Fig. 1

Toll pathway, Imd pathway, and complement system in metazoans. A Toll pathway, B Imd pathway, and C. complement system in Drosophila and vertebrates. Dashed arrows indicate indirect processes. D Presence and absence of proteins belonging to the Toll and the Imd pathways and to the complement system across metazoans. Orthologs of components of the Imd pathway have been found in vertebrates; however, these components belong to the vertebrate TNFα pathway, which is analogous to the arthropod Imd pathway. Grayish compartments within each pathway compartment indicate proteins that are uncertain to be involved in the pathway. Black circles indicate that the protein is present for that taxon, while white circles indicate its absence. For C1q, FreD-C, and C-lectin proteins, black circles with an asterisk (*) indicate the presence of proteins with collagen domains (C1qL, ficolin, and MBL/GBL, respectively), while only black circles indicate the presence of C1q, FreD-C, and C-lectin proteins containing coiled-coil regions instead of collagen domains (FreDC2 and CTLDC2). Nemertean phylogenetic position is highlighted in bold. AP, alternative pathway; B, Bilateria; CP, classical pathway; Cyt, cytoplasm; D, Deuterostomia; E, Ecdysozoa; EC, extracellular space; Fb, factor B; LP, lectin pathway; N, nucleus; P, Protostomia; S, Spiralia; tPGRPs: long transmembrane PGRPs. For references for D, view Additional file 1: Table S1. Phylogeny according to [6]