Surface characterization of the cuticle of dirofilaria immitis

Abstract

The surface reactivity of the dog heartworm (D. immitis) was evaluated by comprehensive contact angle measurements and a platelet retention test. Contact angle data yielded calculated surface energy terms very similar to those previously reported for intact vascular endothelium. The platelet test revealed the native worm surface to be nonreactive, retaining fewer platelets than glass or worms whose surfaces had been modified by extraction with acid and high salt solutions. The cuticular morphology of the heartworm was studied with both light and electron microscopy, the latter coupled with ferritin-conjugated double-layer immunolabeling to reveal adsorbed host protein on the cuticle surfaces. Multiple attenuated internal reflection (MAIR) IR spectroscopy confirmed the general composition of this surface layer to be glycoproteinaceous. Morphological and histochemical studies confirmed and extended previous descriptions of nematode cuticle, adding ultrastructural detail on cortical, medial, and basal layers. A trilaminar membrane, apparently corresponding to a mammalian cell membrane (plasmalemma), constituted the external cortical layer as observed in high magnifications. The existence of a glycocalyx of varying thickness was demonstrated in ruthenium red-stained sections. MAIR IR spectra showed this glycoproteinaceous film to appear, in fully hydrated samples, as a loose biological gel. Ferritin-antibody conjugate labeling confirmed the presence of adsorbed dog albumin, dog immunoglobulin class G (IgG) and dog complement fraction 3 (C3) in the cuticular surface layer. It is likely, therefore, that D. immitis heartworms demonstrate long-term thromboresistance at least in part due to their passive low-surface-energy overcoating with host proteins.

Human and Animal Dirofilariasis: the Emergence of a Zoonotic Mosaic

“…In the space between the layers, fibers reminiscent of collagen surround keratin-like material, the arrangement of which confers flexibility to the worms, which is required for their survival. The epicuticle is lined with a thin glycocalyx (1,48,233,234,265). Nematode molting is regulated by ecdysteroid hormones, which play a similar role in insects (31 20-hydroxyecdisone (DiEcR) that shares multiple biochemical features with a similar receptor in insects has been identified in D. immitis and characterized.…”

“…Adult worms have developed additional long-term immune evasion mechanisms. The external surface of D. immitis adults can capture platelets and adsorb albumin, IgG, and complement fraction 3 (C3) in dogs (48,190), thereby masking the worms and preventing the recognition of cuticular antigens. A nonimmunogenic 6-to 10-kDa glycolipid associated with the surface of adult worms may constitute a barrier against protease activity at the epicuticle-host interface, also contributing to the evasion mechanisms (381).…”

Intraocular localization ofOnchocerca lupiadult worm in a dog with anterior uveitis: A case report

“…from Dirofilaria spp. 26,39 In the present case, ophthalmic examination and direct visualization of the parasite within the anterior chamber enabled easy diagnosis in this dog and helped explain the conjunctival and uveal signs. Diagnosis was also supported by the negative test for Dirofilaria immitis (Snap â Canine Heartworm PF; IDEXX) and the peripheral eosinophilia.…”

“…The above morphological characteristics help significantly to differentiate Onchocerca spp. from Dirofilaria spp …”

Molecular Characterization of a Dirofilaria immitis Cysteine Protease Inhibitor (Cystatin) and Its Possible Role in Filarial Immune Evasion

“…Given that D. immitis worms are continuously exposed to the host immune system, and yet can achieve a lifespan of years, they must engage in various immune evasion strategies [8]. During short-term immune evasion, infective larvae avoid host immune responses by releasing surface antigens, whereas in long-term immune evasion, pre-adult and adult worms mask their surface by adsorbing different host molecules and cells [9,10].…”