Now, what about the constant regions? So basically earlier we said that we have five different types of five different classes or five different types of antibodies. Now, each class of antibody has the same exact constant region. But these constant regions do change when we go from one type to a different type. In fact, these constant regions determine the type of class that we're dealing with and they actually determine the mechanism that our antibody uses to basically fight off infections and fight off these pathogenic invasions. And on top of that, it's these constant regions, the bottom portion of these constant regions that actually bind onto the cell membranes of immune cells and other cells of our body.