Fish Immunology (1+1)

Unit 5- Specific defence mechanism in Fish

5.1.5. Cell-Mediated Immunity (T cells)
Antigenic fragments present on the macrophage alert a specific type of T lymphocyte (“helper” T) about the attack of intruder. These helper T cells recognizes antigen particles and binds to the macrophage via an antigen receptor. Helper T cells are unique to a specific antigen.

This binding stimulates production of chemical substances such as interleukin-1 (IL-1), tumor necrosis factor (TNF) by macrophage
Helper T cells generates interleukin-2 and gamma interferon (IFN-y)
All substances facilitate intercellular communication

TNF steps up production of IL-1, it also causes fever in homeotherms
TNF and IL-1 are cytokines (cellular)
Apart from causing fever IL-1 forms immune cell clusters and stimulates the helper T cell to release IL-2
IL-2 causes T cells to release gamma interferon which, in-turn, activates macrophages
IL-2 also instructs other helper T cells and “killer” T cells to multiply
Proliferating helper T cells release substances that cause B cells (another type of lymphocyte) to multiply and produce antibodies

Meanwhile, many invader cells have been consumed by macrophages, but other “daughter” viral particles have escaped and are infecting other cells
Killer T cells will kill the host cells that are infected with virus by making pores to the infected cell.

Finally, as the infection is brought under control, yet another type of T cell called the suppressor T cell will signal B cells, helper T’s and killer T’s to stop the work.
After the work has stopped most immune cells die, but a few remain in the body these are called memory cells. This memory cells will keep the memory of the antigen so that they will be able to respond more quickly the next time the body is invaded by the same foreign substance