Cell-mediated immunity in insects includes phagocytosis, nodulation, encapsulation, and melanization, and is primarily mediated by the hemocytes or blood cells. The majority of blood cells constitute the macrophage-like plasmatocytes (90-95% of hemocytes in Drosophila that are specialized in the engulfment and degradation of cellular debris, debris and invading pathogens. (Swevers et al. 2018 and references therein, FBrf0238851.)

In Drosophila, the major RNAi pathway involved in antiviral immunity is initiated by the processing of virus-derived dsRNA molecules to viral small interfering RNAs (viral siRNAs or vsiRNAs) by Dicer-2 (Dcr-2) enzyme. Viral siRNAs are subsequently loaded in an effector complex named RISC (RNAi-induced silencing complex) with Argonaute 2 (AGO2) as central molecule. SiRNA-programmed RISC complexes subsequently scan cellular RNA populations for complementary sequences and cause specific RNA degradation after specific siRNA-mRNA hybridization. The central factors of the siRNA pathway, Dcr-2 and AGO2, were demonstrated to have undergone accelerated evolution as a consequence of adaptive virus-host arms races. (Swevers et al. 2018 and references therein, FBrf0238851.)