Bio 2025 Term 2 - Set 2

1st Line of Defence - Physical and Chemical Barriers

• First line of defence = physical barriers and the immune system defend the body against pathogens

  • Examples of physical barriers - eyelashes, hairs, stomach lining, esophogus (throat) lining, nose hairs

• Non-specific - the purpose of this line of defence is to STOP microbes from entering the body

• Physical barrier - the skin and mucous membranes act as a barrier to PREVENT penetration by microbes

2nd Line of Defence - Inflammation, phagocytosis, fever

• If microbes do manage to get inside the body then the second line of defence is activated

• This is also non-specific as it stops any type of microbe

• This is the line of defence that has attacking cells and molecules which attack pathogens that manage to breach the first line of defence

• Innate responses are non-specific in all animals, are fixed responses, and do not created

Innate & Adaptive Response

• The innate immune response functions as the second line of defence against infection = non-specific

• The adaptive immune response is slower to develop, but manifests as increased antigenic specificity and memory. This is the third line of defence = specific

2nd Line of Defence - Inflammation

• A pathogen stimulates an increase in blood flow to an infected area

• Blood vessels in the area expand - vasodilation

• White blood cells leak into the tissue from the vessels to invade the infected tissue

• WBC (phagocytes) can then engulf and destroy bacteria

• This all causes a red, swollen, painful inflammatory response

2nd Line of Defence - Fever:

• Increased temperatures enhance a variety of immune cells functions

• These include phagocytosis and reactive oxygen species production by neutrophils, as well as enhanced function of natural killer cells, T-helper cells and antibody-producing cells

• Fever can induce heat-shock proteins in both pathogens and host cells

2nd Line of Defence - Phagocytosis

• Is a cellular process for ingesting and eliminating particles larger than 0.5 μm in diameter, including microorganisms, foreign substances, and apoptotic cells

1. Initial contact occurs between phagocytes and pathogen

2. Phagocyte engulfs the pathogen

3. Pathogen is enclosed within the cytoplasm in the phagocyte

4. A lysosome (filled with hydrolytic enzymes) fuses with the engulfed pathogen

5. The enzymes digest the pathogen. The digested parts are released

6. The antigen is presented on the plasma membrane.

3rd Line of Defence - Specific Immunity

• Specific defence processes = the immune responses 'specifically' designed to combat particular microorganisms

• Specific Defences:

  • In specific defences, the immune system forms a chemical "memory" of the invading pathogen

  • If the pathogen is encountered again, the body reacts so quickly that few or no symptoms are felt

  • Specific defences are those that give us immunity to certain diseases

Major Players in the Immune System

• Macrophage

• T cells (helper, cytotoxic, memory)

• B cells (plasma, memory)

• Antibodies

Role of B cells in defending the body

• Protect you from infection by making proteins called antibodies

• B cells are a type of white blood cell called lymphocytes

• When your immune system detects antigens - markers that indicate a threat like a bacteria or virus has entered your body - your B cells produce antibodies to fight the invader

• Plays a role in the third line of defence

• B cells are produced and mature in the bone marrow

Role of T cells in defending the body

• Destroys harmful pathogens and sends signals that help control your immune system's response to threats

• T cells are a type of immune cell

• T cells are a type of white blood cell

• When they sense an infection, they activate other immune cells to fight it

• May activate cytotoxic T cells or B cells

• Plays a role in the third line of defence

• The T cells help identify pathogenic cells and destroy targeted cells

• T cells are produced in the thymus

Define antibody, antibiotic, and antigen

Antibody - a protein produced by the human immune system to tag and destroy invasive microbes

Antibiotic - various chemicals produce by certain soil microbes that are toxic to many bacteria. Some we use as medicines

Antigen - any protein that our immune system uses to recognise "self" vs "not self"

Process(?)

• Humoral immunity produced antigen specific antibodies and is primarily driven by B cells

• Cell-mediated immunity on the other hand does not depend on antibodies for its adaptive immune functions and is primarily driven by mature T cells, macrophages and the release of cytokines in response to an antigen

• Macrophage is a type of blood cell

• Cytokine - chemical messengers

• Plasma cells help by producing antibodies rapidly

• Memory B cells remember what has come into the body for the future

• Cytotoxic T cell doesn't need anything other than itself

  • Destroys the infected cell

B cells

• B-cells in general produce antibodies

• Those with antibodies bind with the invader’s antigen

• B-cells differentiate into either plasma cells or memory B-cells

• Plasma cells rapidly produce antibodies

• Memory cells retain the “memory” of the invader and remain ready to divide rapidly if an invasion occurs again

Role of Antibodies - receptors & effectors

• Antibodies are assembled out of protein chains

• There are many different chains that the immune system assembles in different ways to make different antibodie

• Antibodies may disable some microbes, or cause them to stick together (agglutinate)

• They "tag" microbes so that the microbes are quickly recognised by various white blood cells

• Antibodies released into the blood stream will bind to the antigens that they are specific for

• Antibodies as Receptors:

  • Antibodies can attach to B cells and serve to recognise foreign antigens

• Antigens as Effectors:

  • Free antibodies can bind to antigens, which "tags" to the antigen for the immune system to attack and destroy

Helper T cell

• Helper T-cells have receptors for recognizing antigens

• If they are presented with an antigen, they release cytokines to stimulate B-cell division

• The helper T-cell is the key cell to signal an immune response

• If helper T-cells are disabled, as they are in people with aids, the immune system will not respond

Cytotoxic T cells (“Killer” T cells)

• While B-cells divide and differentiate, so do T-cells

• Some T-cells become cytotoxic, or “killer” T-cells

• These T-cells seek out and destroy any antigens in the system, and destroy microbes “tagged” by antibodies

• Some cytotoxic T-cells can recognize and destroy cancer cells

Calling a halt

• When the invader is destroyed, the helper T-cell calls a halt to the immune response

• Memory T-cells are formed, which can quickly divide and produce cytotoxic T-cells to quickly fight off the invader if it is encountered again in the future

State the difference between bacteriostatic and bactericidal

• Bacteriostatic: antibiotics that inhibit bacterial growth

• Bactericidal: antibiotics that kill bacteria

State the difference between broad and narrow spectrum antibiotics

• Broad spectrum: target many types of bacteria; taken to prevent possible infection after a person has had an operation, or before the species of bacteria has been determined

• Narrow spectrum: target only a few types of bacteria; taken usually when antibiotic resistance bacteria is present/the exact species of bacteria has been determined of the infection

Describe how antibiotic resistance can be transferred by vertical or horizontal gene transfer

• Horizontal evolution (gene transfer):

  • Conjugation: resistance genes can be transferred between bacteria of the same or different species (join together, one donates plasmid)

  • Transduction: resistance genes are transferred from one bacteria to another through viral phage

  • Transformation: resistance genes from live or dead bacteria are picked up by another

• Vertical evolution:

  • Resistance traits are inherited from one generation to another (binary fission)

  • Bacteria undergoing binary fission and over generations, mutations can occur

  • Mutations may be advantageous for bacteria