Use of ELISA based on NcSRS2 of Neospora caninum expressed in Pichia pastoris for diagnosing neosporosis in sheep and dogs / Utilização de um ELISA baseado em NcSRS2 de Neospora caninum expressa em Pichia pastoris para diagnóstico de neosporose em ovinos e cães

Neosporosis is a disease caused by the protozoon Neospora caninum that leads to significant economic losses in many countries. In the present study, we report on use of the recombinant protein NcSRS2 of N. caninum expressed in Pichia pastoris in an indirect immunoenzymatic assay (ELISA) for diagnosing neosporosis infection in sheep and dogs. We observed that the ELISA test yielded specificity of 94.5% and sensitivity of 100% for sheep and specificity of 93.3% and sensitivity of 100% for dogs. We observed that the sensitivity was higher than shown by the indirect fluorescent antibody test, and this was confirmed by means of Western blot. The results from this study suggest that the recombinant protein expressed in P. pastoris is a suitable antigen for use in immunodiagnosis to detect N. caninum in two important species exposed to this parasitosis.

A neosporose é uma doença causada pelo protozoário Neospora caninum que leva a perdas econômicas importantes em muitos países. No presente estudo, é descrita a utilização da proteína recombinante NcSRS2 de N. caninum expressa em Pichia pastoris em um ensaio imunoenzimático indireto (ELISA) para o diagnóstico de infecção por Neospora em ovelhas e cães. Observou-se, que utilizando-se um ELISA, o teste produziu uma especificidade de 94,5% e uma sensibilidade de 100% para ovinos; e uma especificidade de 93,3% e sensibilidade de 100% para cães. Uma maior sensibilidade foi observada em relação à IFI que foi confirmada por Western blot. Os resultados deste estudo sugerem que a proteína recombinante expressa em P. pastoris é bom antígeno para ser utilizado no diagnóstico imunológico para detectar N. caninum em duas espécies importantes expostas a esta parasitose.

Identification of Outer Membrane Vesicles Derived from Orientia tsutsugamushi

Orientia tsutsugamushi, a causative pathogen of Scrub typhus, is a gram-negative intracellular bacterium. Outer membrane vesicles (OMVs) are produced from the membrane of bacteria and play many roles related to the survival of the pathogen. However, there have been no reports confirming whether O. tsutsugamushi indeed produce OMVs. O. tsutsugamushi boryong was cultured in ECV-304 cells for the purification of OMVs. Western blot analysis and immunoenrichment using anti-O. tsutsugamushi monoclonal antibody and electron microscopy were employed for identification and characterization of OMVs. We confirm the presence of OMVs derived from O. tsutsugamushi, and also found that those OMVs contain a major surface antigen of 56-kDa protein and variant immunogenic antigens.

Caracterización de accesiones de papaya (Carica papaya L)a través de marcadores AFLP en Cuba / Characterising Cuban papaya accessions (Carica papaya L) by AFLP markers

Los marcadores moleculares son herramientas valiosas en los estudios genéticos en plantas, y están siendo empleados exitosamente en programas de mejoramiento principalmente en la elección de progenitores y en la selección. El polimorfismo observado mediante la técnica molecular AFLP (Amplified Fragment Length Polymorphism) ha sido de utilidad para estudios de diversidad genética en frutales. En el presente trabajo se realizó la caracterización molecular de 12 accesiones de papaya (Carica papaya L.) del banco de germoplasma del Instituto de Investigaciones en Fruticultura Tropical (IIFT), empleando la técnica AFLP. Se evaluaronseis combinaciones de iniciadores para la amplificación selectiva, las cuales amplificaron un total de 431 bandascon 73,3% de polimorfismo. El número total de patrones de bandas identificados fue igual en todas las combinaciones utilizadas, con un porcentaje de identificación alto, lo que sugiere que dichas combinaciones pudieran ser empleadas para estudios de variabilidad genética en papaya. En general, los resultados presentados demuestran que existe diversidad genética entre las accesiones evaluadas, lo cual constituye un reflejo del origen que presentan los genotipos analizados a partir de la introducción de materiales foráneos y la polinización abierta de un grupo de materiales selectos. Por tanto, se recomienda retomar la prospección y selecciónde accesiones locales, así como la introducción de nuevos genotipos foráneos, como dos vías fundamentalespara aumentar la diversidad genética presente en el banco de germoplasma de papaya de Cuba.

