The First Line of Defence

The First Line of Defence

The first line of defence consists of physical and chemical barriers to prevent the entry:

Skin Mucus Cillia Chemical barriers and Other bodily secretions

4.2 identify antigens as molecules that trigger the immune response

Anti = Antibody -gen = generator

Antigens on a bacterium

Antigens are often part of the outer coating of a bacterium or virus. Theantigen is recognised by the body as not being part of itself, andantibodies are released to attach to the antigen.

The Second Line of Defence

Inflammation responseIf a pathogen (eg bacteria) is successful in penetrating the first line barriers, injured cells let off a chemical alarm such as histamines.

Inflamation- This causes blood vessels to dilate, increasing blood flow to the area, and increasing the permeability of the vessels.

The area becomes swollen, red and painful.

The lymphatic system returns intercellular fluid to the blood system, filters cell debris and produces white blood cells responsible for the immune response.

Includes: Spleen, thymus, tonsils and lymph nodes and vessels.

Lymphatic System

Some white blood cells, called macrophages and neutrophils, can very easily change their shape so that they flow around particles and completely enclose them within their cell, where they are broken up by cell enzymes. This is called phagocytosis.

Phagocytosis

Animation - Phagocytosis http://www.youtube.com/watch?v=VAhM9O

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For some pathogens, macrophages and lymphocytes completely surround a pathogen so that it is enclosed in a cyst. The white cells involved die so that the pathogen is isolated from its food supply and also dies.

Cell death to seal off pathogens

identify the components of the immune response:—antibodies—T cells—B cells

3rd Line of Defence

AntibodiesAntibodies are proteins, calledimmunoglobulins, which are producedin response to the presence of anantigen in the body.

When the appropriate B cells are activated they form plasma cells that produce antibodies, the antigen binding sites of which match the shape of the antigen they are specific for. These antibodies then seek out the antigen and bind to a part of it, forming the antigen–antibody complex, which causes the deactivation of the antigen.

There are a number of ways in which the antigen can be destroyed, including - immobilising it, blocking and neutralising the active binding site of the antigen, or by causing the antigen– antibody complex to clump together, making them easier to eliminate by phagocytosis.

B cell T cell

Cancer cell

T cell

- Another type of lymphocyte.- Differentiate in thymus gland.- Thus ‘T cell’.- Remain inactive in blood & lymph until

they detect an antigen.- Antigen binds to T cell, activating cloning

mechanism.- T cells control cell-mediated response.- Various types of T cells destroy antigen /

foreign cell.

Cytotoxic T cells:- Carry antigens.- Remove foreign proteins

from body.- Anything recognised as

‘non self’.- Bacteria.- Transplants.

Natural killer cells:- Special cytotoxic T cells.- Destroy abnormal host

cells.Eg. Cancer cells, viruses.

Helper T cells:- Secrete interleukins.- Regulate cytotoxic T cell &

B cell functions.- Inducer T cells, suppressor

T cells:- Regulate T & B cells.- Start & stop production and

action.

Memory T cells:- Recognise antigen when

reappearing.- Have helper T cell function.- Quick supply of antibody to

antigen.

Immune Response - Antigen enters body.- Travels via blood to lymphoid tissue (lymph node

or spleen).- Ingested, processed by macrophage.- Displays fragments of antigen on outer

membrane.- Recognised by helper T cells & B cells.- Interact through cytokines (secreted by T cells &

macrophages)- Signal other cells to initiate immune response.Eg. B cell to transform into plasma cell.

Interaction between B & T lymphocytes:- Attack same antigen.- ‘Helper T cells’ stimulate B & T cells to clone.

Mechanisms2 proposed mechanisms for interaction of B & T cells.

Mechanism 1:- T cell produces soluble factor after interaction with

antigen.- B cell reacts with factor & specific antigen.- B cell becomes functional antibody producing cell.

Mechanism 2:- Based on cell contact between T & B cell.- Contact arises from interaction with antigen.- Contact allows T cell to signal B cell to become

functional.- Antibody producing cell.

Collaboration of Cells- Close to each other.- Regulated by cytokines.

- Proteins/polysaccharides.- Secreted by T cells & macrophages.- Signal other cells to initiate immune response.

Mechanisms allowing interaction of B & T lymphocytes:

- T lymphocytes help B lymphocytes.- Helper T cells (Th cells).- If B cell has antigen on surface, risk that T cell will

recognise antigen & attack it & B cell.- T cell able to recognise ‘self’ molecules.

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Cell-mediated response

Antibody-mediated response

Just be thankful he’s not you teacher!