A defensin‐like gene expressed in the black‐legged tick, Ixodes scapularis

Abstract

The black-legged tick Ixodes scapularis Linnaeus (Acari: Ixodidae) is an important vector of microbial pathogens. Knowledge of the tick's innate immune response, particularly defensin and other antimicrobial peptides, is important for understanding how microbes survive in this tick. A defensin gene (slnA) from I. scapularis was obtained by reverse transcription-polymerase chain reaction (RT-PCR) using mRNA extracted from tissues of female ticks. RT-PCR indicated the gene was expressed in the midgut, haemocytes, and fat-body, although no evidence of a peptide was found. Sequencing a cloned cDNA fragment revealed a 225 bp open reading frame encoding a 74 amino acid pre-prodefensin, including the putative 38 amino acid mature peptide. Similarity between the defensin amino acid sequences of I. scapularis and Dermacentor variabilis (Say) (Acari: Ixodidae) was 62.2% for the pre-prodefensin region; for the mature defensins from these two species the similarity was 78.9%, with the six cysteine residues being located in the same relative position. PCR amplification and sequencing of chromosomal DNA suggests that slnA, along with vsnA, the defensin gene from D. variabilis, does not contain any introns. This is in contrast to the defensins described for the soft tick, Ornithodoros moubata (sensu Walton) (Acari: Argasidae). The role of defensin in the innate immune response of I. scapularis following microbial invasions is discussed.

Analysis of the Borrelia burgdorferi Cyclic-di-GMP-Binding Protein PlzA Reveals a Role in Motility and Virulence

“…Tick saliva contains bioactive molecules and a plethora of proteolytic enzymes (19,75). Whether tick-derived elements, host-derived products acquired from the tick's blood meal, or salivary gland factors (18,19,34,75,81,82) were responsible for the reduced survival of the plzA mutant in the ticks remains to be determined. We and others have shown that B. burgdorferi uses different mechanisms to survive in different hosts (ticks/mammalian).…”

The Hybrid Histidine Kinase Hk1 Is Part of a Two-Component System That Is Essential for Survival of Borrelia burgdorferi in Feeding Ixodes scapularis Ticks

“…During acquisition, spirochetes first encounter these molecules as they migrate into the feeding site, while spirochetes within flat nymphs (or larvae infected by immersion) would encounter these ligands solely within the midgut (3). The Hk1/Rrp1-directed synthesis of c-di-GMP initiates an adaptive response that enables spirochetes either to evade killing by noxious substances within midgut epithelium as feeding progresses (21,37,50,73,74) or to adjust metabolically to growth within the arthropod vector. In contrast to the Rrp2/RpoN/RpoS pathway, which is active (ON) only within feeding nymphs, the Hk1/Rrp1 TCS is essential for survival during both the larval and nymphal blood meals.…”

Rickettsia peacockii, an endosymbiont of Dermacentor andersoni, does not elicit or inhibit humoral immune responses from immunocompetent D. andersoni or Ixodes scapularis cell lines

“…Bacterial challenge causes immunocompetent tissues to produce several soluble antimicrobial factors, including defensin and lysozyme. Defensins are small cationic antimicrobial peptides with activity against gram positive bacteria (2,3) that have been identified in several hard ticks including Dermacentor variabilis (3) and Ixodes scapularis (4,5). Lysozymes hydrolyze the 1-4 β linkage between the N-acetyl-muramic acid and N-acetyl-D-glucosamine residues that make up peptidoglycan in bacterial cell walls (6).…”