Middle School Life Science: Diseases and the Body's Defenses - Immune System Defense — Flashcards

The human body has three primary lines of defense to fight against foreign invaders, including viruses, bacteria, and fungi. The immune system’s three lines of defense include physical and chemical barriers, non-specific innate responses, and specific adaptive responses.
There are two different types of lymphocytes, called B cells and T cells. The two types of cells launch an immune response, but they do so in different ways.    
B cells respond to pathogens in the blood and lymph. Most B cells fight infections by making antibodies. An antibody is a large, Y-shaped molecule that binds to an antigen. Each antibody can bind with just one specific type of antigen. The antibody and antigen fit together like a lock and key. Once an antibody binds with an antigen, it signals a phagocyte to engulf and destroy them, along with the pathogen that carries the antigen on its surface.    
There are different types of T cells, including killer T cells and helper T cells. Killer T cells destroy infected, damaged, or cancerous body cells. When a killer T cell comes into contact with such a cell, it releases toxins. The toxins make tiny holes in the cell's membrane. This causes the cell to burst open. Both the cell and any pathogens inside it are destroyed.    
Helper T cells do not destroy infected, damaged, or cancerous body cells. However, they are still needed for an immune response. They help by releasing chemicals that control other lymphocytes. The chemicals released by helper T cells “switch on” B cells and killer T cells so they can recognize and fight specific pathogens.