doi:10.1016/j.bmc.2008.06.038
Copyright © 2008 Elsevier Ltd All rights reserved.
Major sperm protein as a diagnostic antigen for onchocerciasis
aDepartments of Chemistry and Immunology, The Skaggs Institute for Chemical Biology and Worm Institute for Research and Medicine (WIRM), The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
Received 4 June 2008;
revised 19 June 2008;
accepted 20 June 2008.
Available online 25 June 2008.
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Abstract
Onchocerciasis, also known as river blindness, is the second leading infectious cause of blindness worldwide. In order to successfully control this disease, the development of efficient diagnostic tools as well as effective treatments is imperative. A number of proteins have been proposed as vaccine and diagnostic candidates, yet none have been successfully advanced to the point of general clinical use. We have prepared major sperm protein 2 (MSP2) from Onchocerca volvulus as a possible diagnostic antigen for onchocerciasis. Importantly, recombinant MSP2 is dimeric in solution, identical to α-MSP from the roundworm, Ascaris suum. A panel of sera obtained from Cameroonian individuals afflicted with onchocerciasis positively responded to the recombinant MSP2. Our data suggest that MSP2, like the previously described antigen Ov16, can be utilized as a diagnostic onchocerciasis antigen for monitoring the interruption of transmission.
Keywords: Onchocerciasis; River blindness; Major sperm protein; Immunoassay; Diagnostic
Figure 1. (A) SDS–polyacrylamide gel electrophoresis of the purified MSP2s. 1, marker (Bio-Rad); 2, MSP2-His6; 3, MSP2 after gel filtration chromatography; 4, MSP2 after SP cation exchange chromatography. (B) Analytical gel filtration analysis.
MSP2, Ve = 59.0 mL;
MSP2-His6, Ve = 70.4 mL. (C) Molecular weight calibration curve. Protein standards, albumin (67 kDa, Ve = 44.25 mL, Kav = 0.01), ovalbumin (43 kDa, Ve = 49.75 mL, Kav = 0.083), chymotrypsinogen A (25 kDa, Ve = 62.5 mL, Kav = 0.249), and ribonuclease A (13.7 kDa, Ve = 70.7 mL, Kav = 0.356) were used to generate calibration curve. Apparent molecular mass (Kav) was calculated by the equation, Kav = (Ve − Vo)/(Vt − Vo). See Section 3 for full details.
Figure 2. Dot-blot assay to detect MSP2-specific antibodies in human serum. (A) Twelve samples, six controls (upper panel) and six patients (lower panel), were tested at the same time using a 12-well tissue culture plate. Control 3 indicates a false-positive signal. See Section 3 for full details. (B) No signal was detected with up to 120 μg BSA. All onchocerciasis patient sera showed positive signals, and
14% false-positive signal was detected from skin snip negative controls and LF patients.