Ll. Pech et Mr. Strand, GRANULAR CELLS ARE REQUIRED FOR ENCAPSULATION OF FOREIGN TARGETS BY INSECT HEMOCYTES, Journal of Cell Science, 109, 1996, pp. 2053-2060
Haemocytes play an essential role in defending invertebrates against p
athogens and parasites that enter their haemocoel, A primary defense r
esponse is encapsulation; a process in which haemocytes attach to the
foreign organism and kill it. Whether encapsulation requires cooperati
on between specific subpopulations of haemocytes is unknown, Using pur
ified subpopulations of haemocytes and an in vitro encapsulation assay
, we investigated the process of capsule formation in the insect Pseud
oplusia includens. Immunocytochemical staining revealed that capsule f
ormation involves a three step process, Encapsulation began when granu
lar cells attached to the foreign target, This was followed by attachm
ent of multiple layers of plasmatocytes. Termination of capsule format
ion occurred when a subpopulation of granular cells formed a monolayer
around the periphery of the capsule, Neither granular cells nor plasm
atocytes were capable of forming a capsule independently, However, pla
smatocytes encapsulated targets if granular cells were present or if t
argets were preincubated in medium conditioned by granular cells, The
effect of granular cell-conditioned medium could be blocked by the add
ition of the cell adhesion recognition sequence, RGDS, but not by RGES
, These results demonstrate experimentally that granular cells are req
uired for encapsulation of foreign targets by plasmatocytes in vitro,
and that the role of granular cells in this process involves an RGD-de
pendent cell adhesion mechanism.