Specific Defences

What are specific defences?

those directed towards a particular pathogen

• e.g. COVID vaccine creates COVID antibodies, only attack COVID virus

What is the immune response?

Homeostatic mechanism

What causes an immune response?

foreign pathogen invades

causes immune response which restores internal enviroment

What cells are involved in the immune response?

• B-cells

• T-cells

Where are lymphocytes produced and how are B and T cells subsequently produced

Produced in bone marrow.

T-cells: lymphocytes mature in the thymus

B-cells: lymphocytes mature in the bone marrow

When B and T cells mature, where do they go?

into the lymphoid tissue

• in lymph nodes, spleen, tonsils

What immune response results in the production of B-cells?

• humoral response/antibody-mediated immunity

• B-cells circulate body + attack invading agents

What immune response results in the production of T-cells?

• cell mediated response

• T-cells destroy invading agents

What is an antigen?

any substance capabale of causing the specific immune response

e.g. virus particles, toxins, proteins, egg whites, etc.

What immune response is triggered by antigens?

anitbody-mediated and cell mediated immunity triggered

What is an antibody?

• Y-shaped specialised proteins

• produced by plasma cells

• respond to non-self antigens

What protein group do antibodies belong to?

• immunoglobulins

  • represented by ‘Ig’

  • 5 classes: IgA, IgD, IgE, IgG, IgM

How do antibodies combine with antigen? What is this complex called?

lock and key model (specific antigens and antibodies)

antigen-antibody complex

How do antibodies work?

• inactivate foreign enzymes/toxins by combining with or inhibiting reaction with other cells/compounds

• bind to viruses (prevent entry into cells in the body)

• coat bacteria (makes it easier to be engulfed by phagocytes)

• aggulation (foreign blood cells, viruses, etc. clump together

• dissolve organisms

• react with soluble substances making these substances insoluble (making it easier to be consumer by phagocytes)

What are antigen-presenting cells?

• special cells (dendritic cells, macrophages, undifferentiated B-cells)

• detect invaders (viruses, bacteria, etc.)

  • show pieces of invaders to other immune cells (allow body to attack)

How do antigen-presenting cells work?

1. detect

2. engulf

3. digest (make cell fragments)

4. move fragments to cell surface

5. present fragments to lymphocytes

Outline the steps of the Antibody-mediated response (humoral immunity)

1. Antigen-presenting cells recognise, engulf and digest pathogens, displaying the antigen on their surface.

2. Antigen-presenting cells reach lymphoid tissue and present the antigen to lymphocytes.

3. Helper T-cells are stimulated by antigenpresenting cells, which release cytokines.

4. Specific B-lymphocytes are stimulated to undergo rapid cell division.

5. Most new B-cells develop into plasma cells, which produce antibodies and release them into blood and lymph.

6. Antibodies combine with the specific antigen and inactivate or destroy it.

7. Some of the new B-cells form memory cells.

Outline the steps of the Cell-mediated response (cellular immunity)

1. Antigen-presenting cells recognise, engulf and digest pathogens, displaying the antigen on their surface.

2. Antigen-presenting cells reach lymphoid tissue and present the antigen to the lymphocyte.

3. Helper T-cells are stimulated by antigenpresenting cells, which release cytokines.

4. Specific T-lymphocytes are stimulated to undergo rapid cell division.

5. Most new T-cells develop into killer T-cells or helper T-cells, which migrate to the site of the infection.

6. Killer T-cells destroy the antigen, while helper T-cells promote phagocytosis by macrophages.

7. Some sensitised T-cells form memory cells.

What do killer T-cells do?

• migrate to infection site

• attach to the invading agent

• secrete chemical to destroy anitgen

What do helper T-cells do?

• bind to antigen on antigen-presenting cells stimulating secretion of cytokines

• cytokines:

  • attract lymphocytes (to infection site) which become activitated, intensifying response

  • attract macrophages to site, destroy antigens (phagocytosis)

  • intensify phagocytic activity of macrophages

  • promote action of killer T-cells

What do suppressor T-cells do?

• act when immune response activity is excessive or dealt with successfully

• release substances that inhibit T-cell and B-cell activity

• slows immune response

What is the point of cell-mediated immunity?

Provide resistance to intracellular phase (invaded and replicating in host cells) of bacterial/viral infections.

Fight whole cells (fungi, parasites, cancer cells)

What is the point of antibody-mediated immunity?

• production and release of antibodies into blood and lymph

• provides resistance to viruses, bacteria, etc.

What are the types of immunity?

• natural immunity

• articifical immunity

• passive immunity

• active immunity

What is natural immunity?

• no human intervention

• passive or active

What is artifical immunity?

• giving a person an antigen or antibody

• passive or active

What is passive immunity?

• person recieves antibodies produced by someone else, individuals body plays no part inn production of antibodies

• naturally

  • e.g. baby through breast milk from mother

• artifically

  • e.g. person injected with particular antibodies (such as rabies, tetanus, etc.)

• short-lived (until anti-bodies broken down and excreted)

What is active immunity?

• personn manufactures antibodies in response to foreign antigen

• lasts longer than passiv immunity (memory cells)

• naturally

  • previously having disease

• artificially

  • vaccines (e.g. flu vaccine, COVID vaccine)