Identification and comparative analysis of three novel C-type lectins from the silkworm with functional implications in pathogen recognition

C-type lectins can act as pattern recognition receptors (PRRs) in innate immunity. Previously, we identified two C-type lectins from silkworm (Bombyx mori), BmLBP and BmMBP, as PRRs. In the present study, we identified three homologs of these lectins by searching the silkworm genome database. These novel B. mori low-expression lectins were designated BmLEL-1, BmLEL-2, and BmLEL-3. Although Western-blot analysis failed to detect BmLEL-1, -2, or -3 in plasma, affinity precipitation of larval plasma with various microorganisms revealed that BmLEL-1 and -2 bind to rough and smooth strains of Gram-negative bacteria, respectively. BmLEL-1, -2, and -3 were found to be expressed in testis and ovary, where BmLEL-2 expression was up-regulated after bacteria infection. These results indicate that the novel C-type lectins might play a role in the innate immunity in these tissues as PRRs. Here, we discuss the roles and members of the C-type lectins as primary PRRs in B. mori cellular immunity.