Partial characterization of the adsorbed protein layer on Dirofilaria immitis (Nematoda) cuticle

Electron microscopy coupled with ferritin-conjugated indirect immunolabeling was used to locate sites of adsorbed host protein on cuticular surfaces of the adult canine heartworm, Dirofilaria immitis. The epicuticle appeared as a trilaminated structure. At high magnifications, the outermost layer of this structure was resolved into a trilaminar layer, which might correspond to the plasma membrane of animal cells. A ruthenium red-positive layer was external to the epicuticle. Ferritin-antibody conjugates showed evidence of adsorbed dog albumin, dog immunoglobulin class G (IgG), and dog complement fraction 3 (C3) on the surface. Ferritin adsorption to control surfaces was minimal. Possible causes and effects of interfacial host-protein adsorption are discussed in an attempt to bring insight to the hemocompatible nature of the parasitic cuticle.