Lecture 12 - Internal Host Defence

8/13/2019 Lecture 12 - Internal Host Defence

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Internal Host Defence

Dr. Linroy Christian


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Non-specific Immune Response

Phagocytic cells Neutrophils

Monocytes

Macrophages

Eosinophils

Attracted to the site of infection by:

Damaged tissue

Products from bacterial cells

Antibodies

Complement proteins


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Complement A complex pathway of proteins that enablemicrobes and other antigens to be destroyed

Some complement proteins coat microbes

causing them to be recognised by phagocytes Other complement proteins actively lyse cells

Some trigger the release of histamine frommast cells

Antibody plus complement render someinvading microbes susceptible tophagocytosis that would otherwise evade thisprocess


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Non-specific Immune Response Interferon

Proteins that prevent viral replication

All cells produce type I (alpha- and beta-

interferon) when invaded by a virus

Interferon disrupt viral replication by inducingthe production of enzymes that degrade

mRNA

T cells and NK cells produce type II (gamma-

interferon)

Gamma-interferon stimulates macrophages

and NK cells and has an effect on antibody

production


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Natural Killer Cells (NK Cells)

Lymphocytes

Monitor the body for parasites and malignant

cells

Release enzymes that destroy cells


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Specific Immune Response

Two types of cells make up the specificresponse, the B cells and the T cells

Two types of specific responses:

Humoral (antibody response) Cell-mediated response

The cell-mediated response or cellular

immunity involves the direct action ofimmune cells. Antibody production or

activity is limited in this type of response


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Humoral Immune Response

Immunoglobulins (antibodies) are Y-shaped proteins that are able to combine

with antigens

There are 5 major classes ofimmunoglobulins:

IgG, IgA, IgM, IgD and IgE

IgG is the most common in humans


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Humoral Immune Response The antigen on the surface of microbes is recognised by

receptors on the surface of B lymphocytes Plasma Cells (B cells activated by an antigen) secrete

specific antibodies

When antibodies bind to antigen, the first protein in the

complement series is activated Complement protein binds to specific site on antibody

The invading cell covered with antibodies andcomplement is destroyed by phagocytes

IgE present on mediator cells initiate secretion ofhistamine from these cells when an allergen isencountered

B cells also have receptors for proteins from Tlymphocytes, which influence their activity


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Humoral Immune Response


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Cell-Mediated Response

Initiated by T cells T cell receptors recognise specific foreign

protein on the surface of the infected cell

or immune cell that has engulfed apathogen

Cytotoxic T cells destroy infected and also

dysfunctional cells (tumors) T helper cells stimulate B cells as well as

phagocytes


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Cell-Mediated Response


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Self Recognition

Major Histocompatibility (MHC) marker

T cells that recognise self cells are

destroyed during their development

MHC markers vary between individuals

MHC typing is important in grafts

Autoimmune diseases occur when selfrecognition is defective


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Autoimmune Diseases

Rheumatoid Arthritis

Affects joint tissue

Multiple Sclerosis

Affects the Central Nervous System

Lupus

Can affect all cells of the body


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Inflammatory Response

Can be brought on by:

Release of prostaglandins due to injury or

infection

Release of histamine by immune cells


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Immunisation Confers specific immunity to disease

This may be done in one of two ways

Administering antigen (active immunity) Immunity develops over a period of weeks

Administering antiserum (passive immunity) Immunity develops immediately

IgG from placenta, IgA from breast milk

A vaccine is an antigen or mixture ofantigens that confers specific immunity

There are several types of vaccinesavailable


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Vaccine Types Killed organisms

Whole organisms may be killed by heat or chemical treatment

Typhoid and whooping cough vaccines

Live attenuated strains

Can infect and multiply but are avirulent

Induce a greater immune response than killed organisms

May revert to virulent state in some cases Polio, Measles, Mumps, Rubella, BCG vaccines

Purified components

Toxoids (modified toxins) can be used

Not as strong an antigen as the original toxin

Diphtheria and Tetanus vaccines

Genetic recombination

The antigen of one organism may be produced in anotherorganism

Hepatitis vaccine

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Lecture 12 - Internal Host Defence