Final answer:
Peptides that bind to MHC class II molecules typically range from 13 to 25 amino acids in length, are presented by APCs, and interact with CD4 molecules on T cells.
Step-by-step explanation:
The length of the peptides that bind to MHC class II molecules typically ranges from 13 to 25 amino acids. These peptides are presented on the surface of antigen-presenting cells (APCs) such as macrophages, dendritic cells, and B cells. The MHC class II molecules are made up of two subunits of approximately equal size, an α and a β chain, which both span the plasma membrane. The antigen-binding cleft, where peptides bind, is formed by the α₁ and β₁ domains of MHC class II molecules. This cleft accommodates peptides that can interact with CD4 molecules on T cells, an essential process for the effective activation of the immune response.