Ultrastructural Comparison of Extracellular and Intracellular Encapsulation of Brugia malayi in Anopheles quadrimaculatus

Abstract

Ultrastructural aspects of extracellular humoral encapsulation of microfilariae of Brugia malayi in the hemocoel of Anopheles quadrimaculatus were compared with those of intracellular encapsulation of first-stage larvae (L1) of the same parasite species, in the thoracic muscle cells of the same species of mosquito. The results showed that extracellular humoral encapsulation of microfilarial sheaths, and sheathed and exsheathed microfilariae, in the hemocoel of mosquitoes occurs around the parasite within the first 6 hr postingestion, apparently without initial participation of hemocytes. Hemocytes and their remnants were observed near the parasite during the first 6 hr postingestion. Within the next 24 hr, hemocytes attach to the initial humoral capsule. By contrast, intracellular encapsulation of L1S is initiated by the accumulation of a dense cytoplasmic layer derived from the infected thoracic muscle cell. Melanin deposits accumulate in this layer adjacent to the parasite cuticle, again without visible participation of hemocytes.

Cellular-Mediated Reactions to Foreign Organisms Inoculated into the Hemocoel ofAnopheles albimanus(Diptera: Culicidae)

“…The presence of oenocytoids in the hemocoel was reported in An. quadrimaculatus Say after injection of microÞlariae (Chikilian et al 1994). Oenocytoids have been identiÞed embedded in abdominal fat body of Ae.…”

“…These responses include phagocytosis, nodule formation, cellular and humoral encapsulation (Chen and Laurence 1985, Gupta 1991, Chikilian et al 1994, and the production of anti-microbial peptides (Boman and Hultmark 1987, Hoffmann and Hoffmann 1990, Lowenberger et al 1996. The type of reaction and its intensity depends on the size, number and surface properties of the foreign particles (Lackie 1988, Wiesner and Gö tz 1993, Paskewitz and Riehle 1994, but the responses to different invaders vary among insects.…”

Molecular approaches to mosquito parasite interactions

“…Encapsulation against parasitoids or parasites has been studied by electron microscopy in several insects (for example, see Paskewitz et al, 1988;Chikilian et al, 1994;Russo et al, 1996). It occurs first with the formation of electron-dense materials (melanin) around the foreign objects, sometimes in association with lysis of hemocytes.…”

“…In the hemolymph, a melanin-like material is first deposited around the filarial larva, followed by the spreading of hemocytes. Intracellular encapsulation in the flight muscle cells occurs by deposition of cytoplasmic materials followed by melanin deposition, without the apparent participation of hemocytes (Chikilian et al, 1994).…”

Genetics of Mosquito Vector Competence

“…Since the days of Ross' black spores, which represent melanized ookinetes and oocysts (205), it has long been known that mosquitoes can melanize pathogens. This melanization response usually is mediated by hemocytes (34,39,74,265) and culminates with the deposition of melanotic materials around the pathogen. This response has been observed in all mosquitoes studied to date, including mosquitoes susceptible to parasite development (185).…”