PT  - JOURNAL ARTICLE
AU  - Andrea Orús-Alcalde
AU  - Aina Børve
AU  - Andreas Hejnol
TI  - The Toll and Imd pathway, the complement system and lectins during immune response of the nemertean <em>Lineus ruber</em>
AID  - 10.1101/2022.04.26.489627
DP  - 2022 Jan 01
TA  - bioRxiv
PG  - 2022.04.26.489627
4099  - http://biorxiv.org/content/early/2022/04/28/2022.04.26.489627.short
4100  - http://biorxiv.org/content/early/2022/04/28/2022.04.26.489627.full
AB  - Innate immunity is the first line of defense against pathogens. In animals, the Toll pathway, the Imd pathway, the complement system, and lectins are well-known mechanisms involved in innate immunity. Although these pathways and systems are well understood in vertebrates and arthropods, they are understudied in other invertebrates. In order to shed light on immunity in the nemertean Lineus ruber, we performed a transcriptomic survey and identified the main components of the Toll pathway (e.g. myD88, dorsal/dif/NFκB-p65), the Imd pathway (e.g. imd, relish/NFκB-p105/100), the complement system (e.g. C3, cfb) and some lectins (FreD-Cs and C-lectins). In situ hybridization showed that TLRβ1, TLRβ2 and imd and are expressed in the nervous system, the complement gene C3-1 is expressed in the gut and the lectins in the nervous system, the blood, and the gut. To reveal their potential role in defense mechanisms, we performed immune challenge experiments, in which Lineus ruber specimens were exposed to the gram-negative bacteria Vibrio diazotrophicus. Our results show the upregulation of specific components of the Toll pathway (TLRα3, TLRβ1, and TLRβ2), the complement system (C3-1), and lectins (c-lectin2 and fred-c5). Therefore, similarly to what occurs in other invertebrates, our study shows that components of the Toll pathway, the complement system and lectins are involved in the immune response in the nemertean Lineus ruber. The presence of these pathways and systems in Lineus ruber, but also in other spiralians, in protostomes and in deuterostomes suggest that these pathways and systems were involved in the immune response in the stem species of Bilateria.Competing Interest StatementThe authors have declared no competing interest.CCPComplement Control Protein domainsCfbComplement factor BCfcComplement factor CCRComplement ReceptorFBGFibrinogen domainFreD-CFibrinogen-related domaincontaining proteinsMBLMannose-Binding LectinsMreMMASP-related MoleculesPAMPPathogen Associated Molecular PatternsPGRPPeptidoglycan Recognition Protein ReceptorPGRP-LLong Peptidoglycan Recognition Protein ReceptorPRRPathogen Recognition ReceptorsqPCRquantitative real-time PCRTLRToll receptorTrypSPTrypsin-like serine protease domainvWFvon Willebrand factorWMISHwhole mount in situ hybridization