Molecular markers are valuable tools for genetic studies in plants and they are often used successfully in genetic breeding, mainly for choosing progenitors and selection. Polymorphism observed by amplified fragment length polymorphism (AFLP) has been useful for genetic diversity studies in fruit trees. Twelve papaya accessions from the Tropical Fruit Crop Research Institute germplasm bank were molecularly characterised by AFLP. 431 bands having 73.3% polymorphism were obtained using 6 primer combinations. The total number of band patterns identified was the same in all combinations assayed with a high percentage of identification, suggesting that such primer combinations could be used for genetic variability studies in papaya.The results demonstrated genetic diversity among the papaya accessions evaluated, indicating the origin ofthe analysed genotypes from exogenous material and open pollination of a selected group of material. It is thus recommended that local accessions and their selection be monitored as well as the introduction of new foreign genotypes as two ways of increasing the genetic diversity of the Cuban papaya germplasm bank.

Comparison of indirect ELISA based on recombinant protein NcSRS2 and IFAT for detection of Neospora caninum antibodies in sheep / Comparação entre ELISA baseado no antígeno recombinante NcSRS2 e RIFI para detecção de anticorpos de Neospora caninum em ovinos

Neospora caninum, an Apicomplexan parasite that can causes abortion, is responsible for considerable economic and reproductive losses in livestock. The purpose of the present study was to determine whether recombinant NcSRS2 is a suitable indirect ELISA antigen for determining specific immune response to N. caninum in sheep. A total of 441 serum samples were subjected to IFAT and rNcSRS2 based-ELISA, with both tests performing similarly. The sensitivity and specificity of indirect ELISA were 98.6 and 98.3 percent, respectively. The kappa index shows 0.98 concordance between the two tests, which is considered excellent. Seroprevalences of 30.8 and 32.0 percent were detected by IFAT and indirect ELISA, respectively, showing these tests did not differ significantly on this measure (p > 0.05). Serological analysis showed that HisG tag was detected by Western Blotting recognizing rNcSRS2 protein. The potential value of rNcSRS2-based ELISA as a highly specific and sensitive tool for serological diagnosis is also supported by the strong agreement found between IFAT and ELISA. The results support the potential use of recombinant protein NcSRS2 as an antigen in indirect ELISA in sheep.

Neospora caninum é um parasito Apicomplexa que pode causar abortos e é reconhecido como agente importante responsável por perdas econômicas e reprodutivas. Este estudo avaliou a proteína recombinante NcSRS2 como antígeno para ELISA indireto na determinação de resposta imune para N. caninum em ovinos. 441 amostras de soro foram analisadas por IFAT e ELISA indireto com rNcSRS2 e ambos os testes revelaram comportamento similar. A sensibilidade e especificidade de ELISA indireto foram 98,6 e 98,3 por cento, respectivamente. O índice kappa mostrou uma concordância entre os dois testes com valor de 0,98, que é considerado excelente. Prevalências de 30,8 e 32,0 por cento detectadas por IFAT e ELISA indireto, respectivamente, mostraram que os testes não diferiram significativamente nesse aspecto (P > 0.05). A análise sorológica revelou que os anticorpos específicos da cauda de histidina reconheceu por Western Blotting a proteína recombinante NcSRS2. O valor potencial do ELISA indireto baseado no antígeno rNcSRS2 como ferramenta altamente específica e sensível para diagnóstico sorológico é também reforçado pela alta concordância dos valores obtidos com IFAT e com ELISA indireto. Esses resultados respaldam o uso potencial da proteína rNcSRS2 como antígeno em ELISA indireto em ovinos.

Development of a monoclonal antibody-based co-agglutination test to detect enterotoxigenic Escherichia coli isolated from diarrheic neonatal calves

Escherichia coli (E. coli) strains were collected from young diarrheic calves in farms and field. Strains that expressed the K99 (F5) antigen were identified by agglutination tests using reference antibodies to K99 antigen and electron microscopy. The K99 antigen from a selected field strain (SAR-14) was heat-extracted and fractionated on a Sepharose CL-4B column. Further purification was carried out by sodium deoxycholate treatment and/or ion-exchange chromatography. Monoclonal antibodies to purified K99 antigen were produced by the hybridoma technique, and a specific clone, NEK99-5.6.12, was selected for propagation in tissue culture. The antibodies, thus obtained, were affinity-purified, characterized and coated onto Giemsastained Cowan-I strain of Staphylococcus aureus (S. aureus). The antibody-coated S. aureus were used in a coagglutination test to detect K99+ E. coli isolated from feces of diarrheic calves. The specificity of the test was validated against reference monoclonal antibodies used in co-agglutination tests, as well as in ELISA. Specificity of the monoclonal antibodies was also tested against various Gram negative bacteria. The developed antibodies specifically detected purified K99 antigen in immunoblots, as well as K99+ E. coli in ELISA and co-agglutination tests. The co-agglutination test was specific and convenient for large-scale screening of K99+ E. coli isolates.

