Diagnostic Potential of Extant Anti-schistosoma Genus-Specific Monoclonal Antibodies

Abstract

The suitability of five Schistosoma genus-specific monoclonal antibodies (MoAbs) (Sh3/34.10, Sh3/38.2, Sh4/14.3, Sh5/32.30 and Sh5/34.10) in detecting schistosome antigens in infected human and cattle was evaluated. These antibodies were employed in various diagnostic assays to diagnose human and animal schistosomiasis. Extant MoAb secreting hybridoma cells were first propagated in culture to produce the MoAbs. The culture supernatants containing secreted antibodies were analysed by immunodiffusion and the isotypes of the immunoglobulins shown to be IgM (Sh3/34.10, Sh3/38.2, Sh5/32.30 and Sh5/34.10) and IgGl (Sh4/14.3). Gel purified fractions of the MoAbs were utilised in developing dipstick ELISA and micro-plate ELISA in diagnosing schistosomiasis. Also, the suitability of the indirect immunoflourescent Antibody Test (IFAT) was employed to demonstrate anti-schistosoma antibodies in the blood of infected cattle. Three of the antibodies (Sh3/38.2, Sh4/14.3, Sh5/32.30) showed no cross-reactivity with Plasmodium falciparum circum-sporozoite protein (CSP) and crude antigen extract of P. falciparum. However Sh3/34.10 and Sh5/34.10 reacted with the crude antigen extract o f P. falciparum at high antibody concentrations even though the reactivity was abrogated at higher antibody titres. In human schistosomiasis, the diagnostic potential of the MoAbs in detecting schistosome antigens were assessed alongside microscopy and the standard Sh2/15.F urinary schistosomiasis dipstick ELISA developed by researchers at the NMIMR. Out of 74 human subjects from a schistosomiasis endemic area screened for urinary schistosomiasis, 81.1% were microscopically positive for S. haematobium eggs whilst the standard dipstick assay gave prevalence estimate of 87.3%. The sensitivity of this assay was 100% whereas the specificity was 64.7% compared with microscopy as the gold standard test. Dipstick assays utilizing the individual Schistosoma genus-specific monoclonal antibodies estimated prevalences of urinary schistosomiasis between 48.6 and 58.1%. The sensitivities of the assays were however lower (60.0-71.1%) compared with microscopy as the gold standard test. Nonetheless, each of the antibodies showed a high specificity of 100% in detecting S. haematobium urinary antigens. The Schistosoma genus-specific antibodies performed similarly when utilized in dipstick to detect S. mansoni infections. Two assays (IFAT and MoAb-based plate ELISA) were developed to diagnose animal schistosomiasis in cattle. The sensitivities of these assays compared well with microscopy. In determining the prevalence of S. bovis, microscopy gave a prevalence of 53.1% compared with 50.0% determined by IFAT. Micro- plate based ELISA utilizing different Schistosoma genus-specific MoAbs estimated prevalence of S. bovis between 46.9% and 50.0%. These assays were sensitive (ranging from 88.2-94.1%) compared with microscopy as the gold standard test and the specificity was each 100%. In view of the limitations of the microscopical approach the assays provided alternative diagnostic tool in detecting animal schistosomiasis in cattle. The study also demonstrated 3.1% (1/32) prevalence of S. indicum in mixed infection with S. bovis by microscopy. Eleven other cattle parasites eggs were demonstrated by microscopy with prevalence ranging from 3.1-21.9%. There was no evidence of cross-reactivity between the antigens of these parasites and the Schistosoma genus-specific MoAbs utilised. This study revealed the diagnostic potentials of the Schistosoma genus-specific MoAbs in detecting schistosome antigens in both humans and cattle. The development of Schistosoma genus-specific MoAb-based dipstick ELISA for diagnosing schistosomiasis is promising.