Two novel Salp15‐like immunosuppressant genes from salivary glands of Ixodes persulcatus Schulze tick

Abstract

Salp15, a 15-kDa tick salivary gland protein, is known for several suppressive activities against host immunity and critical functions for the transmission of Lyme borrelia in Ixodes scapularis and Ixodes ricinus, the major vectors found in North America and Western Europe. Salp15 inhibits the activation of cluster of differentiation (CD)4(+)T-cells through the repression of T-cell receptor (TCR)-triggered calcium fluxes and interleukin (IL)-2 production. Furthermore, Salp15 adheres to the spirochaeta and specifically interacts with its outer surface protein C. The binding of Salp15 to Borrelia burgdorferi protects it from antibody-mediated killing in vitro. The aim of this study is to identify the Salp15 genes in Ixodes persulcatus Schulze, the specific vector for human Lyme borreliosis in Japan. Two cDNA clones encoding the Salp15-like sequence were obtained from salivary glands of fed female ticks. These genes encode 135- and 132-amino acid proteins, designated Salp15 Iper-1 and Salp15 Iper-2, respectively, both having signal peptide sequences and predicted to be secretory proteins. Salp15 Iper-1 and -2 showed 51.8 and 68.2% similarity to I. scapularis Salp15, respectively. Reverse transcriptase PCR analysis showed that Salp15 Iper genes were expressed specifically in the salivary glands throughout life cycle stages of the ticks and were up-regulated by blood feeding. In the I. persulcatus-derived sequences, the C-terminal part, which is the binding domain to the CD4 molecule of T-cells in I. scapularis Salp15, was well conserved. In the future, it will be necessary to analyse immunosuppressive functions of I. persulcatus Salp15 and their interaction with Borrelia spp. in Japan.

IrSPI, a Tick Serine Protease Inhibitor Involved in Tick Feeding and Bartonella henselae Infection

“…exploits the salp15 tick protein and is able to induce its expression in order to facilitate mammalian host infection. Based on these results reported for Borrelia [48], [49], it is then possible to speculate that Bartonella sp. are also capable of increasing the production of some of the salp15 proteins to facilitate their transmission to the vertebrate host.…”

Tick salivary compounds: their role in modulation of host defences and pathogen transmission

“…Evidence was also provided that the pathogen B. burgdorferi in I. scapularis exploits Salp15 during transmission to a vertebrate host, as it specifically interacts with B. burgdorferi outer surface protein C (OspC) and the binding of Salp15 protects B. burgdorferi from antibody-mediated killing in vitro (Ramamoorthi et al, 2005). Salp 15-like sequences encoding proteins of the Salp family have also been identified in salivary glands of Ixodes pacificus, I. ricinus , and I. persulcatus , which are other major vectors of disease agents in the USA and Eurasia (Hovius et al, 2007; Hojgaard et al, 2009; Mori et al, 2010). The results suggest that the Salp15 homologues can be involved in host immunomodulation and transmission of Borrelia species in the above regions.…”

Genetic Diversity of Salp15 in the Ixodes ricinus Complex (Acari: Ixodidae)

“…The known Salp15 sequences were predicted to contain a signal peptide in their N-terminus which would be cleaved during protein expression [18], [27], [28], [36] (Fig. 1).…”

“…Because of these properties, scientists have suggested that Salp15 could be a potential target for the development of vaccines against Lyme spirochetes [24], [25], [26]. Recently, Salp15 homologues have been characterized from some species in the Ixodes ricinus complex in different parts of the world [14], [18], [27], [28]. However, no comparable information is available on Salp15 in Ixodes persulcatus and I. sinensis , two members of the Ixodes ricinus complex from China.…”