Utilization of antihepatocyte clone OCH1E5 (Hep Par 1) in histological evaluation of liver tumors.

Diagnosis of hepatocellular carcinoma (HCC) is not always easy on simple hematoxylin and eosin (H&E) stain. The diagnostic problems arise when tumor shows pseudoglandular, pleomorphic or clear cell differentiation. Various tumors markers have been described with varying sensitivity and specificity. Monoclonal antibody Hep Par 1 (OCH1E5) which is specific for hepatocytes offers great help in separation of these tumors. The aim of the present study was to determine utility of Hep Par 1 (OCH1E5) in differentiating HCC from metastatic tumors and cholangiocarcinoma. Total of 62 cases of liver tumors obtained from biopsies, resected or autopsy specimens were included in the study. Slides having representative sections were subjected to immunohistochemistry with monoclonal antibody Hep Par 1 (Dako Corp) using avidin biotin technique with primary antibody dilution of 1:40. Adjacent nontumorous hepatocytes were taken as positive control. Slides were examined by experienced pathologist without any information of clinical or H&E diagnosis. Cases were considered positive for Hep Par 1 if tumor cells showed cytoplasmic brown colored granules. The intensity and distribution (diffuse/ focal) of immunoreactivity was noted. Subsequently immunohistochemistry results were correlated with histology and clinical diagnosis. Hep Par 1 antibody was positive in 26 (42 %) and negative in 36 (58 %) liver tumors. On correlating with H&E sections, out of 26 positive cases, 25 (89.2%) were HCC and one was the case of metastasis of mucin secreting adenocarcinoma. From 36 tumors with negative staining 3 were cases of HCC, 27 metastatic adenocarcinomas and 6 cholangiocarcinomas. Only one case of liver metastasis of mucin secreting adenocarcinoma showed positivity. None of the cases of cholangiocarcinoma showed positivity for Hep Par 1. The three HCCs which did not take up staining for Hep Par 1 were 2 cases of moderately differentiated HCC having pseudoglandular pattern and a case of well differentiated HCC with trabecular arrangement. In 11(44%) cases staining was diffuse while in 14 (56%) it was focal but intense. Hep Par 1 is a useful marker in differentiating HCC from metastaic tumors and cholangiocarcinoma with sensitivity and specificity of 89 % and 97 % respectively and positive predictive value of 96 %. However one should be aware of limitations of immunohistochemistry.

IgE expression on the surface of B1 and B2 lymphocytes in experimental murine schistosomiasis

In a previous study we monitored the distribution and phenotype expression of B1 cells during the evolution of experimental murine schistosomiasis mansoni and we proposed that the B1 cells were heterogeneous: a fraction which originated in the spleen and followed the migratory pathway to mesenteric ganglia, while the other was the resident peritoneal B1-cell pool. In the present study, we have addressed the question of whether these two B1-lymphocyte populations are involved in the production of the late Ig isotype IgE, which is present in high levels in schistosomal infection. Lymphocyte expression of surface markers and immunoglobulins were monitored by immunofluorescence flow cytometry. Both in the spleen and mesenteric ganglia, the B1 and B2 cells were induced to switch from IgM to IgE in the early Th2-dominated phase of the disease, with an increase of IgE in its later phases. Conversely, peritoneal B1-IgM+ switched to the remaining IgE+ present in high numbers in the peritoneal cavity throughout the disease. We correlated the efficient induction of the expression of late Ig isotypes by B1 cells with high levels of inflammatory cytokines due to the intense host response to the presence of worms and their eggs in the abdominal cavity. In conclusion, B1 cells have a different switch behavior from IgM to IgE indicating that these cell sub-populations depend on the microenvironment.

