Assessing cell-mediated immunity (CMI) Which of the following laboratory or clinical methods can be used to detect or evaluate T-cell–mediated (cell-mediated) immune responses in humans?

Introduction / Context:Cell-mediated immunity (CMI) encompasses T-cell effector functions such as delayed-type hypersensitivity, macrophage activation, and cytotoxic T-lymphocyte (CTL)–mediated lysis. Measuring CMI is important in diagnosing infections, immune deficiencies, and vaccine take.

Given Data / Assumptions:

• CMI testing focuses on T-cell–dependent reactions.
• Both in vivo and in vitro methods exist.
• Humoral assays alone do not directly reflect CMI.

Concept / Approach:Migration inhibition assays measure lymphokine-mediated suppression of leukocyte migration. CTL assays quantify target cell killing by antigen-specific T cells. Delayed-type hypersensitivity skin tests (e.g., PPD) reflect antigen-specific memory T-cell activity in vivo. Because all three evaluate T-cell–dependent responses, the most inclusive answer is correct.

Step-by-Step Solution:Map each method to a T-cell function (cytokine release, cytotoxicity, DTH).Recognize that each provides evidence of CMI.Choose “All of the above.”

Verification / Alternative check:Clinical immunology practice routinely uses DTH skin testing; research labs employ CTL assays and migration inhibition as functional readouts.

Why Other Options Are Wrong:

• Each single method is valid but incomplete alone.
• Complement fixation assesses antibodies and complement activation, not CMI.

Common Pitfalls:Equating antibody titers with CMI; humoral immunity is distinct from T-cell–mediated mechanisms.

Final Answer:All of the above.