Chandrashekar R et al. (1991) J Parasitol "Effect of CGP 20376 on Brugia malayi and parasite antigenemia in jirds."

Subrahmanyam D, Chandrashekar R, Weil GJ

[J Parasitol, 1991]

This study was designed to investigate the activity of CGP 20376, a benzothiazole derivative, against Brugia malayi in jirds and to illustrate the utility of parasite antigen detection as a means of monitoring drug efficacy in filariasis. Drug treatment was 100% effective in jirds treated 3 or 24 days after infection. Microfilaria and adult worm counts were reduced (relative to counts in sham-treated control animals) by 96% and 95%, respectively, in animals treated 153 days after infection. Four of 6 animals in this treatment group cleared their microfilaremias and were free of adult worms 5 mo after treatment. Thus, CGP 20376 was effective against all life cycle stages of B. malayi in jirds. Parasite antigen levels in jird sera were consistent with parasitological results in all treatment groups, but antigen clearance was incomplete in some cases after apparently successful treatment of mature and immature infections.

Chandrashekar R et al. (2002) Parasitol Res "Dirofilaria immitis: further characterization of the transglutaminase enzyme and its role in larval molting."

Devarajan E, Mehta K, Chandrashekar R

[Parasitol Res, 2002]

We recently reported the cDNA cloning and functional characterization of a novel transglutaminase (TGase) from the dog filarial parasite Dirofilaria immitis. D. immitis TGase (DiTG) has no sequence similarity with any other known TGase, but has significant similarity to protein disulfide isomerase (PDI)-related endoplasmic reticulum protein ERp60. In the present study. we further characterized the recombinant DiTG (rDiTG) and studied its role in the molting process of third-stage larvae. The enzymatic activity of rDiTG requires Ca2+, and the maximum activity was observed at a calcium concentration of 4 mM. Interestingly, the rDiTG was highly thermostable, with optimal activity observed at 55 degrees C, similar to that seen with the native enzyme. Dithiothreitol (DTT) was not essential for enzyme activity. In fact, rDiTG was more active in the absence of DTT. The known inhibitors of TGase, such as monodansylcadaverine (MDC), cystamine and iodoacetamide, inhibited the TGase activity, but not the PDI activity, of rDiTG, demonstrating the dual activity of rDiTG. The TGase-specific pseudosubstrate, MDC, completely inhibited the molting of D. immitis L3 to L4 if present during the first 24-48 h of the molting process. Electron microscopic studies revealed that MDC-treated infective larvae failed to show separation between the L3 and L4 cuticles. The L4 cuticle and accompanying hypodermis were much thinner in MDC-treated worms than in controls. Using anti-rDiTG antiserum, the native DiTG antigen was localized in the hypodermis, afibrillar muscle cells and gut epithelium in adult male and female worms as well as developing embryos in the females.

Chandrashekar R et al. (1986) Exp Parasitol "Brugia malayi: rat cell interactions with infective larvae mediated by complement."

Rao UR, Subrahmanyam D, Parab PB, Chandrashekar R

[Exp Parasitol, 1986]

Albino rat macrophages and neutrophils, in the presence of fresh normal rat serum as a source of complement, adhered to and promoted killing of Brugia malayi infective larvae in vitro. Eosinophils, by themselves, were marginally cytotoxic at a high cell-target ratio but promoted cytotoxicity when mixed with macrophages. Eosinophil culture supernatants enhanced the macrophage mediated killing of infective larvae. The complement of fresh normal rat serum was found to act by the alternate pathway. Fresh normal rat serum depleted of alternate pathway complement activity by treatment with zymosan A, or of Factor B by heating at 50 C for 20 min, or of Factor D by passing through Sephadex G75 column, failed to promote cell adherence to the parasite. C3 molecules were detected on the surface of infective larvae by immunofluorescence. There was a significant consumption of complement when Brugia malayi infective larvae were incubated in fresh normal rat serum. Albino rat cells were more potent in inducing cytotoxicity to infective larvae in vitro than those from jird or Mastomys natalensis, which may reflect the greater resistance offered by the rat to B. malayi infection. There was much less cellular infiltration on introduction of Brugia malayi infective larvae into the peritoneal cavity of jirds compared to rats and Mastomys natalensis indicating the greater susceptibility of jirds to intraperitoneally induced infections.

