Overview of the Immune System

Efren N. Aquino M.D.

The Formed ElementsThe Formed Elements

• Produced in red bone marrow• Hematopoietic (blood-forming) Hematopoietic (blood-forming)

stem cellsstem cells can develop into any blood cell

• Stem cells are short-lived tissue cells

Lymphoid tissue is primarily localized in the lymph nodes of the lymphatic system and is also in the spleen, thymus, and bone marrow.

Several classes of white cells are produced, including the lymphocytes, monocytes and macrophages.

How Do Infections Occur?How Do Infections Occur?

Factors involved in infection1. Portal of entry2. Virulence of organism

• Aggressiveness• Toxin production

3. Dose (number) of pathogens4. Individual condition

(predisposition) to infection

The Immune SystemThe Immune System

Types of general body defenses against disease

• Nonspecific defenses• Effective against any harmful

agent• Specific defenses

• Effective against a certain agent only

Body Defenses: Body Defenses: • Successive lines of defense

Simple outer barriersMore complicated responsesImmunity (ultimate defense

mechanism)

Nonspecific Defenses1. Chemical and mechanical barriers2. Phagocytosis3. Natural killer cells4. Inflammation5. Fever6. Interferon

Chemical and Mechanical Barriers

Skin Mucous

membranesCilia

Body secretionsTearsPerspirationSalivaDigestive juices

ReflexesSneezingCoughingVomitingDiarrhea

Phagocytosis

White blood cells take in and destroy waste and foreign material

• Neutrophils• Macrophages

Natural Killer CellsType of lymphocyte• Can recognize body cells with

abnormal membranes• Found in lymph nodes, spleen, bone

marrow, blood• Secrete protein that breaks down cell

membrane

InflammationInfection is inflammation caused by

pathogens• Inflammatory reaction

• Heat, redness, swelling, pain• Leukocytes enter tissue• Pus is produced• Lymph nodes enlarge

The classic signs and symptoms of acute inflammation: English

RednessHeatSwellingPainLoss of function

LatinRuborCalorTumorDolorFunctio laesa

FeverAs phagocytes work, they release

substances that raise body temperature• Stimulates phagocytes• Increases metabolism• Decreases some organisms’ ability to

multiply

Interferon• Group of substances that prevent

nearby cells from producing more virus• IFN a (alpha)• IFN b (beta)• IFN g (gamma)

• Also acts nonspecifically on immune system cells

Specific Defenses:Specific Defenses:ImmunityImmunityPower to overcome a specific disease agent• Inborn immunity

• Inherited in genes• Acquired immunity

• Develops after birth• Acquired naturally or artificially• Active or passive

Types of immunity.

Inborn Immunity

Differences in physical constitution• Species immunity• Individual immunity

Acquired Immunity

Develops in a person• During lifetime• From encounters with specific

harmful agents

What is the difference between inborn and acquired immunity?

Antigens

Foreign substances that • Enter body • Induce immune response of certain

lymphocytes• T cells• B cells

T CellsOriginate in stem cells in bone marrow• Change to T cells in thymus• Become sensitized to specific antigens• Produce cell-mediated immunity

• Cytoxic T cells• Helper T cells - interleukins• Inhibitory/Regulatory T cells • Memory T cells

• Macrophages

Activation

of T-cells

Memory T-cells

1. Cytoxic T cells - destroy2. Helper T cells - interleukins3. Regulatory T cells - inhibit4. Memory T cells – don’t engage

Cluster of Differentiation 4 : CD4 - a glycoprotein that is found primarily on the surface of helper T cells; "CD4 is a receptor for HIV in humans"

B Cells and AntibodiesAntibody (Ab) also known as

immunoglobulin (Ig) is a substance produced in response to antigen

• Manufactured by B cells (B lymphocytes)• Must mature in fetal liver or in lymphoid

tissue• Provides humoral immunity• Contained in gamma globulin fraction of

blood plasma

Activation of B cells. The B cell combines with a specific antigen. The cell divides to form plasma cells, which produce antibodies. Some of the cells develop into memory cells, which protect against reinfection.  

What two types of cells develop from activated B cells?

What is an antibody?

What type of cells produce antibodies?

The Antigen–Antibody Reaction

ComplementComplement is the enzymatic activity of a group of nonspecific proteins in blood:

• Coats foreign cells• Destroys cells• Promotes inflammation• Attracts phagocytes

Naturally Acquired Immunity

Immunity acquired through contact with a specific disease organism

• Active immunity• Passive immunity

What is the difference between the active and passive forms of naturally acquired immunity?

Artificially Acquired Immunity

Vaccination (immunization) can cause a person’s immune system to manufacture antibodies

• Preventive measure• Risk of side effects

Types of Vaccines

• Live• Attenuated• Toxoid• Killed by heat or chemicals• Antigenic component• Genetically engineered

Boosters

• Active immunity does not always last a lifetime

• Repeated inoculations (booster shots) help maintain high titer of antibodies in the blood

• Number and timing varies with vaccines

Passive Immunization

Acquired by administration of immune serum (antiserum)

• Short-lived immunity• Used in emergencies• Often derived from animals• May cause sensitivity reaction

What is an immune serum and when are immune sera used?

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