The immune system is a complex network of different organs, cells, and proteins that work together. There are 2 main parts of the immune system: the innate immune system - you are born with this, and the adaptive immune system - you develop this when your body is exposed to microbes or chemicals released by microbes. These two immune systems work together. The Innate Immune System This is your child’s rapid response system. It is the first to respond when it finds an invader. It is made up of the skin, the eye's cornea, and the mucous membrane that lines the respiratory, gastrointestinal, and genitourinary tracts. These all create physical barriers to help protect your child's body. They protect against harmful germs, parasites (such as worms), or cells (such as cancer). The innate immune system is inherited. It is active from the moment your child is born. When this system recognizes an invader, it goes into action right away. The cells of this immune system surround and cover the invader. The invader is killed inside the immune system cells (called phagocytes). The Acquired Immune System The acquired immune system, with help from the innate system, makes special proteins (called antibodies) to protect your body from a specific invader. These antibodies are developed by cells called B lymphocytes after the body has been exposed to the invader. The antibodies stay in your child's body. It can take several days for antibodies to form. But after the first exposure, the immune system will recognize the invader and defend against it. The acquired immune system changes during your child's life. Immunizations train your child’s immune system to make antibodies to protect them harmful diseases.