As described in Section 2.6, the cell-free hemolymph samples (1 µl, CH or IH) from naive or bacteria-injected larvae and 20 mM Tris-HCl, pH 7.5 (18 µl) were separately incubated with 1 µl of the buffer, purified SPHs (20 ng), PAP1 (20 ng), or PAP3 (20 ng) at room temperature for 15 min. In the control set, proPOs (100 ng, 1 µl) was either incubated with the buffer (19 µl) or buffer (17 µl) with purified SPHs (20 ng, 1 µl) and PAP3 (20 ng, 1 µl) on ice for 1 h. PO activities in the control and test samples were determined and plotted in the bar graph as mean ± SEM (n = 3).