Immunology (microbiology)

Question 1

What is immunity

Answer 1

Resistance to disease, specifically infectious disease

Question 2

What is the immune system?

Answer 2

The collection of cells, tissues, and molecules that mediate resistance to infections

Question 3

What is the IMMUNE RESPONSE?

Answer 3

The coordinated reaction of these cells and molecules to infectious microbes.

Question 4

What is IMMUNOLOGY?

Answer 4

The study of the immune system, including it’s responses to microbial pathogens and damaged tissues and its role in disease.

Question 5

The most important physiological function of the immune system is to

Answer 5

PREVENT infections and to ERADICATE established infections.

Question 6

Discuss the vaccination and the idea behind vaccination.

Answer 6

Conversely stimulating the immune response against microbes through vaccination is the most effective means of preventing infection.

VACCINATION- A process of induction of immunity to a pathogen by deliberate injection of a weakened , modified or related form of the pathogen which is no longer pathogenic

Question 7

Many inflammatory diseases are caused by an

Answer 7

ABNORMAL immune response.

Question 8

The immune response is the major barrier to successful —- to treat organ failure

Answer 8

organ transplantation

Question 9

The importance of the immune system is illustrated by observation that individuals with defective immune responses are

Answer 9

susceptible to serious life threatening infections.

Question 10

The immune system also prevents the growth of

Answer 10

some tumours.

Question 11

The immune response also participates in the clearance of

Answer 11

dead cells and initiating tissue repair.

Question 12

Diagnostics→ products of the immune cells e.g. antibodies are used in serological tests in order to

Answer 12

diagnose a variety of infections.

Question 13

What is the role of the immune system?

Answer 13

1. Defence against infections
   =Deficient immunity→increased susceptibility to infections
   Vaccination boosts immune defences and protects against infections
2. Defence against tumours
   =Potential for immunotherapy of cancer
3. The immune system responds to tissue grafts and newly introduced molecules
   =Immune responses are barriers to transplantation and gene therapy
4. The immune system can injure cells →induce pathologic inflammation
   =Abnormal immune responses are the cause of allergic, autoimmune and other inflammatory diseases

Question 14

The two types of immunity?

Answer 14

INNATE (NATURAL) IMMUNITY – Mediates the initial protection against infections

ADAPTIVE (ACQUIRED) IMMUNITY – Develops slowly and provides more specialised and effective defence against infections

Question 15

Discuss the path taken by an infectious agent when it first gets into the body.

Answer 15

An infectious agent first encounters elements of the innate immune system. These may be sufficient to prevent disease. But if not , disease results.

The adaptive immune response is then activated to produce recovery. And specific immunologic memory. . Following re-infection with the same agent, no disease results. And the individual has acquired immunity to the infectious agent

Question 16

INNATE (NATURAL) IMMUNITY

Answer 16

Always present in healthy individuals.
Consists of physical /chemical /biochemical properties
Biochemical – lysozyme(tears,nasal secretions, saliva), sebaceous gland secretions, commensal organisms in gut and vagina ,spermine (semen)
Physical /chemical – skin, mucus, cilia lining the trachea, acid in the stomach

Question 17

First line of defence is provided by

Answer 17

epithelial barriers and by cells present in the epithelia

Question 18

LIST THE FIRST LINES OF DEFENCE

Answer 18

1. Saliva - antibacterial enzymes
2. Skin - prevents entry
3. Stomach acid - low pH and kills harmful microbes
4. Tears - anibacterial enzymes
5. Mucus linings- trap dirt and microbes
6. “good” gut bacteria - out compete bad bacteria

Question 19

What are the cells involved in INNATE IMMUNITY?

Answer 19

Cells / soluble factors

Phagocytes
Natural killer cells (specialised lymphocytes)
Dendritic cells
Complement
Acute phase proteins e.g. C - Reactive protein

When cells breach the barrier and enter tissues/circulation they are attacked by phagocytes and specialised lymphocytes called nk cells. In addition the innate immunity also enhances the adaptive immunity.

