Cloning, over-expression and evaluation of a recombinant fusion protein of Wuchereria bancrofti towards its application as a diagnostic agent for bancroftian filariasis

Recombinant antigen-based antibody assays for the diagnosis and surveillance of lymphatic filariasis - a multicenter trial

The development of antifilarial antibody responses is a characteristic feature of infection with filarial parasites. It should be possible to exploit this fact to develop tools to monitor the progress of the global program to eliminate lymphatic filariasis (LF); however, assays based on parasite extracts suffer from a number of limitations, including the paucity of parasite material, the difficulty of assay standardization and problems with assay specificity. In principle, assays based on recombinant filarial antigens should address these limitations and provide useful tools for diagnosis and surveillance of LF. The present multicenter study was designed to compare the performance of antibody assays for filariasis based on recombinant antigens Bm14, WbSXP, and BmR1. Coded serum specimens were distributed to five participating laboratories where assays for each antigen were conducted in parallel. Assays based on Bm14, WbSXP, or BmR1 demonstrated good sensitivity (>90%) for field use and none of the assays demonstrated reactivity with specimens from persons with non-filarial helminth infections. Limitations of the assays are discussed. Well-designed field studies are now needed to assess sampling methodology and the application of antibody testing to the monitoring and surveillance of LF elimination programs.

Diagnosis of Wuchereria bancrofti infection by the polymerase chain reaction using urine and day blood samples from amicrofilaraemic patients

A sensitive and specific polymerase chain reaction (PCR) based on a highly repeated deoxyribonucleic acid (DNA) sequence (188 bp; SspI repeat) was tested for the detection of Wuchereria bancrofti DNA in blood and urine samples collected during the day from individuals in Coque, Recife, Brazil, an endemic area for W. bancrofti. All microfilaraemic individuals were also positive by PCR, irrespective of the samples used. The PCR system was capable of detecting W. bancrofti DNA in amicrofilaraemic individuals: c. 93% were positive by PCR when day blood samples were used and 59.7% when urine samples collected at 07:00 were used. Thus, nocturnally periodic W. bancrofti infection can be detected in blood samples collected during the day, which is convenient for large-scale screening. In addition, non-invasive urine collection provided suitable samples for PCR, which is clearly advantageous for preliminary mass diagnosis.

Quantitative assessment of circulating antigens in human lymphatic filariasis: a field evaluation of monoclonal antibody-based ELISA using blood collected on filter strips

OBJECTIVE

To quantify circulating antigens in individuals with lymphatic filariasis by means of an ELISA using blood on filter strips.

METHOD

Circulating antigens in filarial patients and normal individuals living in an area endemic for W. bancrofti infection in Madras, India were estimated using a monoclonal antibody-based ELISA.

RESULTS

All microfilaraemics showed positivity to circulating antigens whereas people with chronic pathology and 80% of the endemic normals tested negative. The antigen levels in the blood collected in the night and during day time showed positivity and there was no difference in the antigen concentration. The results of the antigen levels collected onto filter strips correlated with their corresponding plasma antigen levels (r = 0.83). In microfilaraemics, DEC treatment did not alter the levels of circulating antigens for up to one month.

CONCLUSIONS

We conclude that this monoclonal antibody-based ELISA using filter strips may be used in day time and replace the existing routine night blood surveys in our endemic area in India.

Immunodiagnosis of human lymphatic filariasis: A review

A monoclonal antibody-based antigen detection system was used to detect the levels of circulating antigen in filarial patients before and after treatment with DEC and in normal individuals living in an area endemic forW. bancrofti infection in Chennai, India. The present study was to show the use of this assay as a means of efficient screening for filariásis in an endemic area where blood was absorbed onto the filter paper by finger prick during day time. The results of the antigen levels collected onto filter strips correlated with their corresponding plasma antigen levels (r=0.83). In microfilaraemics, DEC treatment did not alter the levels of circulating antigens upto a period of one month. We conclude that this monoclonal antibody based ELISA using filter strips may be used in daytime and can replace the existing routine night blood survey.

Modulation of cellular immune response by cytokines in bancroftian filariasis

Human lymphatic filariasis is a chronic helminth infection caused byWuchereria bancrofti andBrugia malayi. Wide spectrum of clinical manifestations are seen in different clinical groups of filariasis patients which comprises asymptomatic patients with circulating microfilaria (MF), individuals with chronic lymphatic obstruction (CP), Endemic normals (EN) who are asymptomatic and amicrofilaraemic or the relatively rare tropical pulmonary eosinophilia (TPE). The cellular immune response to this infection varies in different clinical groups of filarial patients. ranging from normal lymphocyte proliferative response in EN individuals to lymphocyte hyporesponsiveness in MF to total parasite antigen [Brugia malayi antigen (BMA)]. But in response to recombinant filarial antigen (pRJ51) the lymphocyte proliferation is restored in MF patients. Interestingly the lymphocytes from MFs responded normally to parasite antigen when EN serum was added in the culture whereas sera from MFs failed to revert the lymphocyte hyporesponsiveness. In order to study the molecular mechanisms responsible for parasite antigen specific lymphocyte hyporesponsiveness, we analysed both the Th1 and Th2 type cytokine gene expression profile in different clinical groups of filarasis patients. MF individuals expressed elevated Th2 type cytokines like IL-4, IL-5 and IL-10 and decreased levels of IL-2 and IFN-γ in response to parasite antigen. Chronic patients have elevated levels of both Th1 and Th2 type cytokines in response to parasite antigen. The EN individuals had a purely Th1 type pattern with absence of IL-4 and IL-5 expression. These studies clearly demonstrate the role of Th2 cytokine like IL-10 in antigen specific hyporesponsiveness seen in MF patients. Any methods to arrest the progression of this disease should concentrate on the means to revert the Th2 type into Th1 type response in the MF patients either by Th1 type cytokine therapy or by using recombinant filarial antigen which stimulates the Th1 response. Further the recombinant filarial antigen which induces Th1 type cytokine response could be used for immunoprophylactic studies.

