Performance of indirect immunofluorescence assay, immunochromatography assay and reverse transcription-polymerase chain reaction for detecting human respiratory syncytial virus in nasopharyngeal aspirate samples

Comparison of the use of indirect immunofluorescence assay (IFA), immunochromatography assay (ICA-BD) and reverse transcription-polymerase chain reaction (RT-PCR) for detecting human respiratory syncytial virus (HRSV) in 306 nasopharyngeal aspirates samples (NPA) was performed in order to assess their analytical performance. By comparing the results obtained using ICA-BD with those using IFA, we found relative indices of 85.0 percent for sensitivity and 91.2 percent for specificity, and the positive (PPV) and negative (NPV) predictive values were 85.0 percent and 91.2 percent, respectively. The relative indices for sensitivity and specificity as well as the PPV and NPV for RT-PCR were 98.0 percent, 89.0 percent, 84.0 percent and 99.0 percent, respectively, when compared to the results of IFA. In addition, comparison of the results of ICA-BD and those of RT-PCR yielded relative indices of 79.5 percent for sensitivity and 95.4 percent for specificity, as well as PPV and NPV of 92.9 percent and 86.0 percent, respectively. Although RT-PCR has shown the best performance, the substantial agreement between the ICA-BD and IFA results suggests that ICA-BD, also in addition to being a rapid and facile assay, could be suitable as an alternative diagnostic screening for HRSV infection in children.

Recombinant antigen-based immuno-slot blot method for serodiagnosis of syphilis

Three recombinant antigens of Treponema pallidum Nichols strain were fused with GST, cloned and expressed in Escherichia coli, resulting in high levels of GST-rTp47 and GST-rTp17 expression, and supplementation with arginine tRNA for the AGR codon was needed to obtain GST-rTp15 overexpression. Purified fusion protein yields were 1.9, 1.7 and 5.3 mg/l of cell culture for GST-rTp47, GST-rTp17 and GST-rTp15, respectively. The identities of the antigens obtained were confirmed by automated DNA sequencing using ABI Prism 310 and peptide mapping by Finningan LC/MS. These recombinant antigens were evaluated by immuno-slot blot techniques applied to 137 serum samples from patients with a clinical and laboratory diagnosis of syphilis (61 samples), from healthy blood donors (50 samples), individuals with sexually transmitted disease other than syphilis (3 samples), and from individuals with other spirochetal diseases such as Lyme disease (20 samples) and leptospirosis (3 samples). The assay had sensitivity of 95.1 percent (95 percent CI, 86.1 to 98.7 percent) and a specificity of 94.7 percent (95 percent CI, 87.0 to 98.7 percent); a stronger reactivity was observed with fraction rTp17. The immunoreactivity results showed that fusion recombinant antigens based-immuno-slot blot techniques are suitable for use in diagnostic assays for syphilis.

Antígeno recombinante 47kDa de Treponema pallidum: caracterização imunológica e estudo comparativo com o antígeno nativo / Recombinant Treponema pallidum 47 kDa antigen: immunological characterization and comparative study with native antigen

O antígeno recombinante 47 kDa de Treponema palludum foi caracterizado por SDS-PAGE e immunobiotting (IB) com soro de paciente com diagnóstico da sífilis. NO SDS-PAGE o antígeno recombinante apresentou uma banda de 67 kDa. No IB foram reveladas várias bandas de 87 a 33 kDa, sendo mais expressiva a de 67 kDa. Obteve-se um anticorpo monoespecífico (anti-67 kDa do antígeno recombinante), em eluato com tampão glicina, cuja reatividade foi avaliada com o antígeno nativo – Treponema pallidum. Este reagiu somente com a banda 47 kDa do antígeno nativo e com todas as bandas do antígeno recombinante. No ELISA, o antígeno recombinante falhou na detecção de 3 amostras positivas, os quais apresentaram maior reatividade para as frações 17 e/ou 35 kDa, enquanto uma amostra apresentou baixa reatividade com a fração de 47 kDa, no IB com antígeno nativo. Conclui-se que a proteína múltiplas bandas mantêm a especificidade antigênica, sugerindo que podem ser componentes de polímero ou frações de degradação, algumas amostras positivas não apresentam anticorpos contra o epítopo de 47kDa, tornando questionável o uso deste antígeno para o diagnóstico da sífilis.