Outline the role of skin & mucous membranes Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues Distinguish between antigens & antibodies Explain antibody production

The Body’s Defence Prevents pathogens that have entered the body causing harm Specific vs. Non-Specific Prevents pathogens entering the body Immune system/leucoytes (phagocytotic & lymphocytes) Skin, mucus membranes, various other ‘fluids’ & structures PreventionCure physical and chemical barriers, e.g blood clotting antibodies actively made by the body Both can be artificially acquired

The body’s defence: Non-specific First line of defence: skin Externally covered by keratinised protein of the dead cells - Tough and impervious Folds in skin with moisture can lead to breaking barrier e.g. athlete’s foot Diagram not required

Non-specific immunity: summary Complement system: 20 or so antimicrobial proteins in blood Localised damage – inflammation: increased number of leucocytes. Mast cells secrete histamine which makes blood vessels ‘leaky’ – allowing complement to reach damaged tissue. Blood clotting helps to seal off any wounds.

Phagocytes – Non-Specific Secondary Defence Phagocytes are a type of leucocyte (white blood cell). They recognise the pathogen after it has been coated by an antibody and destroy it

Phagocytes - Phagocytosis v +phagocytosis&Category=Blood+Cells&Group&Section=Introduction

Antibody Production SL What is the difference between an antibody and an antigen?

Antigens vs. Antibodies FOREIGNERS Antigen (Ag)– molecule recognised as foreign by the immune system The outer surface of microbes are covered in antigens Phagocytotic leucocytes may present these on their outer surface RESPONSES TO THEM Antibodies (Ab) – a globular protein that recognises Ag Antibodies are produced by special white blood cells called B-cell (B- lymphocytes) These are formed and matured in the bone marrow but are stored in the lymph nodes, where they come into contact with Ag

SL Identify the antigen and antibody

Structure of an antibody

The blood contains two types of white blood cell or Leukocyte Phagocytes ingest bacteria by endocytosis… Lymphocytes produce antibodies… SL

There are many types of lymphocyte, you do not need to know them… but each has a very specific function within the immune system

CD4 lymphocyte deficiency is associated with AIDS and leads to reduced antibody and ‘killer’ production as this cell helps the others function

Antibodies Proteins that recognise and bind to specific antigens Lock and key system Antigens are foreign substances that stimulate production of antibodies Many molecules on surface of viruses and bacteria are antigens SL

Antibodies are specific – they usually bind to only one specific antigen Millions of different lymphocytes in the body, all with unique complement of antibodies to recognise the antigens Antigen Antibodies Microbe SL Est. a single humans is capable of generating ~10-billion different kinds of antibodies. Each type of antibody defends the body against a specific type of antigen.

Production of Antibodies by Lymphocytes A lymphocyte can produce only one type of antibody so a huge number of different types are needed Each lymphocyte has some of its antibody on its surface… SL

The antigens of a pathogen bind to the antibodies in the surface membrane of a lymphocyte… …This activates the lymphocyte. SL

The active lymphocyte divides by mitosis to produce a clone of many identical cells MITOSIS The clone of cells starts to produce large quantities of the same antibody… … the same antibody needed to defend against the pathogen! SL

Most microbes have more than one antigen on their surface, so… …they stimulate more than one type of lymphocyte… …resulting in the production of many different antibodies which will act against it. These are called polyclonal antibodies. SL

Lymphocyte (B-cell) Macrophage/ Phagocyte Antigen Activate Antigen Lymphocyte (Helper T-cell) Activate Clone Memory Cell Plasma Cell Antibodies Antibody Production: Summary SL

Immunity PacMan! One PACMEN (phagocyte) You can eat things tagged with antibodies Three + opposing pacmen (bacteria) You must be tagged – only then you can be destroyed Three + fruits (lymphocytes) Can tag the bacteria, making them recognisable to pacmen

Immunity Questions 1.What is an antigen? [2] 2.What is an antibody? [2] 3.Where are leucocytes produced? [1] 4.How are antibodies produced? [2] 5.What is a memory cell? [2] 6.What is meant by the ‘specificity’ of the immune response? [2] 7.How do antibodies kill antigens? [2] Marks out of 13:

1.An antigen is a protein on the outside of a foreign cell that can be recognised as ‘foreign’ and can evoke an immune response 2.A protein produced by certain leucocytes (B lymphocytes, plasma cells) in response to a specific antigen 3.In the bone marrow 4.Antibodies are produced by lymphocytes once they have come into contact with a complementary/specific antigen 5.Memory cells are a type of lymphocyte that is produced during the primary/first immune response to an antigen (on a pathogen). They live for years and are responsible for the ‘immunity’ we develop after we have had a disease. 6.Every WBC has a unique complement of antibodies. A specific antibodys only bind to specific antigens, thus a lymphocyte with a complementary antibody must come into contact with the antigen before an immune response happens 7.The complementary ‘arm’ of the antibody binds to an antigen on the surface of a pathogen. Antibodies coat the pathogen, directly killing it or ‘tag’ it for phagocytosis/ ingestion by a phagocyte. Immunity Answers

Immunity

Whiteboard Quiz Question & Answer Crash course biology (15 mins) Immunity multiple choice: 1.A 2.B 3.D 4.B 5. C

SL

Higher Level Details

Antibody Production: The Primary Response Macrophages take in antigen by endocytosis Antigen Macrophage The macrophage processes the antigen and attaches it to a membrane protein called a MHC protein The MHC protein is moved to the cell surface membrane by exocytosis so that the antigen is displayed on its surface. MHC protein Step 1: Antigen Presentation

Helper T-cell binds to macrophage presenting the antigen Step 2: Activation of Helper T-cell Helper T-cells have receptors on their cell surface membranes which can bind to antigens presented by macrophages. receptor Helper T-cell Macrophage sends a signal to activate the helper T-cell

Step 3: Activation of B-lymphocytes B-cells have antibodies in their cell surface membranes Inactive B-cell Antibody Antigens bind to the antibodies in the surface membranes of B-cells Antigen

An activated helper T-cell with receptors for the same antigen binds to the B-cell SIGNAL The helper T-cell sends a signal to the B-cell, activating the B-cell.

Step 4: Proliferation Plasma cells are activated B-cells with a very extensive network of rough endoplasmic reticulum. Plasma cells synthesis large amounts of antibody, which they excrete by exocytosis. The activated B-cell starts to divide by mitosis to form a clone of plasma cells.

The Secondary Response: Memory Cells If an antigen invades your body a second time, a much faster response occurs which produces much larger quantity of the required antibody. When activated B-cells are dividing during the primary response, some cells stop dividing and secreting antibody and become memory cells. Large numbers of memory cells remain in the body for a long time… …they are capable of producing large amounts of antibody very quickly when stimulated.

B-cell Macrophage Antigen Activate Antigen Helper T-cell Activate Clone Memory Cell Plasma Cell Antibodies Antibody Production: Summary