Previous studies showed that crude antigens from Trichinella spiralis adult worms (AW) can be recognized by mouse infection sera at 8 days post infection. The aim of this study was to identify the early diagnostic antigenic bands in soluble proteins from T. spiralis AW by Western blot using early infection sera. The affecting factors of adult recovery were firstly observed in this study, and the results showed that the maximum number of adults was collected from small intestine when the female BALB/c mice were orally infected with 4000 ML and sacrificed at 3 days post infection. The results of Western blot analysis showed that seven protein bands (31, 35.1, 39, 40.6, 41.9, 47 and 50.6 kDa) could be recognized by early infection sera as early as at 8-10 days post infection, and were strongly reacted with mouse infection sera at 11-12 days post infection. Our results suggested that the seven protein bands of T. spiralis AW soluble proteins might be the early expressed antigens during the intestinal stage of Trichinella infection and therefore have potential value for the early diagnosis of trichinellosis.

In previous studies, a Trichinella spiralis serine protease (TsSP) was identified in excretion/secretion (ES) products from intestinal infective L1 larvae (IIL1) using immunoproteomics. The complete cDNA sequence of TsSP gene was 1372 bp, which encoded 429 amino acids with 47.55 kDa. The TsSP was transcribed and expressed at all T. spiralis life cycle phases, as well as mainly located at the cuticle and stichosome of the parasitic nematode. Recombinant TsSP bind to intestinal epithelial cells (IEC) and promoted larva invasion, however, its exact function in invasion, development and reproduction are still unknown. The aim of this study was to confirm the biological function of TsSP during T. spiralis invasion and growth using RNA interference (RNAi) technology. The results showed that on 1 day after electroporation using 2.5 µM siRNA156, TsSP mRNA and protein expression of muscle larvae (ML) was suppressed by 48.35 and 59.98%, respectively. Meanwhile, silencing of TsSP gene by RNAi resulted in a 61.38% decrease of serine protease activity of ML ES proteins, and a significant reduction of the in vitro and in vivo invasive capacity of IIL1 to intrude into the IEC monolayer and intestinal mucosa. When mice were infected with siRNA 156-transfected larvae, adult worm and muscle larva burdens were decreased by 58.85 and 60.48%, respectively. Moreover, intestinal worm growth and female fecundity were evidently inhibited after TsSP gene was knockdown, it was demonstrated that intestinal adults became smaller and the in vitro newborn larval yield of females obviously declined compared with the control siRNA group. The results indicated that knockdown of TsSP gene by RNAi significantly reduced the TsSP expression and enzymatic activity, impaired larvae intrusion and growth, and lowered the female reproductive capacity, further verified that TsSP might participate in diverse processes of T. spiralis life cycle, it will be a new prospective candidate molecular target of anti-Trichinella vaccines.