EVALUATION OF CD27 EXPRESSION AS A POTENTIAL BIOMARKER TO DISCRIMINATE ACTIVE FROM LATENT TUBERCULOSIS
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There is no Gold standard test that can be used to differentiate Latent Tuberculosis Infection (LTBI) from Active Tuberculosis (ATB) with the current tests available. We investigate the use of CD27 expression on CD4 T cells as a potential biomarker to differentiate LTBI from ATB. Peripheral Blood Mononuclear Cells (PBMC’s) were obtained from 67 participants of the Kampala TB (KTB) study. We used cells from 19 TB non-infected, 38 LTBI, and 10 ATB. Cells were stained with conjugated monoclonal antibodies and acquired on an LSR II flow cytometer. A set of surface markers were selected to categorize the different CD4 T cells expressing CD27. CD27 expression on naïve and central memory CD4 T cells did not show any significant differences among the different TB stages and therefore it cannot be used to differentiate LTBI from ATB (area under the ROC curve (AUC) of 0.4750 and 0.4132 respectively). There was an increase in the percentage of CD27 expression on CD4 T cells among the ATB. Using a cut off of >=36.6 cells for LTBI, and >=47.8 cells for ATB, naïve cells were able to diagnose LTBI (79% sensitivity) and ATB (50% sensitivity). The search for biomarkers to discriminate LTBI from ATB however remains urgent, but this study has managed to demonstrate the feasibility of using cell surface markers for these nobel purposes.