Antibacterial peptides are secreted into the midgut lumen to provide antibacterial midgut defense in the soft tick, Ornithodoros moubata (Acari: Argasidae)

Antibacterial peptide defensin isoform A was previously isolated from the midgut contents of Ornithodoros moubata blood-fed females. However, not only defensin A, but also three other defensin isoforms showed gene expression in the midgut, suggesting the possibility that these antibacterial peptides are secreted into the midgut lumen. To further understand tick immune mechanisms, the involvement of antibacterial peptides in midgut defense was investigated. Three antibacterial peptides with molecular masses near defensin isoforms B, C and D were detected in the midgut contents of blood-fed females. Enzyme-linked immunosorbent assay analysis revealed that the antibacterial peptides in the midgut contents cross-reacted with defensin A antibodies and increased as a response to blood feeding. Simultaneously, the antibacterial activity of the midgut contents was enhanced by blood feeding. Secretion of antibacterial peptides into the midgut lumen and an increase in the peptide concentration following blood feeding was also confirmed. These findings further support the hypothesis that antibacterial peptides play an important role in the midgut defense of ticks.