The Salivary Gland Complex

Liu et al. (2019, Journal of Proteomics) identified 434 full-length protein sequences in leech SGS using LC-MS/MS proteomic analysis, a count now expanded to 440+ with 2025 discoveries including a novel cysteine-rich anticoagulant (Manuvera et al., Biomolecules), hirunipin-2 antimicrobial peptide (Advanced Science), and three novel AMPs (Serebrennikova et al., IJMS). Complementing this, Kvist et al. (2020, Scientific Reports) used combined transcriptomic and proteomic approaches to characterize the salivary secretome. Of these, 39 orthologous clusters are shared across the three primary Hirudo species (H. medicinalis, H. verbana, H. orientalis), suggesting core functional conservation despite millions of years of divergent evolution.

The study employed RNA-seq of salivary gland tissue combined with mass spectrometry (LC-MS/MS) of secreted proteins, providing both transcript-level and protein-level confirmation. This dual-evidence approach increases confidence in the identified secretome. In 2025, additional discoveries — extracellular vesicle biogenesis in leech salivary gland cells (ScienceDirect) and functional hirudin production in microalgae (bioRxiv) — opened new avenues for drug delivery and scalable recombinant production.

The three primary medicinal leech species share a conserved core secretome but also express species-specific variants. H. verbana, the most commonly used species in U.S. clinical practice, shows the highest expression levels for hirudin and destabilase. H. medicinalis produces a broader range of protease inhibitor variants. H. orientalis, used primarily in Eastern European and Asian practice, has a distinct profile of antimicrobial peptides.

These differences have practical implications: the choice of species may influence the pharmacological profile delivered during therapy, though clinical significance remains an open research question.