Final answer:
The molecule that suppresses T-cell activation when interacting with B7 is CTLA-4. Additionally, cytotoxic T lymphocytes (CTLs) bind MHC I molecules on APCs via CD8 coreceptors.
Step-by-step explanation:
The cell surface molecule that, when interacting with B7, suppresses T-cell activation is CTLA-4. CTLA-4 is a protein receptor that acts as an immune checkpoint and downregulates immune responses. It competes with CD28 for binding to B7 on antigen-presenting cells (APCs). While CD28 binding to B7 promotes T-cell activation, CTLA-4 binding to B7 inhibits activation, helping to maintain immune homeostasis and self-tolerance. Therefore, the correct answer is C. CTLA-4.
In the context of question 9, which asks which immune cells bind MHC molecules on APCs via CD8 coreceptors on their cell surfaces, the answer is cytotoxic T lymphocytes (CTLs). These cells are also known as CD8+ T cells. Upon recognizing antigen-MHC I complexes on APCs, CTLs become activated and can directly kill infected cells.