Enhanced behavioral immune defenses in a C. elegans C-type lectin-like domain gene mutant.

C-type lectin-like domain (CTLD) proteins occupy crucial functions in the immune system of vertebrates, but their role in invertebrate immunity is much less understood. The nematode Caenorhabditis elegans possesses a highly diverse CTLD protein encoding (clec) gene repertoire. A role of C. elegans clec genes in pathogen defense is always assumed, yet experimental evidence for clec immune function is rare. To systematically test the potential function of clec genes in the C. elegans defense against pathogens, we screened 39 clec mutants for survival on the Gram-positive pathogen Bacillus thuringiensis (BT18247) and 37 clec mutants on the Gram-negative pathogen Pseudomonas aeruginosa (PA14). We found that clec mutants can exhibit either decreased or, unexpectedly, increased resistance to infection. Since we observed high escape behavior for some of the clec mutants on BT18247 during the initial screen, we then asked if increased pathogen avoidance behavior underlies the increased resistance of some clec mutants. We thus tested lawn leaving behavior of the resistant clec-29(ok3181), clec-34(ok2120), clec-151(ok2264), and C54G4.4(ok2110) mutant on BT18247. We found that C54G4.4(ok2110) mutant animals exhibit a particularly strong lawn leaving behavior, in addition to prolonged feeding cessation when exposed to BT18247. Together, our results indicate that clec genes mediate both resistance and susceptibility to infection. Further, behavioral analyses of the C54G4.4(ok2110) mutant implicate C54G4.4 in the regulation of pathogen avoidance behavior towards BT18247. We conclude that C. elegans clec genes may act both as positive and negative regulators of physiological as well as behavioral immune defense responses.