Immunology Flashcards
What physical barriers does the body have to keep out infecting organisms?
Skin
Mucociliary escalator (upward flow of mucus in bronchi)
Complete emptying of bladder
What simple chemical and biological barriers help the body prevent invasion from infecting organisms?
Low pH in stomach and vagina
Sebum on skin
Normal flora on skin, in bowel and in vagina
What cells and molecules form immunological defence mechanisms?
Lymphocytes, macrophages, antibodies and complement
Why is it important for immunological agents to have recognition capabilities?
To distinguish from self and non-self and tell the difference between damaged and healthy tissues.
Prevent autoimmunity
Define ‘immune response’.
Activation of the destructive agents that form the body’s immunological defence mechanisms (lymphocytes, macrophages, antibodies and complement)
Define ‘immunogen’.
Anything that provokes an immune response
Define ‘antigen’
Anything that is recognised by the cells and molecules of the immune response
Define ‘determinant’
Agents of the defense system recognise antigens through receptors and recognition sites. The part of the antigen that is recognised is called a determinant.
Define ‘receptor’
A molecule or complex of molecules which has at least one recognition site (for recognising a determinant on an antigen). Normally present on the surface of cells.
Why is recognition important in relation to immune response?
The immune system needs:
- to detect the presence of non-self and, usually, to destroy and/or eliminate the invader
- to leave I damaged, as much as possible; the body’s own components (self)
- sometimes to allow toleration of some non-self substances where an aggressive immune response serves no useful purpose
How does a receptor bind to the determinant?
Complementary shapes and electrostatic forces
How do antigen receptors aid immunity?
Antigen receptors recognise determinants that are present on non-self substances, but are sparse or absent on self - thus distinguishing self and non-self.
How do scavenger receptors aid immunity?
Scavenger receptors recognise determinants or features characteristic of dead or denatured material, but scarce or absent on healthy issue - thus distinguishing damaged and healthy tissue
Receptors and determinants are used to identify targets of the immune system. How else are they used?
Cells and molecules of the immune system also interact and cooperate with each other through specialised receptors and determinants, such as:
- receptors on macrophages for antibodies
- interactions within the complement cascade
If a receptor binds only to one particular kind of determinant it is said to be __?__.
very specific
A receptor may bind to a variety of determinants with a common property (e.g. May bind to all determinants with a strong negative charge, because it has a strong positive charge) in spite of there being differences in their shapes. A receptor of this type is said to be __?__.
Non-specific
What are antigens usually made of?
Antigens are usually polypeptides or polysaccharides, sometimes with other chemical groups attached
True or false: each antigen has one determinant
False, antigens may have several determinants recognisable by the receptors of the defence system.
How can cells that are part of the immune response communicate with each other?
Cell surface molecules: cells touching each other may communicate through structures that allow them to fit or bind together to mediate communication.
Secreted molecules, or mediators: such as hormones, cytokines, or lymphokines
How do lysosomes assist in the body’s defence?
Lysosomes act by damaging bacterial cell walls, but do no harm to eukaryotes, which lack a cell wall
How does mannose-binding protein assist in the body’s defence?
Mannose-binding protein acts through recognition of particular carbohydrate patterns found on the surface of many pathogenic microorganisms.
How does C-reactive protein (CRP) assist in the body’s defence?
CRP binds to phosphorylcholine on bacteria, enhancing phagocytosis and assisting in complement binding.
What is the complement pathway?
A cascade system of enzymes reminiscent of the clotting pathway and is triggered by certain foreign chemical configurations found in endotoxins, and bacterial and fungal cell walls. It culminates in the activation of enzymes destructive to foreign organisms. It also produces chemotactic substances and adherent factors that promote the phagocytosis. It also acts to discriminate self and non-self as it is only stimulated by foreign material.
How do chemotactic factors assist in the body’s defence?
Chemotactic factors are chemical substances that direct the movement of cells – human or invading – to particular locations.
“All body cells play their part in the innate immune system.”
