what is immunity
protection from infectious diseases
how does the immune system achieve this
limiting invasion of foreign agents and destroys damaged and infected cells
what mechanism is the immune system
it is a defence mechanism against harmful invading micro - organisms such as bacteria, vrisuses and fungi.
what is innate immunity
- non specific defence
- passive, a physical anf chemical barrier to the entry of pathogens
- active, humoral - complements , blood proteins
-cellular, NK cells & phagocytes
what is adaptive immunity
- specific defences
- humoral, antibodies
- celuloar , T cells
Characteristics of innate immunity
- Inborn
- older in evolutionary development
- non specific for diff pathogens
- rapidly deployed
- non - adaptive, do not increase with repeated exposure
- provide initial defnce to stop infection and contain it until adaptove immunity develops
Main immune cells of innate immunity
- macrophages
- neutrophils
- eosinophils
- NK cells
Characteristics of adaptive immunity
- accquired after exposure
- relatively later addition in verterbrates
- highly specific for the pathogen responsible fpr the initial infection
- requires 3/7 days to activate
- highly adaptive, increases with each occuring exposure
- devloped if innate sytem is penetrated and needed for ultimate clearance of the infective agent.
main immune cells of adaptive immunity
- B lympocytes
- T lymphocytes
- macrophages
- antigen presenting cells APCs
What are cytokines
- the chemical mediators (hormones) of the immune sytem.
- are small soluble proteins produced by cells of the innate and adaptive immunity, 100s of cytokines and more being discovered
- immune system
what is the role of cytokines in the immune response
- immune response requires actions of cells and many immunocytes of other systems.
- communications bewteen cells involve both specialized physical contacts between them snd release chemical mediators such as cytokines.
antibodies
produced by activated B-lymphocytes.
Structure of antibodies
- has a Y shaped structure with two identical heavy chains and two identical light chains.
- each chain contains both constant segment and variable segment.
function of antibodies.
- an antibody molecule has two antigen binding sites which form from the segments of the chains which bind to antigenic determinant sites/ etiopes of antigen molecules.
- differences in the structure of the variable segments affect the shape and binding site.
- the differences make the antibodies specific for different antigens.
facts
Each b cell is commited to produce antibody of one specificity.
The class that the antibody will produce depends on the way the B cell is activated by the antigen in the lymphoid tissue which is determined by the nature of the antigen.
Consequences of antigen - antibody interactions
- neutralization and agglutination
- opsonisaation, increasing phagocyte effeciency
- complement fixation
- prevention of bacterial viral adhesion
- stimulation of inflammation
what is neutralization and agglutination ?
- is caused by the change in the physical property due to the formation of the complex.
what are T cells
T cells are responsible for cell - mediated adaptive immunity
types of T cells
- when antigen triggers the adaptive immune response T cells are activated first before B cells.
- T cells (CD8 T cells) directly attacl infected& altered cells such as tumour cells.
- CD4 T cells/ helper cells are often the only and first activated T cells responding to intracellular bacteria in immune reponses.
- Helper T cells stimulate B cells so correct antibdoies are made and help CD8 t cells to beecome activated.
what are CD4 and CD8
- they are self surface molecules which are present on the cells which help them to characterise them.
- CD4 T helper cells are the first immunocytes to get activated by the antigen.
- they cannot percieve the antigenm on their own and has to be presented by anotehr cell in the correct way.
what are APC’s
- the cells that present antigem to the T cells so they become activated are known as Antigen - Presenting cells
Types pf APC’s
- dendritic cells
- activated macrophages
- B cells
the cells internalise the antigen, breakes them into smaller fragments.
Antigen recognition by T cells
- for T cells to be activated the processed antigens need to be presented by antigen presenting cells such as peptide antigens.
- CD4 T helper cells recognise antigens of extracellular origin wheras antigens of cytoplasmic origin are recognised by CD8 T cells.
what is the second signal
Co - stimulation which acts as a confirmation of initial signal for T cells to become activated.
