Which interaction provides the essential second signal for T cell activation after antigen recognition?

Which interaction provides the essential second signal for T cell activation after antigen recognition?

• A. TCR-MHC recognition
• B. CD28-B7 interaction
• C. Complement activation
• D. Antibody cross-linking of B cell receptors

Answer: (B)

T cell activation requires two signals. The first comes from the T cell receptor recognizing a peptide presented by MHC on an antigen-presenting cell. The essential second signal is provided by CD28 on the T cell binding to B7 (CD80/CD86) on the APC. This costimulatory interaction drives IL-2 production and T cell proliferation, and without it the T cell may become anergic or undergo apoptosis even if the antigen is recognized. Complement activation and antibody cross-linking of B cell receptors involve other parts of the immune system and do not provide the necessary T cell costimulation. Therefore, the CD28-B7 interaction is the key second signal for T cell activation.

T cell activation requires two signals. The first comes from the T cell receptor recognizing a peptide presented by MHC on an antigen-presenting cell. The essential second signal is provided by CD28 on the T cell binding to B7 (CD80/CD86) on the APC. This costimulatory interaction drives IL-2 production and T cell proliferation, and without it the T cell may become anergic or undergo apoptosis even if the antigen is recognized. Complement activation and antibody cross-linking of B cell receptors involve other parts of the immune system and do not provide the necessary T cell costimulation. Therefore, the CD28-B7 interaction is the key second signal for T cell activation.