Review Question - QID 109422

The researcher is studying a cell that expresses CD8, a cell surface marker that interacts with class I major histocompatibility complex (MHC) molecules. Cytotoxic T lymphocytes express CD8 and require co-activation via IL-2 from activated helper T-cells.

The activation of cytotoxic CD8+ T-cells is a multi-step process. First, T-cells form loose attachments with host cells that are presenting foreign antigens on class I MHC molecules. This process is mediated by interactions between LFA-1 and ICAM-1. Next, the T-cell receptor recognizes and binds antigen while the CD8 co-receptor binds the constant portion of the class I MHC molecules. Third, co-activation via IL-2 from helper T cells is required to fully activate the cytotoxic T cell. Alternatively, co-activation may occur via interactions between CD28 on the T-cells and CD80/86 on the host cell.

Incorrect Answers:
Answer 1: Interleukin 1 (IL-1) is a pro-inflammatory molecule that stimulates the growth of B cells, neutrophils, fibroblasts, and epithelial cells. IL-1 also induces T lymphocytes to express IL-2 receptors. Therefore, it only plays an indirect role in cytotoxic T lymphocyte activation.

Answer 3: Interleukin 4 (IL-4) functions to induce class switching from IgM to IgG and IgE. It does not play a role in cytotoxic T lymphocyte activation.

Answer 4: Interleukin 6 (IL-6) is a pro-inflammatory molecule that increases the production of acute phase reactants such as fibrinogen, C-reactive protein, and hepcidin. It does not play a role in cytotoxic T lymphocyte activation.

Answer 5: Interleukin 8 (IL-8) is a pro-inflammatory molecule that serves as a chemotactic agent to attract neutrophils. It does not play a role in cytotoxic T lymphocyte activation.

Bullet Summary:
The activation of cytotoxic T-cells involves interactions between CD8 and MHC class I as well as co-activation via IL-2 from activated helper T-cells.