The sheath of the microfilaria of Wuchereria bancrofti has albumin and immunoglobulin on its surface

Identification and location of albumin-like antigens in third-stage larva of W. bancrofti, in adult forms of Litomosoides chagasfilhoi and in the free-living nematode Caenorhabditis elegans

Antigens resembling those of host proteins have been identified on the surface of several filarial parasites, such as immunoglobulins and serum albumins. The origin of albumin-like antigens on filarial parasites remains unclear. Several authors suggested that they have been adsorbed, or that they were metabolic waste products from nutritional utilization of human albumin, or perhaps a contamination with human products. This study searched for human albumin-like antigens by Western blot and ultrastructural analyses on filarial parasites, third stage of W. bancrofti and adult females of Litomosoides chagasfilhoi, and on the free-living Caenorhabditis elegans nematode. Our results showed approximately 67kDa proteins recognized by anti-human albumin antibodies on extracts and excretory-secretory (ES) products of the third-stage W. bancrofti. Similar albumin-like proteins were also detected on the filarial parasite L. chagasfilhoi and on C. elegans extracts. The immunocytochemistry analysis showed human albumin-like antigens on similar tissues of these nematodes. These results provide evidence that these proteins have antigenic similarity and similar distribution in nematodes tissues. Our observations suggest that albumin-like antigens presented on filarial parasites are not acquired from the host, but rather are shared antigenic determinants found even in the third-stage larvae recovered from the invertebrate host.

Interaction between the blood fluke,Sanguinicola inermisand humoral components of the immune response of carp,Cyprinus carpio

The effect ofSanguinicola inermison serum antibody and complement activity inCyprinus carpiowas assessed using an ELISA and haemolytic assays. Possible immune evasion strategies were assessed using immunodetection of host proteins on the surface of the parasite. Carp acclimatized to 20 or 25 °C were infected by exposure to 500 cercariae or injected intraperitoneally with 150 cercariae, and serum monitored over a 63-day period. In cercariae-injected carp, irrespective of time and temperature, a significant increase occurred in complement activity being greatest at 25 °C. In addition, fish exposed to the cercariae ofS. inermisand maintained at 20 °C the level of complement activity was significantly higher after 5 weeks compared to controls. At 20 °C intraperitoneal injections of parasites increased serum antibody levels which peaked after 7 days. In contrast, at 25 °C, antibody levels were maintained over 63 days. Exposure of fish to infection did not appear to stimulate antibody production. Immunofluorescence studies revealed ‘host-like’ molecules on the surface of the cercarial body exposed to carp serum and adult flukes obtained directly from the fish or cultured for 24 h in L15 medium. The possible role of ‘host-like’ molecules in immune evasion is discussed and the response at different temperatures is related to infection dynamics.

Identification of a stress-responsive Onchocerca volvulus glutathione S-transferase (Ov-GST-3) by RT-PCR differential display

The effects of oxidative insult on gene transcript levels in the filarial nematode Onchocerca volvulus were investigated using differential display RT-PCR. Oxidative stress was applied with the reagents paraquat, plumbagin and xanthine-xanthine oxidase. In all three cases, a cDNA fragment encoding a novel glutathione S-transferase (GST) resembling members of the theta-class was identified as upregulated (PQ29, PG112, XOD26). The subsequently isolated full-length cDNA harbors a 753-bp open reading frame encoding a GST with 268 amino acid residues and a predicted molecular mass of 31 kDa. This stress-responsive GST (Ov-GST-3) possesses only 14 and 21% sequence identity with the other O. volvulus GSTs (Ov-GST-1 and Ov-GST-2, respectively). Interestingly, Ov-GST-3 shares higher sequence identity with GSTs that are upregulated due to environmental stress. In order to confirm the specific upregulation of the Ov-GST-3 transcripts identified by differential display and to analyze the mRNA levels of the other Ov-GSTs (Ov-GST-1 and Ov-GST-2) under elevated stress conditions, a semi-quantitative polymerase chain reaction-enzyme-linked immunosorbent assay was performed. The Ov-GST-3 gene transcript level increased dramatically in response to xanthine-xanthine oxidase and to a lesser extent with paraquat and plumbagin. In contrast, Ov-GST-1 and Ov-GST-2 did not show any significant alterations in their steady-state mRNA levels in response to oxidative stress when examining the same mRNA samples. The present study clearly demonstrates that Ov-GST-3 is a critical enzyme in the defense against oxidative stress.

Human serum albumin and immunoglobulin on Dracunculus medinensis

Dracunculus medinensis recovered from infected humans were examined for the occurrence and localization of human serum albumin and immunoglobulins. Immunoelectrophoretic examination of homogenates prepared from adult female worms (ADGW) and first stage larvae (LVGW) showed that anti-human albumin antibodies reacted to both stages of the parasite. By direct fluorescence antibody technique, antigens resembling human albumin and human immunoglobulins (isotype IgG) were identified on the surface of adult female worms. The occurrence of host-like compounds on the parasites may be an adaptation for survival of the parasites. A possible interference of these compounds should be considered in attempts to develop methods for immunological diagnosis of D. medinensis infections.

Immunocytochemical localization and distribution of human albumin in Wuchereria bancrofti adult worms

To determine whether albumin is present on adult worms of Wuchereria bancrofti, thin sections of resin-embedded parasites were incubated with a specific antiserum to human albumin. With the exception of the epicuticle, all layers of the cuticle and the hypodermis were intensely labeled. Concentration of gold particles was observed within infoldings of the hypodermal membrane. Moderate labeling of the thin basement membrane that lines the pseudocelomic cavity and the gonoduct was also observed. Within the uterus, ovular membranes labeled intensely; groups of organized particles were seen below ovular membranes and also within invaginations of microfilarial embryos. In contrast, few gold particles were seen on the surface of mature intrauterine microfilariae. No labeling was observed in control sections incubated with antiserum preadsorbed with purified human albumin. The findings suggest that human albumin may be essential for the nutrition and development of W bancrofti microfilariae.

Transglutaminase-catalyzed incorporation of host proteins in Brugia malayi microfilariae

Recently, we have characterized and purified a novel transglutaminase (pTGase) from adults of the filarial worms Brugia malayi. pTGase-catalyzed reactions seem to play an essential role during in utero growth and development of microfilariae. The results presented here demonstrate that exudates from the peritoneal cavity of jirds, the site where adult worms of B. malayi reside and produce microfilariae, contain several host proteins that can serve as substrates in pTGase-catalyzed reactions. The peritoneal exudate proteins are avidly taken up by adult female worms in vitro and incorporated into the developing microfilariae. Among the several host proteins that were crosslinked, a 68-kDa molecular weight protein (p68) was found to be the major protein taken up by the parasites. Following uptake by the parasites, the peritoneal exudate proteins are crosslinked to form high molecular weight aggregates, that are subsequently incorporated into in utero developing embryos and microfilariae. The cross-linking of host proteins was, however, inhibited by monodansylcadaverine (MDC), a competitive inhibitor of pTGase. Antibodies raised against the jird peritoneal exudate proteins strongly immunoreacted with a 68-kDa protein in adult worms and microfilariae extracts but not with infective-stage larvae (L3) of B. malayi. These results suggest that pTGase is involved in covalent incorporation of host proteins (such as p68) into developing embryos and microfilariae of B. malayi.