Performance Evaluation of a Prototype Architect Antibody Assay for Babesia microti.

The tick-borne protozoan Babesia microti is responsible for more than 200 cases of transfusion-transmitted babesiosis (TTB) infection in the United States that have occurred over the last 30 years. Measures to mitigate the risk of TTB include nucleic acid testing (NAT) and B. microti antibody testing. A fully automated prototype B. microti antibody test was developed on the Architect instrument. The specificity was determined to be 99.98% in volunteer blood donors (n = 28,740) from areas considered to have low endemicity for B. microti The sensitivity of the prototype test was studied in experimentally infected macaques; a total of 128 samples were detected as positive whereas 125 were detected as positive with an indirect fluorescent antibody (IFA) test; additionally, 83 (89.2%) of the PCR-positive samples were detected in contrast to 81 (87.1%) using an IFA test. All PCR-positive samples that tested negative in the prototype antibody test were preseroconversion period samples. Following seroconversion, periods of intermittent parasitemia occurred; 17 PCR-negative samples drawn in between PCR-positive bleed dates tested positive both by the prototype test (robust reactivity) and IFA test (marginal reactivity) prior to the administration of therapeutic drugs, indicating that the PCR test failed to detect samples from persistently infected macaques. The prototype assay detected 56 of 58 (96.6%) human subjects diagnosed with clinical babesiosis by both PCR and IFA testing. Overall, the prototype anti-Babesia assay provides a highly sensitive and specific test for the diagnosis of B. microti infection. While PCR is preferred for detection of window-period parasitemia, antibody tests detect infected subjects during periods of low-level parasitemia.

Understanding interactions between immunoassay excipient proteins and surfactants at air-aqueous interface.

Air-aqueous interfacial properties of four excipient proteins commonly used in immunoassay reagent formulations were studied with shear rheology and surface characterization methods. A Du Noüy ring geometry was utilized to quantify the elastic (G') and viscous (G″) shear moduli of protein interfacial networks and to probe the effect of several nonionic surfactants at various concentrations. Time sweep protocols of buffered protein solutions yielded G' in the range of 16 mN/m for bovine serum albumin (BSA), 6 mN/m for bovine gamma globulin (BGG), 7 mN/m for Mouse IgG, and 0.9 mN/m for sodium caseinate. G's were higher than G″s for a given protein. Effect of nonionic surfactants on G' of a protein was concentration dependent and the magnitude of protein displacement from the interface varied with Tween 20>Triton X-100>Triton X-405, with the exception of Mouse IgG. Degree of displacement of BSA from the interface by Tween 20 was approximately 66-fold greater than that of BGG whose displacement by Tween 20 was approximately 7-fold greater than that of Mouse IgG. Degree of displacement by Triton X-100 was comparable in case of studied proteins. Surface tension characterization suggests that the interfacial interactions between proteins and surfactants are driven not only by their surface activity but also by the network formation abilities of the proteins. Data presented here demonstrates a potential application of interfacial studies to sensitively identify discriminatory interactions between proteins and surfactants in immunoassay solutions.