What are those Y-shaped things floating around the cell?
Humoral Immune Response
There are actually two types of immune responses: humoral and cell-mediated. The humoral immune response involves mainly B cells and takes place in blood and lymph.
B Cell Activation
B cells must be activated by an antigen before they can fight pathogens. This happens in the sequence of events shown in Figure below. First, a B cell encounters its matching antigen and engulfs it. The B cell then displays fragments of the antigen on its surface. This attracts a helper T cell. The helper T cell binds to the B cell at the antigen site and releases cytokines that “tell” or signal the B cell to develop into a plasma cell.
Activation of a B cell must occur before it can respond to pathogens. What role do T cells play in the activation process?
Plasma Cells and Antibody Production
Plasma cells are activated B cells that secrete antibodies. Antibodies are large, Y-shaped proteins that recognize and bind to antigens. Plasma cells are like antibody factories, producing many copies of a single type of antibody. The antibodies travel throughout the body in blood and lymph. Each antibody binds to just one kind of antigen. When it does, it forms an antigen-antibody complex (see Figure below). The complex flags the antigen-bearing cell for destruction by phagocytosis.
An antibody matches only one type of antigen.
Most plasma cells live for just a few days, but some of them live much longer. They may even survive for the lifetime of the individual. Long-living plasma cells are called memory cells. They retain a “memory” of a specific pathogen long after an infection is over. They help launch a rapid response against the pathogen if it invades the body again in the future.
- Activated B cells produce antibodies to a particular antigen.
- Memory B cells remain in the body after the immune response is over and provide immunity to pathogens bearing the antigen.
- How do plasma cells help fight pathogens? Include the role of antibodies in your response.
- If a disease destroyed a person’s helper T cells, how might this affect the ability to launch an immune response?
- What are memory cells? What is their role?