Flow cytometry as a tool to identify Mycobacterium tuberculosis interaction with the immune system and drug susceptibility

Flow cytometric analysis is a useful and widely employed tool to identify immunological alterations caused by different microorganisms, including Mycobacterium tuberculosis. However, this tool can be used for several others analysis. We will discuss some applications for flow cytometry to the study of M. tuberculosis, mainly on cell surface antigens, mycobacterial secreted proteins, their interaction with the immune system using inflammatory cells recovered from peripheral blood, alveolar and pleura spaces and the influence of M. tuberculosis on apoptosis, and finally the rapid determination of drug susceptibility. All of these examples highlight the usefulness of flow cytometry in the study of M. tuber-culosis infection.

Trypanosoma cruzi: amastigote polymorphism defined by monoclonal antibodies

We have raised monoclonal antibodies (mAbs) directed towards amastigote forms of Trypanosoma cruzi, and shown that mAbs 1D9 and 4B9 are carbohydrate while mAb 4B5 activity is resistant to periodate oxidation of the antigen. Here we used an ELISA to quantitate and compare the expression of surface epitopes on fixed parasites among different parasite isolates. The expression of markers varied among T. cruzi amastigotes isolated from infected cells or after extracellular differentiation of trypomastigotes. Moreover, we also observed an extensive polymorphic expression of these epitopes among amastigotes derived from different strains and clones. For instance, mAb 2C2 strongly and evenly reacted with 9 strains and clones (G, Y, CL, Tulahuen, MD, and F, and clones Sylvio X-10/4, D11, and CL.B), with absorbance at 492 nm (A492 nm) from 0.6 to 0.8. By contrast, mAb 4B5 had a higher expression in Tulahuen amastigotes (around 0.9 at 492 nm) whereas its reactivity with amastigotes from clones CL.B, Sylvio X-10/4 and D11 was much lower (around 0.4). mAb 1D9 displayed an interesting pattern of reactivity with amastigotes of the different strains and clones (A492 nm of G>D11ÝSylvio X-10/4 = MD>Tulahuen = F = Y>CL>CL.B). Finally, we observed that mAb 4B9 had the lowest reaction with the parasites studied, with higher values of A492 nm with Y strain (around 0.6) and lower values with Tulahuen, F and CL.B strains (around 0.2). Immunoblotting analysis also showed extensive variations among amastigotes of the various parasite isolates and mAbs 4B9, 1D9 and 4B5 revealed significant differences in expression between clones and parental strains. These data describe a previously uncharacterized polymorphism of T. cruzi amastigote surface components

Vaccination of different strains of mice against cutaneous leishmaniosis: Usefulnes of membrane antigens encapsulated into liposomes by intraperitoneal and subcutaneous administration

The objetive of this study was to assess the usefulness of parasite-surfase molecules reconstituted into liposomes to vaccinate four diffeent strains of mice (C57BL/10, CBA/ca, C57BL/6 and NZB) with different levels of susceptibility to L. m. mexicana infection and to find out possible increases in specific antibody response after vaccination. but before infection with virulent promastigotes. Mice were vaccinated with parasite membrane antigens incorporated into liposomes and antibody levels were recorded. Vaccination was effective to protect CBA/ca and C57BL/6 but not C57BL/10 mice and NZB animals were naturally resistant. Intraperitoneal (ip) was more efective than the subcutaneus (sc) route if inoculation, and the induction of disease-resistance correlated with the production of IgG anti-Leishmania in CBA/ca, C57BL/6 and C57BL/10 mice

Monoclonal antibody-based ELISA for the detection of circulating Entamoeba histolytica antigen in hepatic amebiasis in hamsters (Mesocricetus auratus).

Circulating amebic antigens were determined by using a sandwich ELISA with specific monoclonal antibody in the sera of 35 group I hamsters, 7 of which were sacrificed at intervals after hepatic inoculation with 500,000 axenically grown HM:1:IMSS strain of E. histolytica trophozoites, 7 group II infected hamsters in which metronidazole treatment was given and 18 group III uninfected controls. Amebic antigenemia was demonstrated in 5 of 7 (71.4%), 6 of 7 (85.7%), 7 of 7 (100%), 7 of 7 (100%) and 7 of 7 (100%) of group I hamsters on days 5, 10, 15, 20 and 30 of infections respectively, whereas 6 of 7 (85.7%) of group II hamsters were weakly positive, one was negative and all 18 group III hamsters were negative. The sensitivity of the assay was 100% after the animals were infected 15 days onwards. The level of antigenemia in hamsters of group I with abscess was significantly higher than those of the same group without abscess (p < 0.05). Absence or reduction of antigenemia after treatment could be interpreted to mean a positive test of cure and favorable therapeutic response. The MAb-PAb-based ELISA for the detection of circulating E. histolytica represents a simple and sensitive diagnostic test for invasive amebiasis in hamsters. Application of this test in amebic liver abscess patients should be of diagnostic value for indication of present infection or test of cure after successful treatment.

