The Wuchereria bancrofti orthologue of Brugia malayi SXP1 and the diagnosis of bancroftian filariasis

The gene encoding the Wurchereria bancrofti orthologue of the Brugia malayi -derived diagnostic antigen SXP1 was identified from a W. bancrofti L3 cDNA library and characterized. The Wb-sxp-1 cDNA encoded a basic protein with a calculated molecular mass of 20.8 kDa. Wb-SXP-1 was 85% identical to the SXP1 protein described from B. malayi (Bm-SXP-1). The Wb-SXP-1 sequence als o showed significant identify with proteins described from B. pahangi, Onch ocerca volvulus, Acanthochilonema vitea, Ascaris suum, Loa loa, Litomosoide s sigmodontis and Caenorhabditis volvulus. The presence of a number of inva riant and conserved residues in all of these nematode-derived molecules sug gests that Wb-SXP-1 is a member of a new protein family. A recombinant form of Wb-SXP-1 was produced and it was determined that the anti-Wb-SXP-1 anti body response in patients with W. bancrofti infections was restricted to th e IgG4 subclass. An anti-Wb-SXP-1 IgG4 ELISA was developed and this assay w as found to be 100% sensitive for patients with patent W. bancrofti infecti on. Sera from individuals experiencing chronic pathology, endemic normals o l patients with non-filarial nematode infections had no detectable IgG4 aga inst Wb-SXP-1. While patients with patent Onchocerca volvulus infections we re uniformly negative in the Wb-SXP-1 assay, 40% of sera from patent Lon lo a infections were positive. When Bm-SXP-1 was used as the antigen under ide ntical conditions, the assay was 88% specific for patent W. bancrofti infec tions and the antigen was recognized by antibodies from both O. volvulus an d L. loa infections. The results strongly suggested that, for certain diagn ostic filarial antigens, the use of same-species molecules can enhance the specificity of diagnostic tests. (C) 2000 Elsevier Science B.V. All rights reserved.