Modes of phagocytosis of Gram-positive and Gram-negative bacteria by Spodoptera littoralis granular haemocytes

Haemocytes are the main immunocompetent cells in insect cellular immune reactions. Here, we show that in Spodoptera littoralis, granular haemocytes are the primary phagocyte haemocytes, both in vivo and in vitro. The “trigger” and “zipper” modes of engulfment known in mammal macrophages are active, in vivo, in S. littoralis granular haemocytes, together with macropinocytosis. Lipopolysaccharide as well as lipoteichoic acid inhibit the binding of both Gram-positive (Corynebacterium xerosis) and Gram-negative (Escherichia coli) bacteria on granular haemocytes. In addition, different ligands can inhibit the binding of E. coli. Most of these inhibitors are known as ligands of scavenger receptors in mammal macrophages and we hypothesise that one of the receptors present on S. littoralis granular haemocytes could be a scavenger-like receptor.