Chandrashekar R et al. (1994) Mol Biochem Parasitol "Molecular cloning of Brugia malayi antigens for diagnosis of lymphatic filariasis."

Curtis KC, Chandrashekar R, Weil GJ, Ramzy RM, Li BW, Liftis F

[Mol Biochem Parasitol, 1994]

Immunological crossreactivity among nematodes has hampered development of specific serodiagnostic assays for lymphatic filariasis. In the present study, we report the molecular cloning and characterization of two filaria-specific recombinant clones (BmM5 and BmM14) with immunodiagnostic potential. BmM5 is a 505-bp cDNA which codes for a protein of 130 residues that ends with an endoplasmic reticulum targeting sequence. BmM14 is closely related to a recently reported clone (SXP-1), and it has 62% homology (deduced amino acid sequence) with a previously described Onchocerca volvulus clone, lambda RAL-2. Glutathione S-transferase fusion proteins of BmM5 and BmM14 were tested in various ELISA formats. The best results were obtained by measuring IgG4 antibodies to the fusion proteins. ELISA studies showed that approximately 90% of 111 sera from Indian and Egyptian patients with brugian and bancroftian filariasis were reactive with both antigens. Nonendemic sera as well as sera from patients with schistosomiasis or intestinal helminths were uniformly nonreactive. Assays based on BmM5 and BmM14 may be useful for large scale screening as an alternative to microfilaria or filarial antigen detection as a means of obtaining a rough index of filariasis endemicity in previously unstudied areas.

Chandrashekar R et al. (1995) J Infect Dis "Molecular characterization of a parasite antigen in sera from onchocerciasis patients that is immunologically cross-reactive with human keratin."

Weil GJ, Curtis KC, Chandrashekar R

[J Infect Dis, 1995]

Onchocerca volvulus is a nematode that causes severe dermatitis and blindness in humans. Prior studies have shown that immune complexes in sera from onchocerciasis patients contain parasite antigens with M(r) of 23,000 and 65,000-70,000. Monoclonal antibody OV-1 binds to these antigens and to corresponding antigens in adult worm extracts and in vitro culture supernatants. OV-1 was used to immunoscreen an O. volvulus adult worm cDNA library. Clone OV1CF contains a 1632-bp open-reading frame that codes for a protein with a predicted M(r) of 63,000. The deduced protein sequence of OV1CF has 78% identity with Ascaris lumbricoides intermediate filament A and 40%-50% identity with several mammalian intermediate filaments. Antibodies raised to OV1CF bind to human keratin, and some sera from onchocerciasis patients contain antibodies to OV1CF and to keratin. Thus, immune complexes from onchocerciasis patients contain a parasite antigen that is immunologically cross-reactive with human intermediate filament proteins.

Chandrashekar R et al. (1990) Int J Parasitol "Antibody-mediated cytotoxic effects in vitro and in vivo of rat cells on infective larvae of Brugia malayi."

Chandrashekar R, Subrahmanyam D, Rao UR

[Int J Parasitol, 1990]

Albino rat macrophages and neutrophils in the presence of immune serum adhered to and promoted killing of Brugia malayi infective larvae in vitro. At a similar cell-target ratio, macrophages were more potent than neutrophils in inducing cytotoxic response to the larvae. Eosinophils were also effective in killing but only at a high cell-target ratio. The activity in the immune serum could be absorbed to and eluted from a Protein A-Sepharose column suggesting involvement of IgG antibody in the reaction. An indirect fluorescent antibody test confirmed the presence of IgG on the surface of larvae incubated in immune serum. Infective larvae were attacked by host cells within micropore chambers 16-24 h after implantation into immunized rats. Further, a strong cytotoxic response to the larvae was seen when they were introduced intraperitoneally into immune rats indicating the role of antibody and cells in vivo. We suggest that antibody-dependent cellular cytotoxicity may represent an important mechanism of parasite killing in an immune host.

Chandrashekar R et al. (1995) Mol Biochem Parasitol "Molecular characterization of a Brugia malayi intermediate filament protein which is an excretory-secretory product of adult worms."