Question 20

ADAPTATIVE (ACQUIRED) IMMUNITY

Answer 20

This type of immunity has to ADAPT to the presence of microbial invaders.
Therefore requires expansion and differentiation of cells (lymphocytes) before it can provide an effective defence

Question 21

Two types of adaptive immunity

Answer 21

1. Cell-Mediated Immunity (CMI)

2. Humoral immunity

Question 22

1. HUMORAL IMMUNITY

Answer 22

Mediated by proteins called antibodies.
Antibodies are produced by cells called B lymphocytes.
Secreted into circulation, and mucosal fluids.

ROLE: Eliminate microbes and microbial toxins that are present OUTSIDE host cells i.e. they STOP microbes that are present at mucosal sites/blood from invading host cells and connective tissue

These antibodies cannot get gain access to organisms that live INSIDE infected cells (intra-cellular organisms)

Therefore defence against intracellular organisms requires another form of immunity i.e. Cell mediated immunity (CMI)

Question 23

2. CELL-MEDIATED IMMUNITY

Answer 23

Mediated by cells called T-Lymphocytes
Different types of T-lymphocytes e.g. Helper-T-lymphocytes, cytotoxic T- lymphocytes

ROLE:
Eliminate intracellular microbes
Kill infected cells
Eliminate reservoirs of infection

Question 24

What are the features of adaptive immunity?

Answer 24

1. Specificity
   =Ensures distinct responses for specific microbial molecule (antigens)
2. Diversity
   =Enables the immune system to respond to a large variety of antigens
3. Memory
   =Enables rapid and enhanced responses to repeated exposures to the same antigen
4. Non-reactivity to self
   =Prevents injury to host during the response to foreign microbes

Question 25

What is Passive immunity?

Answer 25

Only physiological example – NEWBORNS Their immune systems are not mature enough to respond to many pathogens They acquire antibodies from their mothers via the placenta and breast milk thereby facilitating protection against infections.

Question 26

3 broad groups of cells in the immune system

Answer 26

Lymphocytes Antigen-presenting Cells Effector Cells

Question 27

Antigen -presenting cells - overall function - Different types and their specific functions

Answer 27

Overall function: Capture antigens and display them to lymphocytes 1. Dendritic cells =Capture antigens and transport them to lymph nodes → here they display the antigens to T lymphocytes 2. Macropahges = Phagocytosis of microbes in tissues 3. Follicular dendritic cells =Reside in peripheral lymphoid organs and present antigens to B cells. **B lymphocytes also act as antigen-presenting cells.

Question 28

Effector cells

Answer 28

Overal function: Eliminate antigens 1. T lymphocytes 2. Macrophages /monocytes 3. Granulocytes: neutrophils/eosinophils

Question 29

Lymphycytes - Overall function - Different types and their specific functions

Answer 29

Overall function: Specific recognition of antigens (microbial molecules) 1. B lymphocytes =Mediators of humoral immunity. Neutralize the microbe, Activate complement and Phagocytosis 2. T Lymphocytes i)Helper T =Mediators of cell-mediated immunity Activate macrophages , Inflammation Further activation of B/T Lymphocytes ii) Cytotoxic T (CTL) = Direct killing of infected cell iii) Regulatory T = Suppression of the immune response 3. Natural killer cells =Cells from innate immune system Directly kills infected cells

Question 30

2. T Lymphocytes

Answer 30

i)Helper T =Mediators of cell-mediated immunity Activate macrophages , Inflammation Further activation of B/T Lymphocytes ii) Cytotoxic T (CTL) = Direct killing of infected cell iii) Regulatory T = Suppression of the immune response