Survivability and leucocyte migration inhibition in mice immunized with cryotreated ascites fibrosarcoma cells using different freeze-thaw cycles.

Attempts have been made to assess as to what extent in vitro assay of cellular immunity, e.g. leucocyte migration inhibition (LMI) in mice immunized with different freeze-thaw cycles could reflect host resistance in vivo. While survivability of animals improved significantly by immunization with single cycle (P < 0.05) to three cycle (P < 0.001) and programmed three cycle (P < 0.001) cryo-treated tumor cells compared to controls, the percentage LMI in the same groups of animals decreased progressively. The KCl(3M) extracted tumor cell protein (antigen) of both viable and cryo-treated cells showed a progressively increased protein concentrations per 1 x 10(6) tumor cells with viable cells being least and programmed three cycle cryo-treated cells highest. The apparent discrepancy observed between percentage migration inhibition and survivability may be due to the fact that (1) survivability is a function of body's total immune response while LMI represents the response of one effector limb only; (2) immuno-regulatory mechanisms depend on a balance between activation and suppression and suppressor cells being more sensitive and of shorter life span, affect migration inhibition but not the survivability; (3) cryo-treatment alters tumor cell surface antigen affecting immunological balance; and (4) suppressor and antitumor activities against antigenic stimulation develop simultaneously in different organs and LMI performed with sensitized splenic cells, where, perhaps, suppressor cell activity dominates.

Dynamics of natural antibody responses to malaria parasite surface proteins in the intermediate rainfall zone of Sri Lanka.

Antibodies against repetitive epitopes on Plasmodium falciparum and P. vivax circumsporozoite (CS) proteins and epitopes on the 45 kDa and 185-200 kDa P. falciparum merozoite surface proteins were measured by radioimmunoassay in a two year longitudinal study in Nikawehera village located in the intermediate rainfall zone of Sri Lanka. The prevalence and concentrations of specific antibodies were in many, but not all instances, greater in adults than in children who were aged 7-15 yr at the beginning of the study. The concentrations and prevalence of antibodies were associated with malaria transmission levels previously determined from entomological and hospital admission data in the area. Antibody responses to epitopes on different P. falciparum antigens, two different epitopes within the 185-200 kDa merozoite surface protein and between the P. falciparum and P. vivax CS repeats were significantly correlated. Antibody concentrations against a conserved epitope in the 185-200 kDa protein were significantly higher in P. falciparum infected individuals than in non-parasitaemic subjects. Antibody concentration and prevalences in Nikawehera were lower than at Weheragala, a site located 70 km away in the dry zone of Sri Lanka. It is postulated that lower levels of immunity in the population in areas such as Nikawehera, that are adjacent to more highly malaria endemic areas, may promote epidemics when conditions favour transmission.

La caracterización de los antígenos de superficie del nemátodo parásito Trichinella spiralis: estudio de su participación en los mecanismos de protección y su utilidad en el diagnóstico de la triquinosis / Charaterization of surface antigens of the parasite nematode Trichinella spiralis: mechanisms of protection and use in diagnosis of trichinosis

Entre los aspectos más importantes en el estudio de la triquinosis, se encuentra el desarrollo de los métodos de diagnóstico específicos y confiables que permitan la detección oportuna de la infección, así como la identificación y caracterización de antígenos del parásito que previenen la infección. En este contexto, la caracterización de los antígenos de superficie esticosoma y de excreción secreción de la larva muscular de Trichinella spiralis, ha sido muy relevante, dada su alta inmunogenicidad prácticamente en todos los huéspedes hasta ahora estudiados. Así, durante el desarrollo de este trabajo se ha logrado identificar y caracterizar las moléculas de estos dos compartimentos de la larva muscular de T. spiralis que se han empleado tanto en la detección específica de la infección por T. spiralis (particularmente en cerdos), como en los ensayos para evaluar su potencial en la inducción de protección modelos murinos

Humoral immune response anti K99 pilus from enterotoxigenic Escherichia coli in experimentally inoculated calves

