The immune system makes antibodies when a bacteria, pollen or a virus invades the body. When a person is exposed to the same foreign materials, the immune system usually recognizes the foreign materials thus releasing the specific antibodies that react with the foreign material and destroys it.
It can be noted that the immune system releases antibodies that have the same shape with the foreign materials or antigen for the purpose of eliminating the antigen.
The antibodies are made by lymphocytes. This originates from the bone marrow which later circulates in the bloodstream. In this case, they patrol the body through the blood circulation. Swelling of the lymph nodes indicates that they are filled with the cells that attack the foreign materials.