p24 Antigen Detection Assay Modified with a Booster Step for Diagnosis and Monitoring of Human Immunodeficiency Virus Type 1 Infection

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Abstract
We modified a p24 antigen enzyme-linked immunosorbent assay as a method for diagnosis and monitoring of human immunodeficiency virus type 1 (HIV-1) subtype E infection. This modified assay is based on the use of preheated immune complex dissociation combined with a booster step using a regular Vironostika HIV-1 p24 antigen assay (bioMerieux) to decrease the lower limit of p24 antigen detection from 10 pg/ml (lower limit achievable when using a regular p24 antigen assay) to 0.5 pg/ml (100 virions/ml) by the new method. The correlation between the values obtained by the HIV-1 RNA (Amplicor HIV-1 Monitor) assay and the p24 antigen assay modified with a booster step antigen assay in 160 frozen plasma samples with known viral load and 80 blind fresh plasma samples by Spearman rank were 0.671 (R2 = 0.450; P < 0.01) and 0.782 (R2 = 0.612; P < 0.01). During antiretroviral treatment, the change of p24 antigen level at ≥0.5 log correlated well with the level of HIV-1 in plasma. In order to improve the early diagnosis of HIV-1 infection in 121 infants born to HIV-1-infected mothers, a heat-denatured plasma p24 antigen assay modified with a booster step was compared with DNA-PCR and HIV RNA (nucleic acid sequence-based amplification) assays. The sensitivity of the antigen test modified with a booster step was similar to that of the HIV-1 RNA (NASBA QL) assay and better than that of the DNA-PCR assay (100 versus 61.90%) for subjects 1 to 2 months old. The overall results from this study might renew interest in p24 antigen detection as an easily affordable alternative method for diagnosis of HIV-1 infection and monitoring of disease progression in developing countries.

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