Immune System
Cell Recognition
Lymphocytes bump into body cells at birth,and those that fit, will be destroyed or suppressed (Apoptosis).
The remaining lymphocytes with then recognise the non-self cells and cause a immune response
In adults, lymphocytes are produced in the bone marrow
Phagocytosis (Non-Specific)
Phagocytes = White blood cells that respond to non-self cells
Some travel in the blood, some in other tissues
Detects chemicals released by the pathogen, moves towards it up the concentration gradient.
Receptors on the cell-surface membrane attach to the antigens from the pathogen
Lysosomes migrate towards the pathogen as the phagocyte engulfs it
The lysosomes release their lysosymes into the pathogen and becomes hydrolysed
The products from the pathogen are absorbed by the phagocyte
Lymphocytes (Specific)
Produced by stem cells in the bone marrow
B and T lymphocyte
B lymphocytes - Mature in the bone marrow and to do with humoral immunity
T lymphocytes - Mature in the thymus gland and to do with cell-mediated immunity
Cell-Mediated Immunity
T lymphocytes can distinguish the non-self cells by the antigens on the surface of the cell-surface membrane (CSM)
Antigen-presenting cells can present foreign antigens of other cells on its own cell-surface membrane
T Cells only respond to antigens presented on the surface of the cell
Pathogens invade host, phagocyte places antigens from the pathogen on its own CSM, this fits exactly onto receptors on the T cells + causes the T cells to undergo mitosis.
These T cells can 1. Develop into memory cells for a future infection. 2. Stimulate phagocytes to engulf pathogens. 3. Stimulate B cells to divide + secrete antibodies. 4.Activate cytotoxic T cells (Tc)
Tc cells kill abnormal cells by producing perforin (protein) that makes holes in the CSM, making the cell permeable to all substances + dies. Most effective against viruses
Antibodies
Humoral Immunity
As many as 10M different B cells, each produce a specific antibody
Antigens are complementary to one of the B cells and enters the B cell by endocytosis + gets presented on the surface
Helper T cells (Th) bind to these antigens and stimulate B cells to divide by mitosis to produce an antibody complementary to the antigen
Clonal Selection
Each cloned antibody is called a monoclonal antibody
Develops into two types of cells: Plasma cells and Memory cells
Plasma cells secrete antibodies into the blood plasma, they survive for a few days and make up to 2000 antibodies every second. They are used as an immediate defence against infection (Primary Immune Response)
Memory cells (Secondary Immune Response) live much longer and divide rapidly if the same antigen is present into plasma cells and more memory cells. Leading to long-term immunity. This is a much faster response and prevents any harm
Protein with a specific tertiary structure to one complementary antigen
Made from 4 polypeptide chains, long (heavy chains) and short (light chains)
Join up to antigens to form Antibody-Antigen complex (AAC)
Active site is called the variable region
Rest of antibody is called the constant region
Cause agglutination of bacteria cells, making it easier to be engulfed and located.
They act as markers that stimulate phagocytes to engulf the bacteria cells
Monoclonal antibodies are made able to attack specific antigens such as cancer cells to block cell growth
Monoclonal antibodies can also diagnose different diseases and pregnancy
Monoclonal antibodies have some ethical issues such as the use of mice and may cause some deaths and organ failure if done wrong
Vaccination
Passive Immunity
No direct contact with the pathogen
No memory cells are formed
Antibodies aren't replaced when used
Eg. Anti Venom and antibodies from the placenta
Active Immunity
Produced by stimulating the production of antibodies by their own immune system
Takes time to develop
Natural results from contact directly from active pathogens
Artificial forms from vaccinations, without any symptoms
Stimulates an immune response, causing memory cells to be made
Needs to be economically available, few side effects, able to be stored and transported, easy way to administer it and can create herd immunity
Ethical issues
HIV
Human Immunodeficiency Virus
Leads to Acquired Immune Deficiency Syndrome (AIDS)
Outside is a lipid envelope, embedded with attachment proteins
Inside is a capsid containing RNA and enzymes (Reverse Transcriptase)
Called a retrovirus - It converts DNA to RNA
HIV binds to a protein called CD4 on the helper T cells.
Capsid fuses with CSM and the RNA+enzymes enter the cell
HIV reverse transcriptase converts the virus's RNA to DNA and moved into the cell
The HIV DNA creates mRNA to make new HIV particles
The HIV particles move out of the Th cell with a piece of its CSM to make the lipid envelope
ELISA test, uses antibodies, to test quantity too
Normal amount of Th cells =800 to 1200 per mm^3, Someone with HIV = 200 per mm^3
Antibiotics
Work by weakening the cell wall of bacterium by inhibiting the metabolic processes of forming the cell wall's strength
As viruses lack metabolic processes, antibiotics cannot work