Antibodies are protein molecules that attach themselves to invading pathogens, such as bacteria and viruses, marking those pathogens for destruction by other components of the immune system. The immune system is complex, and proper function requires that the cells making up the system interact in a way that ensures that pathogenic cells are attacked, and the body's own cells never are--at least, they shouldn’t be. As such, no single cell type can launch a complete immune response on its own--checks and balances within the immune system require many different cells to be in agreement regarding the pathogenic nature of an invader for an attack to occur.
The cells most ostensibly involved in antibody production are the B cells, so named because they mature in a structure called the “bursa” of a chicken, the animal in which they were discovered. Humans, lacking a bursa, nevertheless produce B cells--in humans, they mature in the bone marrow, Dr. Gary Thibodeau explains in his textbook, “Anatomy and Physiology.” These cells make antibodies if stimulated to do so, but they are incapable of stimulating themselves. In other words, if a B cell capable of producing chickenpox antibodies encountered a chickenpox virus in the bloodstream, it would not react to that virus at all. Instead, B cells respond only to signals from other immune cells, informing them that an invader is pathogenic.
One of the simplest pathways to B cell activation involves antigen-presenting cells, or APCs. These cells consume suspicious particles in the body, chemically digest them and then present their structural components on the outside of the APC. This “showcase” of a potential pathogen’s working parts helps other immune cells identify invaders quickly. APCs consume particles without regard to whether they’re actually pathogenic, explains Dr. Thibodeau. If a particle is not pathogenic, no other immune cells will respond to the APC’s “showcase” of parts. If the particle is pathogenic, however, other immune cells quickly notice.
Helper T Cells
Helper T cells, named for the fact that they mature in a structure called the thymus, are among the immune cells that notice if an APC is showcasing pathogenic parts, Dr. Lauralee Sherwood explains in her book, “Human Physiology.” The helper T becomes activated on contact with an APC that is displaying an invader, and the helper T goes on to find B cells that are capable of producing antibodies to that pathogen. For instance, if the APC stumbled upon a chickenpox virus, a helper T would notice and would find B cells capable of making chickenpox antibodies. The helper T would activate those B cells, and they would begin making antibodies. The antibody would circulate through the bloodstream, sticking to other chickenpox viruses and marking them for destruction. While the process takes time, eventually the immune system is capable of eradicating infection in this way.