The QuantiFERON®-TB Gold Plus (QFT-Plus) assay is a test on whole blood; it uses peptides simulating ESAT-6 and CFP-10 proteins to stimulate lymphocytes in whole blood. This assay is produced by QIAGEN and is the fourth generation of QuantiFERON assays. QFT-Plus is a modification of the QFT Gold In-Tube test (QFT-GIT), and was developed to improve sensitivity in immunocompromised subjects and young children. QFT-Plus has four tubes, into each of which 1 mL of whole blood is drawn. One tube contains mitogen and acts as the positive control, one tube contains nothing and acts as the negative control. The third tube (TB1) is the same as the TB antigen tube of QFT-GIT and contains TB-specific antigens (ESAT-6 and CFP-10), while the fourth tube (TB2) has the same antigen mix as TB1, but the peptide lengths differ (short and long) to elicit cell-mediated immune responses from both CD4+ and CD8+ T-lymphocytes (52).
Fig. 3.4. The QuantiFERON-TB Gold Plus (QFT-Plus) kits and tubes
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