Physiological evidence of integrin-antibody reactive proteins influencing the innate cellular immune responses of larval Galleria mellonella hemocytes: Integrin-ARP affects larval Galleria hemocytes

Larval Galleria mellonella (L.) hemocytes form microaggregates in response to stimulation by Gram-positive bacteria. Hemocyte adhesion to foreign materials is mediated by the cAMP/ protein kinase A pathway and the beta-subunit of cholera toxin using a cAMP-independent mechanism. Cholera toxin-induced microaggregation was inhibited by the integrin inhibitory RGDS peptide, implying integrins may be part of the mechanism. Based on the types of mammalian integrin-antibody reactive proteins affecting hemocyte adhesion and bacterial-induced responses alpha5 , alphav , beta1 , and beta3 subunits occurred on both granular cell and plasmatocyte hemocyte subtypes. A fluorescent band representing the binding of rabbit alpha5 -integrin subunit antibodies occurred between adhering heterotypic hemocytes. The frequency of the bands was increased by cholera toxin. The alpha5 and beta1 rabbit integrin subunit antibodies inhibited removal of Bacillus subtilis (Cohn) from the hemolymph in vivo. A alpha5 beta1 -specific synthetic peptide blocker similarly diminished hemocyte function whereas the alphav beta3 -specific inhibitory peptide and the corresponding integrin subunit antibodies did not influence nonself hemocyte activities. Western blots revealed several proteins reacting with a given integrin-antibody subtype. Thus integrin-antibody reactive proteins (which may include integrins) with possible alpha5 and beta1 epitopes modulate immediate hemocyte function. Confocal microscopy established plasmatocyte adhesion to and rosetting over substrata followed by granular cell microaggregate adhesion to plasmatocytes during early stage nodulation.