With mammalian immunocytes CTA alone does not affect the release of TNF-α from macrophages [26] and will penetrate human T cells only when conjugated to CTB or other proteins such as dimers of Staphylococcus aureus protein A [29]. Decreased hemocyte adhesion to glass caused by elevated cAMP increases the number of circulating

hemocytes in the hemocoel of G. mellonella [45] and [34], However, increases in circulating hemocytes induced by CTX and CTB at levels that do not elevate cAMP were unrelated to loss of adhesion. The increase in circulating hemocytes without loss of adhesion suggests CTX and CTB induce an elevation of adhesive hemocyte number in the hemolymph even as RGD-sensitive hemocyte aggregations occurs leading to nodulation. Hemocyte elevation, a reaction occurring in response to trauma, Dorsomorphin purchase such as infection, results in an increase in hemolymph hemocytes coinciding with the initiation of nodulation [32] and [59]. The source of these hemocytes is not known. Insect hemocytes exist in three compartments: floating in the hemolymph, in stem cell clusters

(giving rise to different types of hemocytes [42]), attached as individual differentiated cell types to various organs (including hematopoietic organs) and tissues, and in and beneath the epidermis [77], [38], [40] and [43]. Release of hemocytes from stem cell aggregates and hematopoietic organs would require time consuming differentiation and multiplication which would not be rapid enough for the present results. Hemocytes may be rapidly released into the blood from surrounding tissues by being actively mobilized or being passively mobilized LY294002 by tissue modification PLX3397 mw leading to the release of adhering hemocytes into the plasma. Hemocyte types associated with the organs and tissues seem to vary between species with plasmatocytes and/or granular cell predominating [1], [40] and [49]. In larval G. mellonella the granular cells increase in number more than plasmatocytes suggesting

that the former cell type may dominate in the various stores. In larval S. exigua, the hemocyte type most predominantly mobilized after E. coli injection is the immunosurveillant, nodulation-initiating granular cell [38], an event similar to post-CTX-injection in G. mellonella where the increase in granular cell attachment, more than the plasmatocytes, could signify the initiation of microaggregation. The discrepancy between hemocyte adhesion in vitro and in vivo at higher concentrations of CTX likely reflects the absence of hemocyte stores in vitro. Control and CTX-induced in vitro microaggregates on glass display plasmatocyte rosetting around their edges. Similar cellular composition and activity occurs for stimulated larval hemocytes in vivo and in vitro of at least three other lepidopteran species spanning different families [23] in which plasmatocyte directional movement indicated by the spread of the lobopodia is from areas of high hemocyte density to areas of low hemocyte density.