The bovine model is extremely interesting to study several basic aspects of mucosal local immunity. Many reports have shown that, in young calves, the infectivity of enterotoxigenic Escherichia coli may be inhibited by passively administered antibodies anti K99 pilus. We have measured, by immunoradiometric assays, the IgG response anti K99 pilus in the serum of calves, deprived of colostrum and orally inoculated with enteropathogenic K99+ E. coli. Although variable levels of IgG anti K99 pilus were detected, their protective value could not be ascertained in vivo due to the acute development of the infection. In an effort to correlate the presence of serum antibodies anti K99 pilus with their protective capacity, an ex-vivo assay to monitor the interaction of radiolabeled K99 pilus with the bovine mucosa was standardized. Paradoxically, although K99 pilus, purified by standard procedures, was recognized by polyclonal rabbit and calf antisera, its interaction with the bovine intestinal mucosa, quantitated in the ex-vivo system, was not inhibited by these reagents, indicating that the antibodies did not effectively block those K99 pilus domains involved in the interaction with mucosal receptors

Conceptos actuales en hepatitis por virus B (VHB) y virus C (VHC) / Contemporary concepts on hepatitis due to virus B (VHB) and virus C (VHC)

Los conocimientos que en materia de hepatitis viral se han obtenido en los últimos veinte años son impresionantes, lo cual nos ha permitido conocer con más precisión la historia natural de la enfermedad, la etiopatogenia, el cuadro clínico, el tratamiento y hasta la prevención. Los estudios de tamizaje a las sangres de donadores ha permitido disminuir notablemente la transmisión de la hepatitis viral tipo B que se adquiría por la vía transfusional. Sin embargo, la carencia de marcadores serológicos para prevenir la transmisión por la sangre de la hepatitis no-A, no-B, que recientemente conocemos como hepatitis C, explica el porqué la mayor parte de las hepatitis postransfusión en la actualidad son debidas al virus C. En esta revisión se pretende destacar los aspectos más relevantes de la biología de los virus B y C, así como las implicaciones que en la clínica pueden tener, destacando lo complejo pero fascinante que resulta el estudio de microorganismos que son capaces de desequilibrar al organismo humano, llevándolo incluso hasta la muerte

A longitudinal study of seroreactivities to a major blood stage antigen (Pf155/RESA) of the malaria parasite Plasmodium falciparum in an endemic area of Thailand.

We have performed a longitudinal study of the formation of antibodies to Plasmodium falciparum in an area of Thailand where malaria transmission is moderate and seasonal. The study population comprised 118 subjects living in two villages 230 km southeast of Bangkok. All subjects included in this study were seropositive for antibodies to the blood stages of P. falciparum but only approximately 80% had antibodies to the blood stage antigen Pf155/RESA when assayed by erythrocyte membrane immunofluorescence (EMIF) or peptide ELISA during the period of maximal transmission. The reduced capacity to form these antibodies in a significant fraction of subjects living under comparable environmental and socio-economic conditions may reflect a genetic but antigen specific non-responsiveness. Both seropositivity and mean antibody titers to Pf155/RESA and its B-cell epitopes tended to be slightly higher during the rainy than during the dry season but the seasonal variations were slight and statistically not significant. Parasite rates were significantly higher in the rainy than in the dry season in both the EMIF positive and the EMIF negative groups. However, during the rainy season, the parasite rates in subjects with no or low titered antibodies to Pf155/RESA were significantly higher than those in subjects having such antibodies. The results suggest that antibodies to Pf155/RESA and some of its defined epitopes may be of importance for controlling parasitemias.

Ontogenetic transformation of surface epitope expression, an adaptive immunoevasive strategy of filarial parasites.

Filarial nematodes are highly successful in invading, persisting and propagating in human body and eliciting severe ailments. The exact mechanism by which, filarial nematodes evade the host immunity is still ill-defined. The present investigation on the surface antigens of S. digitata revealed the occurrence of shared antigens in the egg, embryo, mf and adult stages. All these stages showed exposed carbohydrate moieties on their surface. In situ localization studies proved that the egg and embryo have exposed surface epitopes whereas the microfilariae and adults did not have any such epitopes. Based on these observations, a model has been proposed on "the surface epitope hiding", as an immunoevasive strategy of the filarial parasite which explains why the naturally shed surface antigens evoke antifilarial immune response in the host even though the system could not recognize the microfilariae or adult parasite due to lack of exposed surface epitopes, permitting the parasite to escape successfully from immune rejection. As treatment with detergents leads to exposure of surface epitopes of parasites, a safe intervention of parasite surface would be an effective strategy for detection and ultimate control of filariasis.