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Medicine 1 - 10 Blood and Immunity > 4 How the body responds to infection > Flashcards

4 How the body responds to infection Flashcards

1
Q

What is the human immune system?

A

The defensive mechanisms that identify and neutralise these threats
- it is able to distinguish ‘nonself’ organisms and molecules form ‘self’

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2
Q

What are some potential threats that may enter the body?

A

From the outside
- infectious organisms
toxic agents

Potentially harmful changes occurring within the body
- malignant transformation of a previously normal cell to cancer cell

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3
Q

What are the 3 layers of defence?

A
  1. Barriers
    - Mechanical - skin
    - Chemical (e.g. acidic environment in the stomach)
    - Biological (microbes, flora)
  2. Innate immune system
  3. Adaptive immune system
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4
Q

List the main properties of the innate immune system

A
  • A limited number of hardwired pattern recognition receptors (PRR)
  • Respond rapidly
  • Common to all individuals
  • No memory
  • Class physical/chemical barriers here too
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5
Q

List the main properties of the adaptive immune system

A
  • Enormous variety of somatically generated receptors, generated by gene rearrangement
  • Response slowly on 1st contact (primary)
  • Immunological memory specific to individuals
  • Produces long-lived cells that persist in a dormant state
  • But can re-express effector functions rapidly after another encounter with a specific antigen
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6
Q

What is the most common source of human infections?

A
  • Human infections in infected humans

some:

  • animal reservoirs
  • soil organisms
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7
Q

Describe Major routes of infection and physical barriers

A
  • Aerosol in the respiratory tract
  • Direct mucosal contact - important in STIs
  • Gut pathogens
    > excreted in faeces, and enter the same way
    > or via contamination of water or food (faecal-oral route)
  • Blood to blood
    > exposure to blood, exposure to infected anthropoid (malaria)
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8
Q

How is infection prevented from an aerosol source?

barrier

A

Respiratory tract epithelium has:

  • Mucus secreting cells
  • and cilia

Cilia is are tiny hair-like structures that beat in a synchronous fashion

  • to move particles up the respiratory tract
  • mucociliary clearance

The mucus then traps particles and organisms

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9
Q

Describe the innate immunity in the eye?

and barriers?

A

The eye must be transparent
- and be able to transmit light without distortion

Eye’s defences include:

  • nerve reflex to close the eyelids as danger approaches
  • lacrimal gland to secrete teras to wash particles and pathogens away

The tears

  • contain lysosomes
  • an enzyme that can degrade the bacterial cell wall
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10
Q

Describe how infection is prevented from an ingested source

A
  • HCl and enzymes in the stomach
  • it secretions of the small intestine

Their main role is digestive (and can be harmful to many microorganisms)

The gut has a layer of protective mucosa

  • IgA made specifically for the lining of the gut
  • disables many bacteria and organisms

The gut is not sterile

  • colonised by peaceful fauna that co-exists
  • unless something upsets this balance
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11
Q

Describe the requirements for recognition and defence function in the immune system

And how it can achieve this

A

The requirement is to prevent morbidity and mortality from infection

Three general approached to prevent death and disease:

  • Isolate organism (granuloma in TB)
  • Disrupt organism (physically damaged membrane, or in cancer; activation of apoptosis; natural killer cells)
  • Consume organism (phagocytosis of bacteria by macrophages)

The requirement is to clear pathogens or non-self cells

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12
Q

List the main cellular and secreted mediators of immunity

A
  • Nitric Oxide - inflammation
  • Cytokines (TNF, IL-1)
  • Adhesion molecules for neutrophils and monocytes (selectin) - inflammation
  • Reactive oxygen species (ROS, e.g. peroxide) - defence
  • Antimicrobial peptides (defensins) - defence
  • Chemokines (activate neutrophil and monocyte chemotaxis)
  • Complement proteins and complement regulatory proteins
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13
Q

Describe cytokines

A

These are the small polypeptides released by a cell in order to change the function of the same or another cell
- these chemical messengers are found in many organs (especially the immune system)

The main immune cytokines:

  • Interfererons (IFN)
  • Interleukins (IL)
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14
Q

Describe chemokines

A

The defining feature of Chemokines

  • is their function as chemotactic molecules
  • i.e. they attract cells along a gradient of low to high chemical concentration, from the blood into tissues (and into lymphatics)

They also have the ability to activate immune cells

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15
Q

What does Interleukin-6 (IL-6) do?

A

Acts on the liver

  • Production of acute-phase proteins (C-reactive proteins)
  • elevated temperature
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16
Q

What does IL-8, a chemokine, do?

A
  • Activation of the vascular endothelium

- Attraction/activation of neutrophils

17
Q

What is Complement, or the complement system?

A

Complement

  • an assortment of macromolecules circulating in the blood
  • precipitates in a specific sequence and forms a Membrane Attack Complex on cell membranes of pathogens that enter the bloodstream

They act as opsonins

Neutrophils and macrophages

  • possess C3b receptors
  • that induce these cells to phagocytose microorganisms bearing C3b on their surface
18
Q

Describe how complement proteins can act as chemotaxants?