Question 31

Tissues of the immune system

Answer 31

1. Generative lymphoid organs 2. Peripheral lymphoid organs 3.

Question 32

1)GENERATIVE LYMPHOID ORGANS

Answer 32

``` Bone marrow ( B lymphocytes) Thymus (T lymphocytes) ``` Here the B and T lymphocytes are allowed to mature and become competent to respond to antigens

Question 33

2) PERIPHERAL LYMPHOID ORGANS

Answer 33

Consists of lymph nodes, the spleen ,mucosal and cutaneous immune systems. Here , adaptive immune responses are initiated

Question 34

Discuss lymph nodes

Answer 34

They are encapsulated nodular aggregates of lymphoid tissue Located throughout the body *Lymph is a fluid that is constantly leaking out of all blood vessels in all epithelia, CT, and most parenchymal organs. This lymph is drained by lymphatic vessels from the tissues to the lymph nodes

Question 35

Discuss the spleen

Answer 35

Highly vascular abdominal organ Responsible for eliminating blood borne antigens The spleen contains abundant phagocytes which ingest and destroy microbes in the blood.

Question 36

Cutaneous immune system and mucosal immune system

Answer 36

Cutaneous immune system =Collection of lymphoid tissues under the epithelia of skin Mucosal Immune system =Collection of lymphoid tissue in the gastrointestinal tracts (Peyer's patches) and respiratory tracts

Question 37

Overview of immune responses to Microbes – sequence of events. From when the microbe enter the system

Answer 37

**Microbe enters 1. Early immune response 2. Adaptive immune response 3. Decline of immune response and memory

Question 38

Principle barriers between host & environment →

Answer 38

1. epithelia(skin), 2. GI and 3. respiratory tracts. These barriers impede entry of microbes **Innate immunity can eradicate some infections and keep other pathogens in check until the more powerful adaptive immune response is activated

Question 39

EARLY IMMUNE RESPONSE

Answer 39

If the microbe traverses the epithelia , they encounter other components of the innate immunity These include phagocytes (which include neutrophils/macrophages ) → ingest microbes into vesicles and destroy them by producing microbial substances. Macrophages and dendritic cells also secrete CYTOKINES → results in INFLAMMATION ( brings leucocytes and other proteins to the site of injury) Important to note that the innate immune system also provides signals that initiate the adaptive immune system

Question 40

The adaptive immune response has distinct immune phases :

Answer 40

a) antigen recognition and capture b) lymphocyte activation c) antigen elimination d) homeostasis and memory

Question 41

a) antigen recognition and capture

Answer 41

Microbes (antigens) that enter the epithelia are captured by dendritic cells (reside in epithelia) They are then transported to draining lymph nodes Inside the dendritic cells the antigens are processed (broken down) into smaller pieces (peptides) The dendritic cells then display the peptides on the surface of the cell → giving rise to the term ANTIGEN PRESENTING CELL (APC) These peptides are then recognized by B and T lymphocytes → initiation of T cell responses (proliferation and differentiation)

Question 42

b) lymphocyte activation + c) antigen elimination

Answer 42

When naïve t lymphocytes are activated by peptides → secrete cytokines (act as growth factors) → results in proliferation and differentiation into effector cells These effector T- cells (generated in lymphoid organs) migrate back into the circulation to the site where the initial microbe (antigen) entered. Here the T lymphocytes serve in various ways to eliminate the organism

Question 43

How are B lymphocytes also Antigen-presenting cells?

Answer 43

B lymphocytes → also differentiate and proliferate in to plasma cells Plasma cells secrete different classes of antibodies which have distinct functions B lymphocytes also ingest the antigens and break them down into peptides → display them on their surface for T lymphocytes to recognize → hence they are also ANTIGEN PRESENTING CELLS **Hereby further activating the T cell responses

Question 44

Discuss how antibodies work

Answer 44

Antibodies bind to microbes and prevent them from infecting cells Antibodies also coat the microbes (opsonize) the microbes and make them targets for phagocytes (macrophages and neutrophils) Antibodies activate complement → Phagocytosis and the destruction of microbes are enhanced

Question 45

d) Homeostasis and Memory

Answer 45

After elimination of the organism majority of the lymphocytes die by apoptosis Thereby returning the immune system to a basal resting state (homeostasis) The initial activation of T lymphocytes generates long-lived memory cells → that survive for years after infection and they mount rapid and robust responses upon encounter with the same antigen

Question 46

IMMUNITY SUMMARY FLASHCARD

Answer 46

1. pathogen recognition and initial attack cells involved are macrophages, neutrophils, natural killer cells, and antigen-presenting cells 2. Transmission of pathogen information to the adaptive immune system via dendritic cells. Moving to lymph nodes. Gets there gives the presented microbe to T-cells and activates them. The activated t-cell interacts with B-cell and activates the b-cell. From activated t-cell, we get cytotoxic t-cells and from activated b-cell, we get Plasma cells and --> antibodies and some memory cells. All lead to: 3. Specific attack on pathogens