[REGULATION OF ANTIMICROBIAL PEPTIDE SYNTHESIS IN THE LARVAE OF CALLIPHORA VICINA (DIPTERA, CALLIPHORIDAE): DOSE-DEPENDENT EFFECT OF ECDYSTEROIDS].

Ecdysteroids are multifunctional hormones regulating virtually all morphogenetic processes in insects. Their role in stress and immune response regulation is less known. Here we studied 20-hydroxyecdysone effect on synthesis of the antimicrobial peptides in larvae of Calliphora vicina. An inverse correlation was found between 20-hydroxyecdysone titer and the concentration of antimicrobial peptides in the hemolymph of unaffected and bacteria-immunized insects. High and low doses of 20-hydroxyecdysone, injected simultaneously with bacterial cells, had an opposite effect on antimicrobial peptide synthesis in the diapausing larvae. Morphogenetically effective doses of 20-hydroxyecdysone demonstrated immuno-suppressive activity. Low doses of 20-hydroxyecdysone, on the contrary, moderately stimulated synthesis of the antimicrobial peptides. These data suggest that ecdysteroids are directly involved in regulation of the immune system activity and the final effect is dose-dependent.

[Neurogenic and septic inductions of synthesis of peptide antibiotics in larvae of Calliphora vicina R.-D. (Diptera: Calliphoridae)].

Synthesis of antimicrobial peptides in diapausing larvae Calliphora vicina can be induced by two different pathways. One pathway is well known in insects and includes recognition of microbial particles by the pattern-recognizing receptors. The other pathway includes perception and transduction of stress signal to immunocompetent cells by neuroendocrine system. This phenomenon consists in stimulation of synthesis of defensins, cecropins, and diptericins under effect of chromic stimulation of mechanoreceptors with ligature applied on the larva head end. Formation of immune response in brain is established to need less than 30 s, after which isolation of the neuroendocrine complex does not eliminate activation of immune response As judging from rate of the neurogenic induction, transduction of the stimulating signal from brain to the immune system cells can be connected with release into hemolymph of biogenic amines or other neurohormones stored preliminarily in the neurohemal organ. The nature of this inductor at present remains unknown, as analysis of role of octopamine, dopamine, and adipokynetic hormone did not reveal stimulating effect on synthesis of bactericidal peptides. Physiological mechanism of this phenomenon is not finally understood, its key links seem to be CNS, hormonal factor of cardial bodies, and system of antimicrobial peptides. Synthesis of antimicrobial peptides is directly regulated by the neuroendocrine system that can produce both stimulating and stress action by reminding in this aspect the known immunoneuroendocrine interrelations in vertebrates. The existence of similar integrating mechanisms in such polar animal kingdom groups which are insects and vertebrates indicate that they are more ancient than this was considered earlier.