When an antigen or foreign substance invades the body, the immune system gets activated and works to identify and eliminate the invading substance. 

B lymphocytes, which are cells of the immune system, are triggered to produce proteins known as immunoglobulins or antibodies. The antibodies recognize and bind to specific antigens, changing their conformation. T cells, which are another type of immune system cells, destroy the antigens that are tagged by antibodies. 

Humans have three types of immunity that work together to protect the body against disease:

• Innate immunity is a type of general protection that everyone is born with.
• Adaptive immunity is a continuously developing type of immunity that we develop on exposure to diseases or by immunization through vaccines. 
• Passive immunity is a type of short-term immunity that’s temporarily borrowed from another source such as a baby getting temporary immunity through antibodies in a mother’s breast milk.