Fish Immunology (1+1)

Unit 1- Fish Immunology

1.3. Adaptive immunity
Adaptive immunity also called specific or acquired immunity develops more slowly and take part after innate immunity, adaptive immunity is even more effective against pathogens. Adaptive immunity is stimulated by the presence of pathogens.
If the pathogen survives the innate immunity, adaptive immunity develops later and mediated by lymphocytes and their products. Where antibodies block infections and eliminate pathogens, T lymphocytes also helps in eradicating intracellular microbes.
There are two types of adaptive immunity

• Humoral immunity and
• Cell-mediated immunity

Humoral immunity
Humoral immunity is mediated by the antibodies which are immunoglobulins and these immunoglobulins are produced by plasma cells differentiated from B cells.
Antibodies are formed against antigens, secreted into the blood and mucosal fluids so these antibodies can neutralize and eliminate pathogens and microbial toxins that are harmful to host.
Cell-mediated immunity
Cell-mediated immunity is mediated by different immune cells that are formed to provide protection against pathogen.
Antibodies cannot reach the pathogen that divide inside infected cells. Defense against such intracellular pathogens is mediated by cell mediated immunity. Cell mediated immunity is mainly through T lymphocytes. Here a type of T lymphocyte, stimulates the phagocytes to quickly recognize the pathogen and destroy them. Other T lymphocytes kill any type of host cells that are harboring infectious microbes in their cytoplasm.
Adaptive immunity may be sub-divided into two major types depending on how the immunity was introduced.
Naturally acquired immunity occurs through contact with a pathogen in environment, whereas artificially acquired immunity develops with vaccination.
Both naturally and artificially acquired immunity can be further subdivided depending on whether immunity is induced in the host or passively transferred from an immune host. Passive immunity is acquired through transfer of antibodies or activated T-cells from an actively immunized host, passive immunity may last only a few months, whereas active immunity is induced in the host by vaccination, and lasts longer duration may be life-long.
An individual exposed to an antigen of a microbe develops an active immune response to eradicate the infection and develops resistance to later infection by that microbe. Such and individual is said to be immune to that microbe.
The most important properties of adaptive immunity is the fine specificity for antigens and memory to the prior exposed antigen.
The tissue of the immune system consist of primary lymphoid organs, in which T and B lymphocytes mature and become competent to respond to antigens, and the peripheral or secondary lymphoid organs, in which adaptive immune response to microbes are initiated.