J Immunol 2009; 183: 2827
Summary : Ag specific human CD4 (+) memory T lymphocytes have mostly been studied using assays of proliferation in vitro. Intracellular cytokine and ELISPOT assays quantify effector cell populations but barely elicit responses to certain recall Ags that elicit strong proliferative responses, eg , tetanus toxoid, that comprise non-Th1 CD4(+) cells. We have found that culturing whole blood with Ag for 40-48 h induces specific CD4(+) T cells to simultaneously express CD25 and CD134. This new technique readily detects responses to well described CD4(+) T cell recall AGs, including preparations of mycobacteria, CMV, HSV-1, influenza, tetanus toxoid, Candida albicans and streptokinase, as well as HIV-1 peptides, with high specificity. The assay detects much higher levels of Ag-specific cells than intracellular cytokine assays, plus the cells retain viability and can be sorted for in vitro expansion. Furthermore, current in vitro assays for human CD4(+) memory T lymphocytes are too labor –intensive and difficult to standardize for routine diagnostic laboratories, whereas the whole- blood CD-25(+)CD134(+) assay combines simplicity of set-up with a straightforward cell surface flow cytometry readout. In addition to revealing the true extent of Ag-specific human CD4(+) memory T lymphocytes, its greatest use will be as a simple in vitro monitor of CD(+) T cell responses to Ags such as tuberculosis infection or vaccines.
Comment : We still lack a test that will detect TB infection with more sensitivity and specificity than the currently available TST and QFTs.