Insects injected with cholera toxin displayed normal behavior and no mortality after 24 h incubation negating pharmacological effects on hemocyte
behavior. Increasing cAMP levels with drugs decreases lepidopteran hemocyte adhesion to slides and was used to explain raising plasma hemocyte counts, implying these cells may dissociate from the internal tissues [45] and [34]. Levels of hemocytic intracellular cAMP were not discernibly altered by CTX [CTX concentrations (nM): 0: 0.093±0.017 pmol/106 cells; 1.2: 0.070±0.021 pmol/106 cells; 6: 0.091±0.016 pmol/106 cells; 120: 0.089±0.023 pmol/106 cells] or CTB [CTB concentrations (nM): 0: 0.089±0.040 pmol/106 cells; 6: 0.099±0.030 pmol/106 cells; 30: 0.073±0.031/pmol 106 cells; 600: 0.094±0.034 pmol/106 cells] suggesting CTX may trigger a cAMP-independent mechanism modulating the hemocyte nodulation response. Nonattached CTA also had no effect on intracellular cAMP levels [CTA concentrations Navitoclax in vivo (nM): 0: 0.063±0.010 pmol/106 cells; 1.2: 0.055±0.010 pmol/106 cells; 6: 0.038±0.006 pmol/106 cells; 120: 0.054±0.02 pmol/106 cells]. Only pharmacological CTX levels
(3 μM) stimulated cAMP in hemocytes (0.251±0.025 pmol/106 cells) above control levels, suggesting CTX can enter the hemocytes and elevate cAMP levels. Inexplicably, CTA at similar levels reduced intracellular cAMP below the sensitivity of the bioassay, while high levels of CTB (21μM) had no effect on levels of intracellular cAMP. cAMP affects insect Selleckchem Sirolimus immunological hemocyte activities [11], [45] and [34], including those remaining in circulation after reactions with non-self-materials [21] and [22]. Pharmacological amounts of CTX are known to affect cAMP levels in lepidopteran and orthopteran insect tissues [8], [46] and [73].
The holotoxin and its subunit CTB affect protein kinase A and C activity [18] and integrin–raft binding [50] in larval lepidopteran hemocytes. When applied herein at uniquely low levels for insects CTX affects Galleria mellonella hemocytes based on the 4��8C CTX concentration-dependent bimodal adhesion of hemocytes to glass, RGD-mediated hemocyte–hemocyte microaggregations, bimodal changes in total hemocyte counts in vivo and toxin-stimulated in vivo nodule formation correlating with toxin-induced bacterial removal from the larval hemolymph. Hemocyte responses induced by CTB mimic the effects seen with higher CTX concentrations suggesting part of the hemocytic response to CTX is caused by CTB. Domingos et al. [26] describe similar results for LPS-induced TNF-α release from macrophages but when the CTX concentration is low cytokine release is inhibited by the CTA moiety. Isolated CTA did not affect any of the present hemocyte responses or cAMP production at any level tested; however the diminished hemocytic responses at low CTX concentrations may reflect the CTA moiety bound to the holotoxin.