Specific histamine binding activity of a new lipocalin from Hyalomma asiaticum (Ixodidae) and therapeutic effects on allergic asthma in mice

BACKGROUND: Lipocalin proteins are secreted by tick salivary glands as an important strategy to interfere with the immune response of hosts. A large number of lipocalins are secreted, but the functions of most of these proteins are unclear. Here, we report a new lipocalin protein with particular histamine binding capacity, which was isolated from the salivary glands of the tick Hyalomma asiaticum. METHODS: The full length cDNA of the Ha24 gene was obtained by RACE, and Ha24 gene was expressed in E. coli; after protein purification and mice immunizations, specific Polyclonal antibodies (PcAb) were created in response to the recombinant protein. Reverse transcription PCR (RT-PCR), Quantitative PCR (Q-PCR), indirect immunofluorescence antibody (IFA) assay and western blot were used to detect the existence of native Ha24 in ticks. To confirm the histamine-binding capacity of rHa24, a histamine-binding assay was completed in vitro (ELISA) and in vivo by inhibition of allergic asthma in mice. RESULTS: Ha24 is coded by 681 bases, contains 227 amino acids, and has a molecular weight of 23.3 kDa. Abundant expression in the salivary glands of feeding ticks was confirmed by the identification of native Ha24 in ticks. The results of a histamine binding assay both in vitro and in vivo demonstrated that rHa24 binds specifically with histamine in a dose-dependent manner, and can provide relief from allergic asthma in mice. CONCLUSIONS: Ha24 is a new tick lipocalin with specific histamine binding activity that can provide relief from host inflammation response.