Identification of Wb123 as an Early and Specific Marker of Wuchereria bancrofti Infection

Abstract

BackgroundThe current antibody tests used for monitoring in lymphatic filariasis (LF) elimination programs suffer from poor specificity because of the considerable geographical overlap with other filarial infections such as Loa loa (Ll), Onchocerca volvulus (Ov), and Mansonella perstans (Mp).MethodsUsing bioinformatics to assemble into contigs 2048 expressed sequence tags (ESTs) from the L3 infective larvae of W. bancrofti (Wb), these were next assessed for homology to known proteins and nucleotides and to similar assemblies of L3 larval ESTs of B. malayi (Bm – n = 5068), Ov (n = 4166), and Ll (n = 3315). Nineteen potential L3- and Wb- and/or Bm-specific antigens were identified. Sixteen of the 19 antigens could be expressed as fusion proteins with Renilla luciferase (Ruc); these were used in a rapid Luciferase Immunopreciptation System (LIPS) assay.ResultsOne of the 16 expressed antigens (Wb123) was both highly immunogenic and specific for Wb. Using Wb123-based IgG and IgG4 LIPS assays on well-defined sera from normal North Americans and those infected exclusively with intestinal helminths, we could detect all of the Wb-infected individuals (from diverse geographic regions) with 100% sensitivity and 100% specificity. Using sera from exclusively Ll-infected, Ov-infected Mp-infected or Bm-infected subjects as the negative comparator, the sensitivities were between 98–100% and the specificities ranged between 84–100% (for IgG anti-Wb123) and between 98–100% (for IgG4 anti-Wb123). Blinded assessments using panels of sera from various Wb-, Bm- or non-Wb helminth-infected subjects demonstrated equally high degrees of sensitivity and specificity.SignificanceWe have identified a Wb-encoded antigen that can be used both as a rapid, high throughput tool to diagnose individual Wb infections and as a sensitive method for early detection of recrudescent infections in areas of control and for mapping new areas of Wb transmission.

Rapid Wuchereria bancrofti-Specific Antigen Wb123-Based IgG4 Immunoassays as Tools for Surveillance following Mass Drug Administration Programs on Lymphatic Filariasis

“…To determine how the Wb123 IgG4 rapid ELISA compares with platforms used in other studies (12)(13)(14)17), subsets of samples previously tested by these methods in this laboratory were compared with the current ELISA results. The primary comparison was to the recently described Wb123-GST LIPS assay (13).…”

“…The primary comparison was to the recently described Wb123-GST LIPS assay (13). Approximately 35% (134/384) of the patients used for the ELISAbased test had previously been tested by the IgG-based LIPS assay.…”

“…Wb123 was originally identified using Brugia malayi and W. bancrofti L3 expressed sequence tags (ESTs) (13) and has a length of 372 amino acids. It most likely belongs to the serpin family of proteins, known to be serine protease inhibitors that are secreted by filaria and highly immunogenic in humans.…”

“…The LIPS assay for detection of both IgG and IgG4 antibodies to Wb123-GST has been described in detail previously (13). Very briefly, sera were diluted 1:10 and added to a Ruc-Wb123 enzyme reporter.…”

“…In addition, while antibody to Bm33 appears earlier than antibodies to the other recombinants tested, it is a highly immunodominant antigen in the filaria and is likely to be very cross-reactive (12). To address the problem of specificity, a recent diagnostic method based on antibodies to the Wuchereria bancrofti antigen Wb123 was developed using a luciferase immunoprecipitation system (LIPS) (13) that has since been further tested in 2 populations in which W. bancrofti is endemic (12,14) and has been shown to precede the appearance of anti-genemia. While the LIPS format showed a very high degree of sensitivity and specificity to Wb123, the expense of new equipment needed for this assay (and some of the nonstandard reagent costs) remains a deterrent to its widespread use.…”