Teddies Talks Biology - Issue 9

(continued)

Another component of this immune response are sentinel cells, which can be found in skin or mucosal surfaces. They travel through the body, looking for signs of infection. They are either dendritic cell or macrophages. Dendritic cells bind cytokines produced by virus - infected cells and respond by producing even more cytokines to amplify the immune response. In the case of many viral infections, this early reaction is enough to eliminate pathogens. If innate defenses are overwhelmed, the second - line defense is mobilized to ensure host survival.

The adaptive immune system is com- posed of specialized cells and process- es, and it relies on the clonal expansion of plasma cells to produce sufficient numbers of antibodies. This results in a delay between initial pathogen expo- sure and the production of antibodies. If the pathogens are able to reproduce rapidly in the meantime, they can dis- rupt normal body functioning and cause disease. As a result of previous expo- sure, memory cells are produced. They are produced to prevent this delay in subsequent exposures and the devel- opment of symptoms. The adaptive im- mune response begins when an imma- ture dendritic cell ingests a pathogen in

the infected tissue. It becomes activated and travels to a lymph node. The dendritic cell then matures into an antigen - presenting cell and undergoes changes that allow it to activate patho- gen - specific lymphocytes that are in the lymph nodes. Pathogen antigens are carried to the T lymphocytes. T lymphocytes stimulate B lymphocytes. A small proportion of the B lymphocytes differentiate into memory cells. They survive for many years, providing low levels of circulating antibodies. In case of a second infection with the same pathogen, the memory cells will react quickly and produce antibodies. With antibodies being produced fast, the pathogen is not able to reproduce in sufficient amounts to cause symptoms. This means that exposure to that path- ogen does not cause disease to occur, and the individual is immune.

Teddies Talks Biology I Issue 9 I June 2021

9