Regulation of melanization by glutathione in the moth Pseudoplusia includens

Hemolymph Melanization in the Silkmoth Bombyx mori Involves Formation of a High Molecular Mass Complex That Metabolizes Tyrosine

“…In M. sexta, free Tyr levels near 1 mM were reported, whereas DOPA and other catecholamines were found to not exceed 50 M (20, 21). In P. includens and A. aegypti, free Tyr was ϳ100 M, whereas DOPA levels were ϳ1 M (A. aegypti) (19) or undetectable (P. includens) (7).…”

“…Dopaquinone and dopamine-quinone thereafter proceed through a series of unstable intermediates, such as dopachrome and dopaminechrome, that result in formation of melanin (2). The standard method for monitoring these events in the PO cascade literature is by measuring absorbance in a sample at or near 470 nm, which predominantly detects dopachrome and/or dopaminechrome rather than melanin itself (2,7). Here, we monitored melanization of plasma by measuring absorbance at 470 nm at 3-min intervals using a BioTek Synergy 4 plate reader.…”

“…Preparation of Substrate-free Plasma (SFP)-B. mori plasma was prepared as described above except that larvae were bled directly into PBS containing GSH (1 mM final concentration) to inhibit melanization (7). Other samples were bled into PTU (1 mM) or 3-iodotyrosine (1 mM).…”

“…Once present, PO activity usually localizes to the surface of foreign targets or wound sites, which limits global melanization of hemolymph. Endogenous protease inhibitors like serpins act as negative regulators of serine proteases in the PO cascade (6), whereas reducing agents like glutathione (GSH) prevent the formation of melanin (7). Several pathogens of insects, including polydnaviruses, also produce molecules that suppress the melanization response of hosts (1,8).…”

Predator stress-induced immunosuppression: trade-off, immune redistribution or immune reconfiguration?

“…Finally, we measured glutathione (GSH) levels in the haemolymph because predator exposure induces oxidative stress damage in insects (Janssens and Stoks, 2014). GSH is a major antioxidant in insects and plays a role in immune function (Clark et al, 2010). Moreover, ants exposed to chronic social stress show a reduction in GSH (Schneider et al, 2016).…”