The Immune System

The First Line of Defence

barriers that prevent pathogens from entering the body.

The Second Line of Defense

involves the action of leukocytes when a pathogen invades the body. Respond is rapid and the same no matter what the pathogen is.

Physical barriers

physical block against pathogens from entering the body.

E.g. intact skin, mucous membranes of internal body linings, flushing of urine

Chemical barriers

to destroy pathogens on the outer body surface at body openings and on inner body linings.

E.g. stomach acid, enzymes in saliva, mucous and tears kills or inhibits growth of microbes.

Biological barriers

residential flora living on the surface of epithelial tissues.

prevents microbes from reaching tissues that are susceptible to infection.

Phagocytosis

Inflammatory response

results in swelling, redness, heat and pain.

1. Histamines released by mast cells as well as cytokines promote vasodilation. Means more blood can flow to the site of damage.

Macrophages

develop from monocytes that migrate into tissues

-present in almost every tissue of the body

Neutrophils

-first to site of infection

-found in blood

Mast cells

-found in epithelial tissues close to external environment

-release histamine

-allergic response

2. Histamines also cause the walls of capillaries to become more permeable. Leukocytes, blood plasma and blood proteins can move into site of infection. Causes swelling and puts pressure on surrounding tissue which causes pain.

3. Cytokines stimulate the movement of neutrophils to the affected area. Monocytes then arrive which mature into macrophages, engulf and destroy pathogens.

Humoral Innate Immunity

Complement System

group of more than 30 different proteins dissolved in blood plasma that consist of chemical reactions that have three pathways.

Opsonisation

Chemotaxis

Osmotic cell lysis-membrane attack complex

Interferons

group of proteins (type of cytokine) released by body cells that are infected with a virus.

-Important if the virus gains entry to the body close to its target cell.

Third Line of Defense

adaptive immune response to a specific pathogen inside the body that helps to build immunity

Cell-mediated

-a specific response that aids in defense against cells infected with viruses, cancerous cells and transplanted tissue.

Humoral

-involves the action of B cells and production of antibodies secreted in body fluids or "humours"

T-lymphocytes

-mature in thymus migrate to lymph nodes

-activated by exposure to antigens on APCs

Lymphatic system

Immunocompetency tests

-Cells that recognize self antigens or fail to respond to non-self antigens are eliminated by apoptosis.

Primary lymphoid organs

T cells- thymus, B cells-bone marrow

Memory cells

Long lived lymphocytes that have the ability to remember previous antigens to which it has responded and that on re-exposure rapidly initiates the immune response.

Secondary lymphoid organs

Lymph nodes

-filter and trap foreign material

-lymph nodes become swollen when fighting an infection b/c WBCs are multiplying rapidly inside

-APCs migrate to lymph nodes to "present" antigens to lymphocytes.

-Clonal selection of B lymphocytes

B Lymphocytes

-matures in bone marrow

-APC

Clonal Selection and Expansion

1. Clonal selection

-in lymph nodes, an antigen binds to a specific antibody molecule on surface of B cell which is selected from a pre-exisiting cell pool containing different receptors

2. Clonal Expansion

-A T helper cell must bind to the selected B cell, releasing cytokines causing proliferation and differentiation of cells resulting in large numbers of B cells that all have the same receptors. Differentiate into either memory or effector cells.

Plasma cell

produce large numbers of antibodies against a particular pathogen.

Memory B cell

-remembers the same pathogen for faster antibody production in future infection, often attacking pathogens before symptoms occur.

Antibodies

-proteins produced by animals in response to antigens and which react specifically with the antigen that induced their formation.

-made up four polypeptide chains, two heavy and two light. They have a constant region and a variable region. At the tip of the variable region is the antigen binding site.

Memory T cells

-survive for many years and proliferate rapidly into Th and Tc cells when the body is exposed to the pathogen for a second time.

Helper T cell

-secrete various cytokines that help activate B cells to differentiate and proliferate, phagocytes and cytotoxic T cells.

Cytotoxic T cells

-play a major role in host defense against virally infected or cancerous cells.

-release cytotoxins including perforin and granzymes. Perforin inserts into the plasma membrane and creates pores. Granzymes enter through the pore and initiate apoptosis.

Effects of antibodies

1. Neutralisation

-binds to surface of pathogen that prevents it from binding to healthy body cells

2. Activation of complement cascade

-bind to surface and tag pathogen for destruction by signaling complement cascade

3. Opsonisation

-coat pathogen for easy detection and uptake by phagocytes

4. Agglutination

-antibodies stick together in a pathogen-antibody net. prevents spread of pathogens.