Discordant CD38 measurement of CD8+ T lymphocytes using fluorescein conjugates in comparison with phycoerythrin conjugates.

Background: We have previously shown that monitoring of CD38 expression can be used as a marker for antiretroviral drug efficacy in HIV infected patients. However, the detection of CD38 expression may be affected by the sensitivity of the fluorochrome conjugated reagent.

Objective: In this study, we determined the level of CD38 expression using PE and FITC conjugated anti-CD38 monoclonal antibodies in different groups of HIV infected patients.

Methods: The frequency and mean fluorescence intensity of CD38 expression using PE and FITC conjugated anti-CD38 monoclonal antibodies were detected by flow cytometry either alone or in combination with HLA-DR. A correlation between CD38 expression and CD4 count, the percentage of CD4 or viral load in antiretroviral drug naive HIV infected patients was performed. The results were compared with those for antiretroviral treated HIV infected patients who responsed to therapy and patients with virological failure.

Results: We found that while both reagents had the ability to detect a high frequency of CD38 expressing cells in untreated patients, only PE conjugated reagent provided correlation with markers for disease progression. More importantly, FITC conjugated reagent cannot monitor the increase in CD38 expression in patients who showed virological failure.

Conclusions: The results from this study suggest that a cautious selection of fluorochrome conjugated reagents and a method for utilizing the data are extremely critical in the use of CD38 expression as a monitoring tool for ART efficacy.