In what ways do they do this?
Any cell that is damaged or undergoes necrosis may release mediators, or material such as heat shock proteins that signal the damage to neighbouring cells.
Many cells that are virally infected signal the fact by releasing mediators (interferons (IFNs)).
Phagocytes, such as neutrophils, monocytes/macrophages, dendritic cells and eosinophils, play a significant role in the innate immune system, as they can usually kill the microbes they phagocytose.
What methods are used by phagocytes to kill microbes?
Phagocytic destruction mechanisms involve enzymes, free radicals and exclusion of nutrients from the phagosome.
Which defence mechanism uses a relatively small number of receptors and recognition sites that detect components common on microorganisms, but not found within the human body?
a) Innate immune system
b) Adaptive immune system
a) Innate immune system
These mechanisms do not recognise all determinants and successful pathogens hide these. The body needs a more sophisticated defence mechanism to deal with these – the adaptive immune system.
Which defence mechanism employs the use of lymphocytes?
The adaptive immune system
What are the different types of lymphocyte?
- B lymphocytes
- T lymphocytes
- null lymphocytes
There are 3 classifications of lymphocyte: B, T, and null.
T lymphocytes can be further divided into what categories?
- CD4-positive (helper T cells)
- CD8-positive (cytotoxic T cells)
Are lymphocyte receptors specific or non-specific?
Specific.
Any one lymphocyte, and its clone from division of a single cell, will have receptors which are specific for an antigen, but different lymphocytes will have different specificities.
From where do T lymphocytes originate?
T lymphocytes originate in the bone marrow, but undergo further development in the thymus before they are mature.
True or false: Like B lymphocytes, the receptors on the surface of any one T lymphocyte all have the same specificity.
True
The receptors on T lymphocytes are known as __1__. Highly variable, these regions interact with an __2__ to activate the lymphocytes.
1) complementarity determining regions (CDRs)
2) MHC (major histocompatibility complex)-peptide complex
What is CD nomenclature?
CD stands for cluster of differentiation. This is a classification system for the different antigenic determinants found on cells.
The surface molecules are different on different cells and so act as markers of differentiation. The different CD complexes are given a number to differentiate them.
What is the ‘major histocompatibility complex’?
The MHC region is located on chromosome 6 and consists of about 140 genes, many having immunological functions. Proteins produced from fragmented microorganisms bind to various MHC molecules. The MHC molecule can be divided into three groups: class I, class II and class III.
MHC class I
MHC class I molecules are present on the surface of virtually every cell. They present antigen fragments to T lymphocytes and bind to CD8 receptors on cytotoxic T cells.
MHC class II
MHC class II molecules are found mainly on macrophages and B cells and present antigen to helper T cells, binding to the CD4 receptor.
MHC class III
MHC class III genes encode for other immune components, such as complement, or cytokines such as TNF-α.
Human leucocyte antigen (HLA) classifications
HLA antigens are classified into nine divisions:
- HLA-A, HLA-B and HLA-C all belong to MHC class I.
- HLA-D consists of six genes, all belonging to MHC class II.
Human leucocyte antigen (HLA) structures
The HLA molecules, class I and II, are both two-chain glycoproteins. Class I molecules have a single transmembrane chain whereas class II molecules have two transmembrane chains. Both classes have an antigen-presenting groove where oligopeptides bind
How are T lymphocytes activated?
The interaction of a T cell receptor with an MHC-receptor indicates the presence of a cell with a foreign particle, such as an intracellular microbe.
The binding stimulates the T lymphocytes, which become activated and release various cytokines, depending on what type of lymphocyte has been stimulated.
CD4 T lymphocytes (having CD4 receptors, helper T cells) cannot eliminate or kill antigen, so how does their response aid the body’s defence?
When a helper T lymphocyte encounters an antigen of the correct specificity, correctly presented, it responds by dividing and secreting cytokines. These lymphocytes cannot eliminate or kill antigen but the secreted cytokines initiate events that do.
