Studies have shown that the humoral defense mechanism of silkworms against bacterial infection includes the enhanced expression of several pattern recognition receptors (PRRs), PGRP-S1-S3, PGRP-L1-L3, βGRP3 and 4, which respond to both Gram-positive and Gram-negative bacteria [18,32,57]. The gene discussed is PGLYRP1; the disease is bacterial infectious disease.