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Immunology Basics

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by

Rachel Heap

on 16 May 2014

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Transcript of Immunology Basics

IMMUNOLOGY
Definitions and vocabulary
Components
Immune response
Diseases of the immune system
Vaccination
Definitions and vocabulary
Components of the immune system
The immune response
Diseases of the immune system
Vaccination
Problems with the acquired immune system
SCID (severe combined immunodeficiency) – no B or T cells, life expectancy <1year if untreated
HIV/AIDS – destroys helper T cells (CD4 cells), unable to fight opportunistic infections, susceptible to some cancers
The T cells;
regulate, stimulate, and co-ordinate the rest of the response.
are capable of direct destruction of infected cells
The B cells;
produce antibodies which
directly neutralize toxins
attach to antigens to make them more obvious for the killer cells and destructive plasma proteins
bind to viruses to prevent them replicating
Final destruction of the pathogen can happen by a number of different routes, but ultimately it is engulfed by a phagocytic cell and destroyed
If the barriers of the innate (natural) response are breached, pathogens can enter the blood stream or lymphatic fluid
In some cases, antigen presenting cells such as the dendritic cells may recognise the pathogen as ‘foreign’, which is then engulfed
Alternatively, some pathogens directly invade cells, which then become antigen presenting cells as their cell membranes change. If this occurs the cells are no longer recognised as ‘self’.
Once changed, the antigen presenting cells present their antigen to the B and T cells, and activate the ones that are specific to that antigen
Immune memory "Immunity"
B cells are activated by being exposed to an antigen that combines with its specific antibody
This causes clonal expansion and an exponential growth in the numbers of that specific antibody producing B cell
The ‘daughter’ cells secrete many copies of the antibody
The antibodies help destroy the antigen
Eventually, most of the daughter cells die off
Some persist in the circulation
If re-exposed to the antigen, they can very rapidly reactivate, clonally expand, and produce more antibody
The secondary response is quicker and bigger than the primary response
This is the basis of immunological memory, and immunity

Pathogen
Any micro-organism capable of causing disease
Antigen (Ag)
Any substance or structure that our body recognises as foreign (not ‘self’)
Capable of triggering the acquired immune system
eg protein structure on the cell wall of a bacteria, or viral DNA, or pollen
Antibody
Protein molecules produced by the body in response to an antigenic trigger.
Each antibody produced will only recognise one specific antigen

Pathogens consist of, or display, antigens

The immune system is designed to protect the body from pathogens
Non-specific resistance to infection
Does not confer immunity to specific diseases
Includes physical barriers, chemical agents, white blood cells (of the myeloid line)
Cells - phagocytes
Barriers such as skin, mucous membranes, stomach acid
Competition for nutrients from non-pathogenic (commensal) bacteria in the gut
Actions such as coughing and sneezing
Neutrophils, monocytes and macrophages
Phagocytosis; how a cell ingests and destroys ‘foreign material’ such as viruses and bacteria
Neutrophils and monocytes circulate in blood, macrophages live in tissues such a spleen and lymph nodes
Phagocytosis is the ultimate fate of foreign material, but often needs to be triggered by the acquired (specific) immune system
Cells - antigen presenting cells (eg dendritic cells)
Live in spleen and lymph nodes
Trap pathogens
Present antigens to the cells of the acquired (specific) immune system
Acquired (specific) immune system
The state of heightened immunity or resistance specific to a particular antigen, which is acquired by exposure to that antigen
Has ‘memory’ and can confer immunity to pathogens
Includes white blood cells (of the lymphoid line)
B cells produce antibodies, and are responsible for immune memory (immunity)
T cells are involved in direct pathogen killing, and regulation of the rest of the immune system
Released from the bone marrow, circulate, and develop the ability to recognise a specific antigen (and only that antigen)
They then mature and develop specialist functions and are known as lymphocytes (B cells and T cells)
The majority are in the lymph nodes and spleen, with a small proportion circulating through blood and lymph awaiting exposure to an antigen
There are approx 100,000 – 400,000 lymphocytes in each ml of blood
B cells
Develop the ability to produce antibodies
Through random genetic shuffling, each B cell produces only one type of antibody, which will be specific to only one antigen
The immune system can produce billions of different B cells, producing billions of different antibodies
T cells
Develop T cell receptors unique to each T cell, produced by random genetic shuffling
Each T cell produces only one type of T cell receptor, which will be specific to only one antigen
There are various sub-sets of T cells, each with different functions;
T helper cells and T suppressor cells (CD4 and CD8 cells) regulate the function of the rest of the immune system
Cytotoxic T cells are involved with the destruction of infected cells (eg those containing virus)
Lymphoid stem cells
Innate (natural) immune system
During the maturation process if they have developed to recognise 'self', rather than 'foreign' they are destroyed
Problems with the innate (natural) immune system
Cystic fibrosis
Mucous is an inadequate barrier leading to chronic lung infection/early death
Antibiotic use
Changes normal gut bacteria, reducing competition, allowing the overgrowth of potential pathogens eg C. difficile, Candida
'Inadequate' immune response
'Too much' immune response
Allergy
When the body mounts an inappropriate immune response to an antigen that does not usually cause disease eg peanut, pollen


Auto-immune disease
When the body misrecognises 'self' as 'foreign' and mounts an inappropriate immune response
Full transcript