Immunity

Introduction to specific immunity

Introduction to ImmunityImmunity is a physiological reaction of the body to

factors it considers threatening and foreign to it

Immune system can distinguish ‘self’ from ‘non-self’

A factor which evokes the immune response is referred to as an Antigen (or immunogen)

Antigens may be isolated molecules or may be molecules at the surface of an invading cell

Antigens are usually exogenous, but may be endogenous (i.e. part of the auto immune reaction)

Non Specific or Specific Immunity?

Non-specific = Innate = Inherited defence mechanisms

Specific = Acquired = Prior exposure

Non-specific Immunity Eyes, Mouth, NoseLungs, Skin, StomachReproductive SystemLarge intestine, Urinary Tract

Non-Specific Immunity

Eyes e.g. Lysozyme in tear fluid, flushing action

Mouth e.g. Lysozyme in saliva, flushing action

Nose e.g. sneezing, nose hairs

Non-Specific ImmunityLungs

e.g. coughing, muco-ciliary clearance

Skine.g. waterproof skin/physical barrier, sebum and acid pH

Non-Specific ImmunityStomach

e.g. HCl in gastric juice

Reproductive Systeme.g. competition from harmless bacteria in vagina, acid pH of vagina, antibacterial proteins in semen

Non-Specific ImmunityLarge intestine

e.g. competition from normal gut flora

Urinary Tracte.g. directional flow and flushing action of urine

Non Specific Responses: Phagocytosis and Inflammation

Phagocytosis

Phagocytes contain lysosomes with enzymes

Phagocytes adhere to, engulf and destroy (digest and recycle) micro-organisms

Phagocytosis

Phagocytic cells include

• Neutrophils

• Macrophages

• Monocytes

Phagocytosis

Neutrophils

Generated in bone marrow

Comprise 50-70% of total white cell count

Recognise and phagocytose unwanted or foreign materials, then die

Phagocytosis

Macrophages

Highly mobile cells that migrate through connective tissue

Widely distributed throughout body tissues

Role is to phagocytose large bacteria and dead body cells

Phagocytosis

Monocytes

Multiple roles in immune function:• Replenish resident macrophages • In response to inflammation signals, can move

quickly to sites of infection in the tissues and differentiate into macrophages

• Have large kidney shaped nucleus

[Recognition by phagocytes can be enhanced by the binding of antibodies to the bacteria]

PhagocytosisPhagocytes are attracted to the micro-organism by a

process known as Chemotaxis

Neutrophils and monocytes

are able to squeeze through

tiny gaps between adjacent

endothelial cells

(Diapedesis)

PhagocytosisWhat intracellular structures (necessary for digesting ingested

particles) are highlighted in the diagram ?

What happens to the bacterium?

InflammationMast cells release histamine

Histamine:

• Increases blood flow via vasodilatation

• Increases capillary permeability

Both processes result in more phagocytes to the area

Inflammation and Phagocytosis

Identify (on the diagram below):• The site of bacterial entry? • What has coated the bacterium? • Where have the antibodies come from? • Where is the phagocytic cell coming from? • What has activated the mast cells? • What chemical has the mast cell released? • What effects has this chemical had on the

capillary?• What is diapedesis?

Diagram: Immune Response

Characteristics of Inflammation

• Redness

• Warmth

• Swelling

• Pain

• (+ or – Pus)

Leucocytes

Leucocytes are attracted

to an area of inflammation

by Chemotaxis

In which order do the

leucocytes arrive at the

area of inflammation?

Additional points

• What are endotoxins?

• What are Cytokines (and some examples)?

• What is the Complement system?

• What are Interferons?

Specific or Acquired Immunity

The immune system also produces very specific responses

Antigens / Immunogens induce specific immune responses.

Antigens include: foreign proteins, bacteria, viruses, foreign cells

Lymphocytes

Specific immunity involves Lymphocytes

Lymphocytes are derived from stem cells in the bone marrow

Lymphocytes replace themselves by cell division

T Lymphocytes

Lymphocytes that seed

the thymus become

T lymphocytes

(the thymus atrophies

after puberty)

T lymphocytes do

not secrete antibodies

Types of T Lymphocytes

Helper T cells* Activation of other defence cells (e.g. production of antibodies by B cells)* Regulate the response of both T Killer cells

and B cells

Suppressor T Cells* Inhibit T and B cell activities* Affect the amount of antibodies secreted

and moderate immune response (‘switch off’ immunity)

Types of Lymphocytes

Killer T cells

* Destroy specific cells with antigens on their surface

* Must be in actual contact with their victim cells

* Defend against viral and fungal infections

T Lymphocytes provide cell mediated immunity

B Lymphocytes

B lymphocytes are processed in the bone marrow

B lymphocytes combat bacterial infections as well as viral infections by secreting antibodies into the blood and lymph.

Antibodies bind to Antigens

B lymphocytes provide humoral immunity (blood and lymph are body fluids or humors)

B Lymphocytes

B Lymphocytes

B lymphocytes when stimulated produce:

a) Memory cells

b) Plasma cells

Antibodies

Antibody proteins are also known as immuno-globulins (or gamma-globulins)

[Immuno globulins may be found in, for example, colostrum]

Antibodies

lgG Main form of antibodies in circulation: production increased after immunization; secreted during secondary response

lgA Main antibody type in external secretions, such as saliva & mother’s milk

lgE Responsible for allergic symptoms in immediate hypersensitivity reactions

lgM Function as antigen receptors on lymphocyte surface prior to immunization; secreted during primary response

lgD Function as antigen receptors on lymphocyte surface prior to immunization; other functions unknown

B and T lymphocytes

Primary and Secondary Immune Response

On first exposure to a pathogen, the immune response is insufficient to combat the disease

There is a latent period in which there are insufficient amounts of specific antibodies

On second exposure to the same antigen antibody production is much more rapid

Immune Response

Application to practice• You might like to think about relevant cases from

practice (maintaining confidentiality, of course).

• You could also consider own history with regard to infections / vaccinations / problems with immunity (for example, when have you found yourself prone to infections?).

• For those with an interest in mental health, what is Agranulocytosis and what anti-psychotic drug has this listed as an adverse effect?

• What are the arguments for allowing children to be exposed to ‘childhood infections’?