FOLLOW-UP OF PROTEIN RELEASE FROM PSEUDOPLUSIA-INCLUDENS HEMOCYTES - A FIRST STEP TOWARD IDENTIFICATION OF FACTORS MEDIATING ENCAPSULATION IN INSECTS

Hemocyte types involved in encapsulation were characterized using mono clonal antibodies (mAbs). This approach revealed that four hemocyte ty pes in Pseudoplusia includens could be classified into two antigenical ly distinct cell lines. The first line comprised granulocytes (GR) and spherulocytes (SP) and the second line comprised plasmatocytes (PL) a nd oenocytoids (OE). One of the mAbs labeled a subpopulation of plasma tocytes that spread on culture plate surfaces. This subclass represent ed approximately 70 % of all plasmatocytes. The cytoplasmic punctate s taining of granulocytes clearly decreased upon short term culture, sug gesting the associated antigens were released into the culture medium during cell spreading. A follow-up of protein secretion into culture m edium by Western blotting confirmed this hypothesis for both granulocy tes and plasmatocytes. In a few cases, discharged proteins exhibited a short half-life suggesting they may behave as regulatory molecules. A mong them, plasmatocyte proteins of +/- 25 kDa might be mobilized at a n early stage of encapsulation. The same proteins appeared to accumula te at the periphery of the median plasmatocyte multilayer in late caps ules. This location coincides with where an outer monolayer of granulo cytes attaches and causes termination of capsule growth. These prelimi nary results raise the possibility that released proteins regulate hem ocyte recruitment during encapsulation.