Immune disorders Flashcards
Define the immune system?
A collection of mechanisms that protect against disease by identifying and killing pathogens, and tumour cells, and protection against microbial toxins.
What are the two major components of the immune system?
- Innate immunity
- Adaptive immunity (acquired)
Describe the innate immunity
Does not require prior exposure to a microbe to mount an immune response - it is always present and ready to attack.
-Born with, not specific
-Exposure leads to immediate maximal response
-Found in nearly all forms of life
-Phagocytes, NK cells, complement system
Describe the adaptive immunity
A more advanced system requiring exposure to an antigen in order to become active against microbes which have evaded the innate system
-Stronger immune response
-Specific and requires previous exposure to a stimulant
-Lag time between exposure and maximal response
-Cell mediated and humoral (antibody components)
-Exposure leads to immunological memory
-Found only in jawed vertebrates
-Highly malleable system due to somatic hypermutation and VDJ recombination of antigen receptor genes. Allows a small number of genes to generate an enormous number of antigen receptors that are uniquely expressed on each individual lymphocyte.
-Major components: lymphocytes (B cells and T cells), antigen presenting cells (dendritic cells, macrophages), human major histocompatibility complex (MHC) and complement system
Define immunology
The science that examines the structure and function of the immune system
Describe pathogens
Viruses, bacteria, mycobacteria, parasites and fungi
What are the general characteristics of immunity? (5)
- Recognition: the ability to distinguish between normal self, altered (damaged) self and non-self (foreign material)
- Specificity: the ability to inactivate, destroy and remove the “offending” material, without damaging normal tissues in the vicinity of the reaction, i.e. the reaction must be target-specific
- Regulation: the immune system is able to control the type, intensity and duration of the reaction and has the ability to prevent immune reaction (suppression)
- Amplification: the effector (attack) phase of the immune reaction is mediated through multiple pathways which act synergistically for optimal effect.
- Memory: the identity of the foreign material (antigen) which led to the first (primary) immune response is remembered so that the next episode involving the same antigen will result in an accelerated reaction (secondary immune response), which by-pass several initial steps that the primary immune response has to go through (confers long-term immunity).
What are natural killer cells?
-Recognized and destroy virus-infected cells as well as other damaged cells and tumour cells
-Recognize self via MHC class I molecules (expressed on all healthy cells)
-Damaged cells/tumour cells may not express normal MHC I, and NK cells will destroy them
-Damaged or stressed cells may bind to activating receptors on NK cells
-Express inhibitory and activating receptors. The receptor for MHC class I is an inhibitory receptor.
-They have innate ability to lyse viral infected cells and tumour cells without previous sensitization
-Produce the cytokine interferon in order to activate - interferon promotes their killing activity
-10-15% of peripheral cells; do not bear T-cell receptors or cell surface immunoglobulins
- Ability to lyse IgG-coated target cells (antibody-dependent cell-mediated cytotoxicity, ADCC)
- Have Cd16 and Cd56 surface molecules
- Prostaglanding E2 is highly suppressive of NK cells
What are the components of the innate immunity?
- Surface barriers - mechanical (skin), chemical (enzymes in saliva, vaginal secretions, tears), biological (bacterial flora)
- Humoral and chemical barriers - inflammation (one of first responses, produced as a result of: cytokines (e.g. interleukins), prostaglandins, leukotrienes, chemokines and interferons)
What are the cellular components of inflammation?
- Neutrophils: phagocyte and release enzymes
- Eosinophils and basophils: secrete chemical mediators
- Monocytes/ macrophages: attack pathogens by engulfing and then killing the microorganisms by enzymes present within “lysosomes”
- Mast cells: regulate the inflammatory response
-Dendritic cells: phagocyte - Natural killer cells
Describe the complement system
It consists of more than 20 proteins and named as such due to its ability to “complement” the killing of a pathogen. They are synthesized mainly in the liver and normally circulate in the blood (plasma) in an inactive form.
-Recognize components of microbes (endotoxin, mannose residues) and are activated.
What can complement proteins be activated by?
- Proteases (damaged cells, bacterial endotoxins) - proteolysis activates
- Binding of the complement to antibodies that are attached to microbes
- Binding complements carbohydrates on the microbes’ surfaces
What does complement activation result in?
-May form complexes with other complement proteins to kill microbes by direct cell lysis (membrane attack complex)
-Cell membrane disruption (lysis of target cell)
-Opsonization (coat) an organism, marking it for destruction
-Attraction of other immune cells through the production of peptides
-Release of various factors e.g. anaphylatoxins and chemotactic factors which result in acute inflammation
-Can also trigger the coagulation system, kinin system and fibrinolytic system
*May act as inflammatory mediators to recruit leukocytes, or may act as opsonins (C3b), coating microbes to target them for phagocytosis.
What are the two main types of adaptive immunity?
- Humoral immunity
- Cell mediated immunity
Describe humoral immunity
- Antibody (immunoglobulin) - mediate, targets extracellular microbes
- Antibodies are produced by plasma cells and are specifically directed against a particular antigen
- Antibodies can neutralize microbes, promote their phagocytosis and destruction, and activate the complement system
