Multiple Choice
Cytotoxic T cells are responsible for which of the following responses?
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21. The Immune System
T Cells
Multiple Choice
In a typical adaptive immune response, naïve T-cell activation requires which of the following?
A
Recognition of free (soluble) antigen by the T-cell receptor without MHC presentation
B
Binding of IgG Fc regions to the T-cell receptor as the primary activation signal
C
Recognition of peptide antigen on MHC by the T-cell receptor plus a costimulatory signal (e.g., CD28 binding B7)
D
Antigen binding to MHC class I on the T cell itself without costimulation
Verified step by step guidance1
Step 1: Understand the role of the T-cell receptor (TCR) in antigen recognition. Naïve T-cells recognize antigens only when they are presented as peptide fragments bound to Major Histocompatibility Complex (MHC) molecules on the surface of antigen-presenting cells (APCs). Free or soluble antigens are not recognized directly by the TCR.
Step 2: Recognize that T-cell activation requires two signals. The first signal is the specific recognition of the peptide-MHC complex by the TCR. The second signal is a costimulatory signal, which is necessary to fully activate the T-cell and prevent anergy (a state of non-responsiveness).
Step 3: Identify common costimulatory molecules involved in T-cell activation. For example, CD28 on the T-cell binds to B7 molecules (CD80/CD86) on the APC, providing the essential second signal.
Step 4: Eliminate incorrect options based on these principles: T-cells do not recognize free antigen without MHC, they do not get activated by binding IgG Fc regions, and antigen binding to MHC class I on the T cell itself without costimulation is insufficient for activation.
Step 5: Conclude that the correct activation mechanism involves recognition of peptide antigen presented on MHC molecules by the TCR along with a costimulatory signal such as CD28 binding to B7.
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