Fig. 9.

An overview of the immune system in M. sexta. Pathogens and their surface molecules (in blue font) are recognized by pattern recognition receptors in the plasma or on the immune cells. A serine protease/serine protease homolog system (shown as pink pacmans) is activated by sequential proteolytic cleavage to generate active phenoloxidases and Spätzle-1. Serpins (colored triangles) modulate melanization and cytokine effects by inhibiting immune SPs. The putative intracellular pathways (Toll, Imd, MAPK-JNK-p38, JAK-STAT) are activated by cytokines (e.g., Spätzle-1) and microbial compounds (e.g., DAP-PG) through receptors, adaptors, kinases (red spheres), and transcription factors (colored ovals), which transactivate the expression of immunity-related genes (e.g., AMPs). Newly synthesized proteins either replenish the defense molecules used up in the initial reaction or serve as effectors to kill the survived pathogens. Autophagy, apoptosis, and RNA interference are involved in insect antiviral responses. The stimulatory and inhibitory steps are depicted as red arrows and blue bars, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)