A secreted C-type lectin in Periplaneta americana functioning in antibacterial activity, innate immune signaling and leg regeneration

Total PaSCLec (PaSCL-Ad and PaSCL-Reg) was most highly expressed in the hemolymph and was significantly upregulated after challenge with <i>Escherichia coli</i> and Staphylococcus aureus. Both recombinant proteins bound lipopolysaccharides, peptidoglycan, mannan, and β-glucan in a dose-dependent manner, and agglutinated Gram-positive (<i>Staphylococcus aureus</i>, <i>Bacillus subtilis</i>) and Gram-negative (<i>Escherichia coli</i>, <i>Salmonella Typhimurium</i>) bacteria in a Ca²⁺-dependent manner. rPaSCL-Ad inhibited the growth of all tested bacteria and potentially compromised the membrane integrity of <i>E. coli</i> in a Ca²⁺-independent manner. Both recombinant proteins enhanced hemocyte phagocytic activity by promoting bacteria-hemocyte interactions. Knockdown of <i>PaSCLec</i> reduced the expression of multiple antimicrobial peptides and transcription factors associated with the Toll, IMD, and JAK/STAT signaling pathways; these effects were partially rescued by recombinant protein supplementation. In addition, <i>PaSCLec</i> knockdown impaired leg regeneration. qRT-PCR suggested an association between <i>PaSCLec</i> activity and JAK/STAT-related genes during regeneration. These findings demonstrate that <i>PaSCLec</i> is a multifunctional secreted lectin involved in microbial recognition, immune effector regulation, and leg regeneration in <i>P. americana</i>, although the underlying molecular mechanisms require further investigation.