Evaluation of the effect of freezing PBMC for storage on cytokine expression after <i>in vitro</i> stimulation for 5 days with <i>Mtb</i> antigens.

<p>Comparison of total cytokine expression (IFNγ, TNFα and/or IL-2) of CD3⁺CD4⁺ T cells after stimulation of fresh or thawed cells with PPD (A), HBHA (B) and ESAT-6 (C). Open circles and filled squares represent uninfected controls and latent tuberculosis-infected (LTBI) subjects respectively. Horizontal lines represent median frequency of cytokine-expressing cells of controls (dotted) and LTBI subjects (full). (D) For 10 LTBI subjects, the frequency of cytokine-expressing cells is evaluated as single positive (white), double positive (grey) and triple positive (black) cells based on the combination of expressed cytokines (IFNγ, TNFα and IL-2) for fresh (F) and thawed (T) PBMC stimulated with HBHA. Statistical analysis was by Wilcoxon matched pairs signed rank test. * p<0.05, ** p<0.01.