Cellular immune response studies in bancroftian filariasis

An attempt was made to identify the filarial specific antigens that are capable of inducing immune response in human filariasis. Lymphocytes were taken from three clinically defined groups living in an endemic area in Madras, namely microfilaraemic (MF) subjects with microfilariae in their blood smear without any clinical symptoms, chronic pathology (CP) individuals with lymphangitis or lymphadenitis in combination with a history of recurrent filarial fevers or lymphoedema, and endemic normals (EN) subjects without microfilariae nor any clinical symptoms of pathology. Lymphocytes from the three groups responded with no significant difference (P = 0.21) in their proliferative index to PPD and PHA, although lymphocytes from MF individuals showed significantly (P < 0.001) less proliferative index to Brugia malayi antigen (BMA) than the CP and EN subjects. This antigen specific cellular unresponsiveness seen in MF patients was not reversed by the addition of recombinant IL-1alpha, IL-1beta, and IFN-gamma, but the addition of sera from EN individuals seemed to restore this unresponsiveness (P < 0.001). The peripheral blood mononuclear cells from MF patients secreted more IL-1 in response to BMA induction than the same from CP and EN individuals. A 58 kDa recombinant protein isolated from a Wuchereria bancrofti genomic library (58 kDa) had mounted a higher proliferative response to lymphocytes from all three groups compared to BMA (P < 0.001) indicating the possible use of recombinant filarial protein to mount immunological responses in filarial patients.

Wuchereria bancrofti recombinant antigen-derived poly- and monoclonal antibodies for the detection of circulating antigen(s) in the sera of lymphatic filarial patients

A sandwich antibody ELISA was employed for the detection of circulating filarial antigen in patients with bancroftian filariasis. Wuchereria bancrofti recombinant antigen-derived polyclonal and monoclonal antibodies were successfully used as the revealing antibodies and their efficiency was compared. All the microfilariae (mf) positive (by finger prick and examination of 20 microliters of blood under the microscope) individuals tested showed the presence of circulating antigen(s). Among the antigen positive endemic normals (mf negative by the finger prick method), 43% showed microfilariae by a sensitive parasitological method viz. membrane filtration of the night blood samples. A significant correlation was observed between the parasite antigen levels and the blood microfilaria counts among the mf carriers. This information on the parasite antigen levels could be an ideal monitor to indicate the degree of active infection and in the follow up of chemotherapy.

Immunoglobulin G subclass responses of children during infection with Onchocerca volvulus

To characterize the patterns of immunoglobulin G (IgG) subclass and IgE reactivity during the early stages of onchocerciasis, sera were collected from 224 children (age groups, 2 to 5, 6 to 10, and 11 to 15 years) residing in a region of Sierra Leone where Onchocerca volvulus is endemic, and these samples were tested by enzyme-linked immunosorbent assay for their reactivity to adult antigens (OvAg) and against four recombinant proteins (OV11, OV27, OV29, and OV16). Over 88% of the samples contained detectable levels of anti-OvAg IgG. In samples from microfilaria (MF)-positive children, IgG4 responses were significantly elevated and constituted on average 39, 35 and 28% of the total IgG responses for the age groups of 2 to 5, 6 to 10, and 11 to 15 years, respectively. For MF-negative individuals, the mean contributions of IgG4 to the total IgG response were 11% (2 to 5 years), 27% (6 to 10 years), and 56% (11 to 15 years). OvAg-specific IgE was detectable in the sera from both MF-negative and MF-positive individuals. To increase the specificity of the response, recombinant antigens OV11, OV27, and OV29 were tested individually or as a cocktail. Nearly 50% of the MF-negative children and 85% of the MF-positive children had detectable levels of IgG against at least one of the recombinant antigens. Only a small portion of the IgG against the recombinant peptides was IgG4. The prevalence of IgG against OV16 in samples from MF-negative children was 51%, and that for MF-positive children was 75%. The general profile of the humoral immune responses mounted by both MF-positive and a large percentage of the MF-negative children during the initial phases of infection with O. volvulus is similar to the profile reported for adults harboring chronic O. volvulus infections. These results suggest that very quickly after infection, the interactions between parasite and host result in an immunological environment that may contribute to the maintenance of a long-term, chronic infection.

Vectors to facilitate the creation of translational fusions to the maltose-binding protein of Escherichia coli

A set of vectors has been constructed to facilitate the fusion of heterologous sequences to the C terminus of the maltose-binding protein (MBP) of Escherichia coli. The plasmids carry a cloning region comprising two blunt cloning sites, a BamHI site and multiple stop codons, and this has been placed in each reading frame so that translational fusions to MBP can be generated and manipulated with ease. To demonstrate the utility of this system, recombinant proteins have been engineered in which staphylococcal enterotoxin A has been fused to MBP.

Molecular cloning of Brugia malayi antigens for diagnosis of lymphatic filariasis

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.