Haemaphysalis longicornis HSP20 inhibits Rickettsia heilongjiangensis replication by targeting the pathogen 50S ribosomal protein

Abstract Background The tick Haemaphysalis longicornis is a major vector for several zoonotic pathogens, including Rickettsia heilongjiangensis . Small heat-shock proteins (sHSPs) are critical for stress responses and host–pathogen interactions. Among them, the HSP20 gene was found upregulated during rickettsial infection, whereas its specific function at the host–pathogen interface remains undefined. Methods The full length of the HSP20 gene ( HlHSP20 ) and its expression profile was characterized in H. longicornis , and RNA interference (RNAi) was used to knockdown HlHSP20 , followed by the quantification of R. heilongjiangensis proliferation. Proteins from R. heilongjiangensis interacting with HlHSP20 were identified using GST pulldown coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS) and validated by yeast two-hybrid (Y2H) assays. Results HlHSP20 is a conserved, non-transmembrane intracellular sHSP with a αB-crystallin domain, showing the highest expression in egg and larval stages. The knockdown of HlHSP20 significantly promoted the proliferation of R. heilongjiangensis , and interaction screening revealed that HlHSP20 specifically binds to the 50S ribosomal protein L14 (RhRPL14) of R. heilongjiangensis . Conclusions The present study demonstrates that HlHSP20 acts as a host restriction factor against R. heilongjiangensis in H. longicornis , likely through a direct interaction with the pathogen ribosome protein. This work unveils a novel component of the antimicrobial defense of ticks and identifies HlHSP20 as a potential target for disrupting rickettsial transmission. Graphical Abstract