Figure 6.

Comparison of Toll pathways among mammals, Drosophila, and shrimp. In mammals, lipopolysaccharide (LPS) activates the Toll-like receptor (TLR) pathway by directly binding to the TLR4 receptor. In Drosophila, G⁺ bacteria or fungi activate the Toll pathway by functional Spätzle binding to Toll. In shrimp, G⁺ bacteria and G⁻ bacteria all can activate the Toll pathway by their pathogen-associated molecular patterns directly binding to Toll receptors. In shrimp, Toll receptors can directly bind to G⁺ and G⁻ bacteria, whether the Spätzles participated in the Toll pathway (like Drosophila) in shrimp still needs further study.