chapter 12 p4 Flashcards
What is Cell-mediated immunity:
In cell-mediated immunity, T lymphocytes respond to the cells of an organism that have been changed in some way, for example by a virus infection, by antigen processing or by mutation (for example cancer cells) and to cells from transplanted tissue.
The cell-mediated response is particularly important against viruses and early cancers.
Steps in Cell-mediated immunity:
- In the non-specific defence system, macrophages engulf and digest pathogens in phagocytosis.
They process the antigens from the surface of the pathogen to form antigen-presenting cells (APCs). - The receptors on some of the T helper cells fit the antigens.
These T helper cells become activated and produce interleukins, which stimulate more T cells to divide rapidly by mitosis.
They form clones of identical activated T helper cells that all carry the right antigen to bind to a particular pathogen. - The cloned T cells may:
develop into T memory cells, which give a rapid response if this pathogen invades the body again
produce interleukins that stimulate phagocytosis
produce interleukins that stimulate B cells to divide
stimulate the development of a clone of T killer cells that are specific for the presented antigen and then destroy infected cells.
Humoral immunity:
- In humoral immunity the body responds to antigens found outside the cells, for example bacteria and fungi, and to APCs.
- The humoral immune system produces antibodies that are soluble in the blood and tissue fluid and are not attached to cells.
- B lymphocytes have antibodies on their cell-surface membrane (immunoglobulin M or IgM) and there are millions of different types of B lymphocytes, each with different antibodies.
- When a pathogen enters the body it will carry specific antigens, or produce toxins that act as antigens.
- A B cell with the complementary antibodies will bind to the antigens on the pathogen, or to the free antigens.
- The B cell engulfs and processes the antigens to become an APC
Steps in Humoral immunity:
Activated T helper cells bind to the B cell APC.
This is clonal selection - the point at which the B cell with the correct antibody to overcome a particular antigen is selected for cloning.
Interleukins produced by the activated T helper cells activate the B cells.
The activated B cell divides by mitosis to give clones of plasma cells and B memory cells - This is clonal expansion.
the primary immune response in humoral immunity
Cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to the antigens and disable them, or act as opsonins or agglutinins.
it can take days or even weeks to become fully effective against a particular pathogen.
This is why we get ill - the symptoms are the result of the way our body reacts when the pathogens are dividing freely, before the primary immune response is fully operational.
the secondary immune response in humoral immunity
Some cloned B cells develop into B memory cells.
If the body is infected by the same pathogen again, the B memory cells divide rapidly to form plasma cell clones.
These produce the right antibody and wipe out the pathogen very quickly, before it can cause the symptoms of disease.
Autoimmune diseases:
- when the immune system stops recognising ‘self’ cells and starts to attack healthy body tissue.
- There appears to be a genetic tendency in some families, sometimes the immune system responds abnormally to a mild pathogen or normal body microorganisms and in some cases the T regulator cells do not work effectively.
- There are around 80 different autoimmune diseases that can cause chronic inflammation or the complete breakdown and destruction of healthy tissue.
- Immunosuppressant drugs, which prevent the immune system working, may be used as treatments but they deprive the body of its natural defences against communicable diseases.
Chapter 12.7 - Preventing and treating disease
Non-communicable diseases cannot be passed from one person to another.
They include heart disease, most types of cancer and many diseases of the nervous, endocrine and digestive systems.
Communicable diseases are caused by pathogens and can be passed from person to person.
When you come into contact with a foreign antigen, you need some form of immunity to prevent you getting the disease.
There are several ways of achieving this immunity.
Natural immunity:
forms of immunity occur naturally in the body:
When you meet a pathogen for the first time
The immune system of a new-born baby is not mature
When you meet a pathogen for the first time
When you meet a pathogen for the first time, your immune system is activated and antibodies are formed, which results in the destruction of the antigen
The immune system produces T and B memory cells so if you meet a pathogen for a second time, your immune system recognises the antigens and can immediately destroy the pathogen, before it causes disease symptoms.
This is known as natural active immunity. It is known as active because the body has itself acted to produce antibodies and/or memory cells.
The immune system of a new-born baby is not mature
- and it cannot make antibodies for the first couple of months.
- A system has evolved to protect the baby for those first few months of life.
- Some antibodies cross the placenta from the mother to her fetus while the baby is in the uterus, so it has some immunity to disease at birth.
- The first milk a mammalian mother makes is called colostrum, which is very high in antibodies.
- The infant gut allows these glycoproteins to pass into the bloodstream without being digested.
- So within a few days of birth, a breast-fed baby will have the same level of antibody protection against disease as the mother.
- This is natural passive immunity and it lasts until the immune system of the baby begins to make its own antibodies.
- The antibodies the baby receives from the mother are likely to be relevant to pathogens in its environment, where the mother acquired them.
Case Study: Influenza: p2
Every year the mixture of flu antigens in the vaccine is different, reflecting the forms of the virus that the World Health Organisation (WHO) predicts will be most common and most likely to cause serious disease.
If a flu epidemic begins, more people are vaccinated to control infection rates.
Because people travel freely and frequently, an epidemic can spread rapidly from one country to another.
People across the world need to be vaccinated to stop the spread of disease and stock piles of vaccines are in place in case this becomes necessary.
SARS was a new flu-like disease that appeared in 2002 and spread from birds to people. It spread rapidly across countries as people travelled around.
However, in spite of a lack of vaccine, careful management of cases by isolation meant the outbreak was contained and quickly closed down with relatively few deaths (Figure 3).
