And the decline phase takes place because our body is actually winning. Our antibodies are binding to the antigens and they are labeling them for destruction. And so our immune system is able to destroy the infecting pathogens along with their antigens. And so that's why eventually, over time we see a drop in our concentration of immunoglobulbulins until it drops to very low undetectable levels as shown in the following diagram. And so this process ultimately takes place about four weeks as shown in this particular case for this particular invading pathogen. Now, the primary immunoglobulin that is used for this particular primary response and in general, the major type of antibody that is used for all primary responses is immunoglobulin M. So remember, we have five different classes of antibodies.