Weil GJ, Li BW, Chandrashekar R, Curtis KC

[Mol Biochem Parasitol, 1995]

Filarial parasites release macromolecules into their environment both in vitro and in vivo. These excretory-secretory products (E-S) have been studied with respect to function, vaccination potential, pathogenicity, and ability to serve as antigen targets for diagnostic tests. We have recently described monoclonal antibody OV-1 which binds to an intermediate filament in E-S and circulating antigens of Onchocerca volvulus. OV-1 also binds to cross-reactive antigens of Brugia malayi. Therefore, OV-1 was used to immunoscreen a B. malayi adult worm cDNA library in an attempt to clone a homologue (BMIF). BMIF is a 1664-bp full-length transcript which codes for 505 amino acids. BMIF has 95% sequence homology at the amino-acid level to OV1CF, an O. volvulus intermediate filament that was also selected with OV-1, and 75% homology to Ascaris intermediate filament A. Southern blot analysis suggests that BMIF is confined to a single location in the genomic DNA of B. malayi. Antibodies raised to BMIF identified native antigens in immunoblots of B. malayi adult worms, infective larvae and adult E-S. In addition, the antibody also bound to a 60-kDa antigen in immunoblots of poly(ethylene glycol)-precipitated immune complexes in sera from B. malayi infected patients. Localization studies showed that the antigen encoded by BMIF is present in the hypodermis, developing embryos and muscle of adult B. malayi. These studies show that BMIF is an E-S product of B. malayi adult worms which is detectable in sera from patients with brugian filariasis.

Natsuka S et al. (2001) J Biochem "Molecular cloning and expression of Caenorhabditis elegans ERp57-homologue with transglutaminase activity."

Ikura K, Natsuka S, Seki R, Takubo R

[J Biochem, 2001]

Formation of cross-linking between proteins via a gamma-glutamyl-epsilon-lysine residue is an important process in many biological phenomena including apoptosis. Formation of this linkage is catalyzed by the enzyme transglutaminase, which is widely distributed from bacteria to the animal kingdom. The simple multi-cellular organism Caenorhabditis elegans also possesses transglutaminase activity associated with apoptosis [Madi, A. et al. (1998) Eur. J. Biochem. 253, 583-590], but no gene with significant homology to vertebrate or bacterial transglutaminases has been found in the C. elegans genome sequence database. On the other hand, protein disulfide isomerases were recently recognized as a new family of transglutaminases [Chandrashekar, R. et al. (1998) Proc. Natl. Acad. Sci. USA 95, 531-536]. To identify the molecule with transglutaminase activity in C. elegans, we isolated from C. elegans a gene homologous to ERp57, which encodes a protein disulfide isomerase, expressed it in recombinant form, and characterized the transglutaminase and protein disulfide isomerase activities of the resultant protein. The C. elegans ERp57 protein had both enzyme activities, and the transglutaminase activity had similar characteristics to the activity in lysate of the whole worm. These results suggested that the ERp57 homologue was one of the substances with transglutaminase activity in C. elegans.

Mehta K et al. Mol Biochem Parasitol "Transglutaminase-catalyzed incorporation of host proteins in Brugia malayi microfilariae."

Mehta K, Rao UR, Chandrashekar R

[Mol Biochem Parasitol]

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.

Rao UR et al. (1987) Immunol Cell Biol "Complement activation by eggs and microfilariae of filarial parasites."

Rao UR, Subrahmanyam D, Chandrashekar R

[Immunol Cell Biol, 1987]

The complement of fresh normal rat serum was activated by filarial eggs and microfilariae (mf). C3 was deposited on the surface of Litomosoides carinii, Brugia pahangi, Brugia malayi and Dipetalonema viteae as seen by immunofluorescence. Intra-uterine and in vitro-derived mf did not bind C3. In contrast, C3 bound to the blood-derived mf of B. pahangi and B. malayi as well as exsheathed mf of L. carinii and B. malayi. Significant consumption of complement was observed with eggs of all filarial species, as well as sheathed mf of B. pahangi, B. malayi and exsheathed mf of L. carinii and B. malayi. These experiments indicated that complement was activated by filarial parasites via the alternative pathway. The bound complement promoted neutrophil-mediated adherence and cytotoxicity.