Why is it necessary to include a mitogen control in the Quantiferon-Gold assay?

Question

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Topic at hand is the purpose of including a mitogen control in the Quantiferon-Gold assay, a diagnostic tool used to assess cell-mediated immunity by measuring IFN-γ release.
Option 1: 'Mycobacteria stimulate mitogen-responsive T cells' This statement confuses the role of the test antigens with the control. While the assay uses Mycobacterium tuberculosis–derived antigens to stimulate T cells, the mitogen control itself is a non-specific stimulant, not the specific antigen used to detect infection. The option misattributes the source of stimulation to the mitogen control rather than to the test antigens.
Option 2: 'The mitogen control allows comparison of multiple assays performed in the same laboratory' In practice, the mitogen control is not primarily about cross-assay comparability. It serves as a functional readout of T cell capability in the tested sample, rather than a normalization or inter-assay comparison tool. This makes the statement misleading about the control’s main purpose.
Option 3: 'Mitogens stimulate all T cells irrespective of antigen specificity' While it is true that mitogens broadly activate T cells, the core issue in this context is not the breadth of stimulation but whether the T cells are viable and responsive in the assay setup. This option describes a general effect of mitogens but does not address the essential reason for including the control in the QFT assay, which is to verify cellular responsiveness.
Option 4: 'A response to mitogen indicates that the T cells are alive and the assay can be properly interpreted' This statement captures the key rationale: the mitogen control tests whether the patient’s T cells are alive and capable of mounting a response. A positive mitogen control ensures that a negative result for the TB-specific antigens is interpretable as a true negative rather than as a non-responsive sample due to an immune deficiency or technical failure. Conversely, a lack of response to mitogen would cast doubt on the assay result and may indicate an inability to mount an immune response, requiring retesting or alternative interpretation.

MIMI2002 (ND) Immunology Practical Quiz

Why is it necessary to include a mitogen control in the Quantiferon-Gold assay?

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