Antibody response to a filarial antigen fraction in individuals exposed to Wuchereria bancrofti infection in India

Increased IgG antibody responses to excretory/secretory antigens in neonates born from mothers infected with filarial nematodes

The present investigation aimed to evaluate the extent to which maternal filarial infection influences IgG subclass immune responses in the cord blood of neonates. Prevalence of antigenaemia was detected using an Og4C3 assay. Filaria-specific IgG subclasses against excretory/secretory antigens were measured by ELISA. Transplacental transfer of circulating filarial antigen (CFA) was observed from 34.8% of CFA-positive mothers to their respective cord bloods. Filaria-specific IgG1, IgG2 and IgG4 responses were significantly higher among cord bloods of infected mothers compared to cord bloods of uninfected mothers. In contrast, the IgG3 response was significantly higher among cord bloods of uninfected mothers. The study shows that transplacental transfer of filarial antigens and filaria-specific IgG4 occurs more in mothers having high worm burdens, and transfer of filaria-specific IgG3 occurs more in the cord blood of uninfected mothers. The findings of the study provide evidence for the development of prenatal sensitization to filarial antigens in utero, and high filaria-specific IgG4 in cord blood may serve as a marker for in-utero sensitization.

In utero sensitization modulates IgG isotype, IFN-γ and IL-10 responses of neonates in bancroftian filariasis

In utero exposure has been considered as a risk factor for filarial infection. To evaluate the influence of maternal infection on filarial-specific IgG subclass response in neonates and their correlation with plasma levels IL-10 and interferon-γ, 145 pairs of mothers and their respective cord bloods were examined. Transplacental transfer of circulating filarial antigen (CFA) was observed in 34·8% cord bloods from CFA positive mothers. Filarial-specific IgG1, IgG2 and IgG4 responses of cord bloods were found to be positively correlated with CFA of mothers. In contrast, IgG3 responses negatively correlated with CFA of mothers. The % of similarity of recognition pattern in the cord blood with maternal blood was high for IgG3 response than IgG4 in all three groups. An increased levels of IL-10 and decreased levels of interferon gamma (IFN-γ) were observed in cord blood of infected mothers. Interferon gamma was positively correlated with IgG3 and negatively correlated with IgG4 level. On the other hand, IL-10 was positively correlated with IgG4 and CFA, indicating that cytokines may play a role in modulating the immune responses in cord bloods of sensitized foetus. The findings of the study reveal that in utero tolerance or sensitization may influence the filarial-specific immunity to infection in neonates.

Biochemical characterization and evaluation of a Brugia malayi small heat shock protein as a vaccine against lymphatic filariasis

Filarial nematodes enjoy one of the longest life spans of any human pathogen due to effective immune evasion strategies developed by the parasite. Among the various immune evasion strategies exhibited by the parasite, Interleukin 10 (IL-10) productions and IL-10 mediated immune suppression has significant negative impact on the host immune system. Recently, we identified a small heat shock protein expressed by Brugia malayi (BmHsp12.6) that can bind to soluble human IL-10 receptor alpha (IL-10R) and activate IL-10 mediated effects in cell lines. In this study we show that the IL-10R binding region of BmHsp12.6 is localized to its N-terminal region. This region has significant sequence similarity to the receptor binding region of human IL-10. In vitro studies confirm that the N-terminal region of BmHsp12.6 (N-BmHsp12.6) has IL-10 like activity and the region containing the alpha crystalline domain and C-terminus of BmHsp12.6 (BmHsp12.6αc) has no IL-10 like activity. However, BmHsp12.6αc contains B cell, T cell and CTL epitopes. Members of the sHSP families are excellent vaccine candidates. Evaluation of sera samples from putatively immune endemic normal (EN) subjects showed IgG1 and IgG3 antibodies against BmHsp12.6αc and these antibodies were involved in the ADCC mediated protection. Subsequent vaccination trials with BmHsp12.6αc in a mouse model using a heterologous prime boost approach showed that 83% protection can be achieved against B. malayi L3 challenge. Results presented in this study thus show that the N-BmHsp12.6 subunit of BmHsp12.6 has immunoregulatory function, whereas, the BmHsp12.6αc subunit of BmHsp12.6 has significant vaccine potential.

