Final answer:
The expression of MHC class II molecules is increased by the secretion of compounds such as cytokines.
Step-by-step explanation:
The expression of MHC class II molecules is increased by the secretion of compounds such as cytokines. Cytokines are small proteins that are released by cells of the immune system in response to an infection or inflammation. They play a crucial role in regulating the immune response, including the upregulation of MHC class II expression.
For example, interleukin-1 (IL-1) and interferon-gamma (IFN-γ) are two cytokines that have been shown to upregulate MHC class II expression. IL-1 is produced by macrophages and dendritic cells, while IFN-γ is mainly produced by T cells. When these cytokines bind to their respective receptors on antigen-presenting cells, they signal the cells to increase the production and surface expression of MHC class II molecules.
In summary, the secretion of cytokines, such as IL-1 and IFN-γ, can increase the expression of MHC class II molecules on antigen-presenting cells.