Which of the following statements is true about MHC-II?

MHC II molecules play a crucial role in the immune system, specifically in the activation of T-helper cells, also known as CD4+ T cells. These molecules are primarily expressed on antigen-presenting cells such as dendritic cells, macrophages, and B cells. The interaction between MHC II and T-helper cells is essential for the adaptive immune response, as T-helper cells recognize processed antigens presented by MHC II. This recognition leads to the activation and proliferation of T-helper cells, which subsequently assist in orchestrating a broader immune response, including the activation of B cells and cytotoxic T cells.

Other options do not correctly describe MHC II. For instance, it is not found on all body cells, as only a subset of immune cells express these molecules. MHC II specifically interacts with T-helper cells rather than CD8+ T cells, which are recognized by MHC I molecules. While MHC II is involved in antigen presentation and signaling, the primary and most well-known function is its interaction with T-helper cells, facilitating the adaptive immune response.