Protective efficacy of a filarial surface antigen in experimental filariasis

A water-insoluble, detergent-soluble, surface-associated glycoprotein, designated as Dssd1, was found to induce microfilaria clearance in Mastomys coucha implanted with Setaria digitata. Intraperitoneal implantation of adult female worms of S. digitata in M. coucha could induce microfilaraemia lasting about 165 days in circulation. Immunization of M. coucha with Dssd1 antigen either before or after implantation of worms resulted in a significant reduction in microfilaria density. Complete clearance of circulating microfilaria was achieved by immunization (before and after implantation) in animals by 95 and 105 days post-implantation, respectively, indicating the efficacy of Dssd1 antigen in the clearance of microfilaraemia in infected M. coucha.

Vaccination with 73kDa recombinant heavy chain myosin generates high level of protection against Brugia malayi challenge in jird and mastomys models

We have earlier reported identification, expression and purification of a 2.0kb cDNA clone coding for Brugia malayi heavy chain myosin which exhibited strong immuno-reactivity with bancroftian sera from endemic normal (EN) human subjects which are considered to be putatively immune. In the present study, immunoprophylactic characterization of B. malayi recombinant myosin was carried out in rodent models and the protective efficacy was evaluated by assessing the microfilarial burden and adult worm counts in vaccinated host after an infective larval challenge. Data indicates that immunization resulted in to a significant reduction in microfilarial burden (approximately 76%) and adult worm establishment (54-58%), accompanied with embryostatic effect (70-75%) in both the animal models. The findings suggest that immune-protection by recombinant myosin was conferred through both humoral and cellular arms of immunity as indicated by an increased antibody titer with predominance of IgG2a and IgG2b isotypes along with elevated level of IgG1 apart from significant proliferation of lymphocytes, increased nitric oxide production and profound adherence of splenocytes causing cytotoxicity to microfilariae and infective larvae. The present study indicates that the recombinant B. malayi myosin is a promising vaccine candidate against human lymphatic filarial infection.

Setaria digitata: identification and characterization of a hypodermally expressed SXP/RAL2 protein

SXP-1, an immunodominant filarial protein identified from Wuchereria bancrofti from our centre and previously exploited for diagnosis of human lymphatic filariasis, has been shown to be well conserved across several filarial species. In the present study, we describe the identification of SXP protein from the cattle filarid Setaria digitata using antiserum raised against recombinant WbSXP-1, and were able to detect 34 and 66kDa proteins from the crude protein extracts of S. digitata. These reactive proteins were found to be sheath proteins localized to the hypodermal region of the parasite.

Antigenemia is associated with low antibody response to carbohydrate determinants of a filarial surface antigen

The IgG response to a filarial surface antigen (DssdI) was evaluated in circulating antigen (Og4C3 test) positive and negative individuals from the Wuchereria bancrofti endemic region of Orissa, India. Circulating filarial antigen (CFA) positive individuals exhibited depressed antibody levels to DssdI and individuals with high antibody levels were invariably CFA negative. Low IgG levels to DssdI are associated with CFA positivity irrespective of microfilaraemia and clinical status. Thus asymptomatic microfilaraemic individuals with antigen positivity exhibited low IgG levels similar to symptomatic (chronic filariasis with elephantiasis, hydrocele) or asymptomatic amicrofilaraemic individuals with antigenemia. Western blot analysis revealed a band of approximately 210 kDa reactive with CFA-negative, but not with CFA-positive sera. DssdI was subjected to mild periodate oxidation to investigate the role of carbohydrate epitopes. The treatment considerably reduced the antigenic recognition of DssdI, stressing the immunodominance of carbohydrate residues of DssdI in infection-free individuals. In contrast, individuals with active infection failed to produce such antibodies to filarial surface carbohydrates.

Lymphatic filariasis: new insights into an old disease

Lymphatic filariasis has afflicted people in the tropical areas of the world for thousands of years but even up to comparatively recent times it has been poorly understood and its importance under recognised. In the last 2 decades or so there has been a flurry of activity in filariasis research, which has provided new insights into the global problem of filariasis, the pathogenesis of filarial disease, diagnosis and control.