Figure 5.

Model of hemocyte lineages during development. The two functional classes of embryonic hemocytes are the embryonic macrophage and crystal cells. Lymph gland hemocyte precursors, although present are not active until later in development. Hemocytes are able to differentiate and alter cell identity through known (solid line) and less-well characterized (dashed line) pathways. The late stage larva has three hemocyte types; plasmatocytes, crystal cells, and lamellocytes. Plasmatocytes originate from either the embryonic macrophage, or upon immune induction, from the lymph gland. Either source of plasmatocyte/prohemocyte can give rise to lamellocytes. All three cell types participate in wasp egg encapsulation. Exposure to wasps alters the dynamics of this process. We suggest that the maternal depression of PGRP-LB in the late stage oocyte impacts one or both of the embryonic tissues through an unknown mechanism (red question marks). This maternal signal alters the tissue(s) in a way that will enhance the differentiation of lamellocytes later in development (red asterisk).