A

Complement also attract immune cells to the site of infection and lead to the destruction of microbes

19
Q

Describe the basic mode of action of complement and phagocytes function

A

A complement fragment binds to a microbe

This complement then facilitates the interaction with a complement receptor - C3b (which exists on a Phagocyte)

The receptor-complement complex is internalised into the cell
- by phagocytosis

Now contained within a vacuole, the ingested microbe may now be destroyed

20
Q

Describe the main functions of complement activation:

A
  • promote inflammation (through C3a, C4a, C5a)
  • recruit cells (chemotaxis)
  • kill targeted cells - MAC
  • solubilise and remove from circulation the antigen-antibody complexes

(this protects unaffected tissues from these large, insoluble composites - could result in unwanted inflammation)

21
Q

What are the 3 types of blood cells?

A
  • Erythrocytes (RBCs)
  • Thrombocytes (platelets)
  • Leucocytes (WBCs)
22
Q

Describe Leukocytes/WBCs

and state how they leave capillaries

A

Leukocytes (WBCs)

  • involved in immune response (acquired)
  • when they arrive at their destination
  • they leave the capillaries via diapedesis (migration between endothelial cells), and enter the CT compartment, and do function

2 major categories:

  • Granulocytes
  • Agranulocytes
23
Q

Describe the 2 types of WBCs

A

Agranulocytes: leukocytes that do not possess specific granules

  • Lymphocytes
  • Monocytes

Granulocytes: leukocytes that possess specific granules

  • Neutrophils
  • Eosinophils
  • Basophils
24
Q

Describe neutrophils

A

Neutrophils
- polymorphonuclear leukocytes - granulocyte
- 60-70% of WBC count
- nucleus has 3 lobes
- cell membrane of neutrophils display Fc receptor and complement receptor for C3b
> and L-selectins and integrins that facilitate adhesion to the endothelial lining in preparation for diapedesis

Neutrophils release enzymes from specific granules
- to kill bacteria
Neutrophils phagocytose bacteria
- using membrane-bound Fc and C3b receptors

Neutrophils accumulate in large quantities at sites of bacterial infection and tissue injury
- possess prominent phagocytic capabilities

25
Q

Describe lymphocytes

A

Lymphocytes

  • round cells with an acentric nucleus that occupies most of the cytoplasm
  • form 20-25% of WBCs

They are agranulocytes
- BUT they have some azurophilic granules (are lysosomes)

B cells make up 15% of all lymphocytes

  • responsible for the humorally mediated immune response
  • when antigenically stimulated, they become anti-body producing plasma cells

T cells form 80% of all lymphocytes
- responsible for cell-mediated immune response

Null cells compose 5% of the lymphocyte population

  • stem cells
  • Natural killer cells
26
Q

Describe monocytes

A

Monocytes

  • round cells with a kidney-shaped nucleus - largest blood cell in circulation
  • once they are released from bone marrow (a few days later), they leave the bloodstream, enter the CT compartment, and differentiate into macrophages

Monocytes:

  • preferentially phagocytose dead and disrupted cells and invading pathogens
  • they are highly Phagocytic for microbes and particles (which have been marked for clearance by Ig and/or Complement)

They release signalling molecules

  • cytokines and chemokines
  • that induce inflammatory responses and proliferation of other immune cells

They are found:

  • to be persisting for long periods at sites of chronic inflammation and infection
  • also prominent in granulomatous processes
27
Q

Describe what happens when a Monocyte is activated:

A

Once activated

  • they engulf and kill microorganisms
  • in doing so, they release a range of pro-inflammatory cytokines (IFN-y, IL-6, IL-2, and TNF)
  • and have the capacity to present fragments of the microorganism to T cells (antigen presentation)
28
Q

Describe the antigen presentation stage of Monocytes, following activation and phagocytosis

A

Monocytes

  • become antigen-presenting cells that phagocytose antigens
  • and break them down into smaller antigenic units - epitopes
  • then place them on their membrane-bound MHC-II
  • and present these protein fragments to other immune cells (lymphocytes)
29
Q

Describe Dendritic Cells

A

The major function of Dendritic Cells:

  • is the activation of naive T-cells
  • to initiate adaptive immune responses

Dendritic cells have:

  • dendritic morphology
  • the ability to process and pressent antigens to CD4+ and CD8+ T-cells, couples with the ability to activate these T cells from a naive state
  • the ability to dictate the T-cells future function and differentiation
30
Q

Describe the Clusters of Differentiation classification (CD)

A

Immune cells are distinguished by the surface receptors and proteins that they express
- in order to mediate their particular range of immunological functions

Their surfaces are covered with these proteins which can be used to indicate the cell lineage or differentiation pathway.

Surface molecules defining the origin and function of selected groups of cells

  • known as CLUSTERS OF DIFFERENTIATION (CD)
  • over 300 CD numbers exist

e.g. CD4 count - peripheral blood lymphocytes

31
Q

Describe the lymphoid system

A

System that:

  • removes fluid from limbs and rest of body (to avoid selling)
  • allows WBC to travel all over the body
  • system has valves to prevent backflow and stasis - (and fluid is moved by muscular contraction and pulsing of adjacent blood vessels) - leads back to the venous system
32
Q

Describe lymph nodes

A

Lymph nodes are

  • widenings in the lymphoid system
  • though nodes in disease can enlarge
  • secondary lymphoid organs
33
Q

Outline the stages of primary and secondary immune responses (briefly)

A

Primary and secondary adaptive immune responses

On initial antigen encounter,
- both humoral and cell-mediated adaptive responses are limited in intensity and duration (primary response)

Subsequent exposures to antigen (secondary response)

  • are characterised by increased intensity and duration
  • each epitope elicits a separate response

Medicine 1 - 10 Blood and Immunity (6 decks)

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