The third line of defence
The third line of defence focuses on the target of specific antigens that have entered the body. It is adaptive, which means it is able to adapt or 'learn'.
Lymphocytes are the cells that are responsible for the third line of defence. They include:
Lymphocytes are the cells that are responsible for the third line of defence. They include:
Cell-mediated response (T cells):
This type of response starts off with an antigen invading the body. Macrophages then engulf it via phagocytosis, and it is then presented to the lymphocytes. The body knows which cells to engulf as the ones that belong to the immune system are identified as 'self' by marker proteins on the surface of the plasma membrane. These marker proteins are called the major histocompatibility complex (MHC). MHC markers are unique to every individual (apart from identical twins). Antigens are not displaying MHC markers that belong to that individual, which means they are identified as 'non self' and destroyed. T cells do not bind with antigens directly but with the antigens presented on the MHC markers.
The different types of T cells and their function in cell-mediated response can be seen in the table above.
Humoral immunity (B cells):
B-cells make Y-shaped proteins called antibodies in response to an antigen. Antibodies bind to specific antigens that induce their production. Antibodies that are directed against antigens on the surface of foreign pathogens allow them to be eliminated from the body. It allows elimination as the antibodies act as markers; the phagocytes can identify them as foreign material easier.
If a B cell comes into contact with a complementary shaped antigen, it will form a clone of itself (similar to that of T cells). The clone contains plasma cells for immediate use and a smaller amount of memory cells which will be used in the future.
B cells cannot leave the lymph nodes (unlike T cells) so only the antibody that they create can move around the body. The antibody is released into the bloodstream and essentially carried to the area of infection.
The different types of B cells and their function in humoral immunity responses can be seen in the table above.
This type of response starts off with an antigen invading the body. Macrophages then engulf it via phagocytosis, and it is then presented to the lymphocytes. The body knows which cells to engulf as the ones that belong to the immune system are identified as 'self' by marker proteins on the surface of the plasma membrane. These marker proteins are called the major histocompatibility complex (MHC). MHC markers are unique to every individual (apart from identical twins). Antigens are not displaying MHC markers that belong to that individual, which means they are identified as 'non self' and destroyed. T cells do not bind with antigens directly but with the antigens presented on the MHC markers.
The different types of T cells and their function in cell-mediated response can be seen in the table above.
Humoral immunity (B cells):
B-cells make Y-shaped proteins called antibodies in response to an antigen. Antibodies bind to specific antigens that induce their production. Antibodies that are directed against antigens on the surface of foreign pathogens allow them to be eliminated from the body. It allows elimination as the antibodies act as markers; the phagocytes can identify them as foreign material easier.
If a B cell comes into contact with a complementary shaped antigen, it will form a clone of itself (similar to that of T cells). The clone contains plasma cells for immediate use and a smaller amount of memory cells which will be used in the future.
B cells cannot leave the lymph nodes (unlike T cells) so only the antibody that they create can move around the body. The antibody is released into the bloodstream and essentially carried to the area of infection.
The different types of B cells and their function in humoral immunity responses can be seen in the table above.