of ticks as vectors of disease very little is known about their immune system. Our recent studies have revealed that four defensin isoforms are present in Ornithodoros moubata. These four isoforms are constitutively expressed in the midgut and up-regulated in response to blood feeding. Moreover, a mature peptide of defensin isoform A has been isolated from the tick midgut lumen. These findings indicate Ornithodoros defensins are involved in tick midgut defense against potentially harmful invasive microbes.