Download Immunological Disorders There are three types of immunological

Immunological Disorders
There are three types of immunological disorders:
1. Hypersensitivity (allergic reactions) 2. Autoimmune disease 3. Immunodeficiency
Most Hypersensitivity (allergic reactions) fall into one of four major
types:
1. Type I: Immediate IgE-mediated
2. Type II: Cytotoxic
3. Type III: Immune complex-mediated
4. Type IV: Delayed cell-mediated
Type I Hypersensitivity
1. Also called IgE Mediated Hypersensitivity
2. First exposure to antigen induces an IgE antibody response leading to
sensitization
3. Antigen is taken up by dendritic cells (APC) and merged with MHC
molecules
4. APC presents the antigen to T-cells
5. Activated T-cells release cytokines that stimulate B-cells to produce
plasma cells which secrete large amounts of IgE
6. IgE antibodies bind to mast cell receptors and the individual is now
“sensitized”
7. During the subsequent exposures, antigens activate IgE antibodies on
the mast cell causing it to degranulate (A) Histamines, leukotrienes,
prostaglandins, and/or cytokines are released. (B) These chemicals are the
cause of hives, hay fever, asthma and anaphylactic shock.
Immunotherapy
1. Repeated injections of very small amounts of antigen are given over
several months
2. This regimen leads to the formation of specific IgG antibodies
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3. The IgG reacts with antigen before it can bind to IgE and therefore it
blocks the IgE reaction that might result in allergic reactions
Type II Hypersensitivity
1. Also called Cytotoxic Hypersensitivity because it utilizes antibodies
that can destroy normal cells by complement lysis or by antibodydependent cellular cytotoxicity (ADCC).
2. Generally occur within hours after exposure.
Transfusion Reactions :–
The ABO blood groups are the major cause of hemolytic anemia in blood
transfusion patients.
1. Recall that persons with A type blood possess the A antigen and the
natural antibody anti-B
2. Persons with B type blood possess the B antigen and the natural
antibody anti-A
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3. Persons with O type blood lack both the A and B antigens but possess
both the natural antibodies anti-A and anti-B
4. Persons with AB type blood possess both the A and B antigens but
possess no natural antibodies.
Hemolytic Disease of the Newborn :1. Also called Erythroblastosis fetalis
2. Results when mother is Rh- and baby is Rh+
3. Upon delivery, Rh+ antigens are transferred to the mother’s bloodstream which
causes her to produce anti-Rh antibodies.
4. If the mother becomes pregnant again with an Rh+ child, the antibodies cross the
placenta, enter the circulation of the fetus, and cause extensive fetal erythrocyte
damage
5. RhoGAM may be administered to prevent this reaction
A) Contains Rh antibodies and prevents the mother’s natural production of them
B) Widely used at 28 weeks and after delivery during all susceptible pregnancies.
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Type III Hypersensitivity
1. Also called Immune Complex-Mediated Hypersensitivity
2. Occurs within hours or days after exposure
3. When there is a slight excess of antigen, the antigen-antibody
complexes activate complements and stimulate neutrophil and basophil
degranulation
4. The complexes can also precipitate causing clots to form in the small
blood vessels leading to failure or death of the organ
5. Examples of Type III Hypersensitivity are:
1. Arthus reaction – localized tissue death
A) ex. Chronic Obstructive Pulmonary Disease (COPD)
2. Serum sickness – seen in individuals immunized/treated with animal
serum
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Type IV Hypersensitivity
1. Also called Delayed Cell-Mediated Hypersensitivity: occurs within
days after exposure
2. T-cells rather than antibodies are involved with this type
3. Example of delayed hypersensitivity is: Tuberculin skin test
Tuberculin skin test – a positive test results when circulating antibodies
(which are only present if the person has been exposed) bind to the
protein antigens of the tuberculosis bacteria introduced under the skin
- The redness results mainly from sensitized T-cell reactions, the release
of cytokines and the influx of macrophages to the injection site
- False positive tests can result from exposure to another species of
Mycobacterium or use of the BCG vaccine
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Autoimmune Diseases
- Autoimmune diseases occur when the immune system of the body
responds to its own tissues as if they were foreign
- May result from normal reactions to antigens that are similar, though
not identical, to the host’s normal antigens
- Autoimmune reactions occur over a spectrum ranging from organspecific to widespread response not limited to any one tissue
1. Grave’s disease (thyroid) and Insulin-dependent diabetes mellitus
(pancreas) are organ specific
2. Lupus and rheumatoid arthritis are considered widespread
- Treatment of Autoimmune diseases
1. Usually treated with immunosuppressive drugs that kill dividing Tcells and thus control the response
2. Steroids and other anti-inflammatory drugs are often used to relieve
symptoms
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Infection: pathogenic microorganisms penetrate the host defenses, enter
the tissues, and multiply.
Disease: The pathologic state that results when something damages or
disrupts tissues and organs.
Infectious disease:
the disruption of a tissue or organ caused by
microbes or their products.
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Pathogenicity: an organism’s potential to cause infection or disease
– True pathogens
– Opportunistic pathogens
Virulence factor: any characteristic or structure of the microbe that
contributes to its virulence
Infectious Agents that Enter the Skin
• Examples
– Staphylococcus aureus
– Streptococcus pyogenesHaemophilus aegyptius
– Chalmydia trachomatis
The Gastrointestinal Tract as Portal
• Examples
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– Salmonella,
Shigella,
Vibrio,
Certain
strains
of
Escherichia coli, Poliovirus, Hepatitis A virus, Echovirus,
Rotavirus, Entamoeba hitolytica, Giardia lamblia
The Respiratory Portal of Entry
• Examples
– Streptococcal
sore
throat,
Meningitis,
Diphtheria,
Whooping cough, Influenza, Measles, Mumps, Rubella,
Chickenpox, Common cold, Bacteria and fungi causing
pneumonia
Urogenital Portals of Entry
• Examples
– Syphilis
– Gonorrhea
– Genital warts
– Chlamydia
– Herpes
Pathogens that Infect During Pregnancy and Birth
• Some microbes can cross the placenta (ex. the syphilis
spirochete)
• Other infections occur perinatally when the child is
contaminated by the birth canal
– TORCH
(toxoplasmosis,
other
cytomegalovirus, and herpes simplex)
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diseases,
rubella,
Bacterial Toxins
• Specific chemical product that is poisonous to other organisms
• Toxigenicity: the power to produce toxins
• Toxinoses: a variety of diseases caused by toxigenicity
• Toxemias: toxinoses in which the toxin is spread by the blood
from the site of infection (tetanus and diphtheria)
• Intoxications:
toxinoses caused by ingestion of toxins
(botulism)
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Signs and Symptoms of Inflammation
• Fever, pain, soreness, swelling
• Edema
• Granulomas and abscesses
• Lymphadenitis
• Lesion: the site of infection or disease
Signs of Infection in the Blood
• Changes in the number of circulating white blood cells
• Leukocytosis
• Leukopenia
• Septicemia:
general state in which microorganisms are
multiplying in the blood and are present in large numbers
• Bacteremia or viremia: microbes are present in the blood but are
not necessarily multiplying
Transmission
• Contact transmission
• Indirect transmission
– Vehicle: any inanimate material commonly used by humans
that can transmit infectious agents (food, water, biological
products, fomites)
– Contaminated objects (doorknobs, telephones, etc.)
• Food poisoning
• Oral-fecal route
– Air as a vehicle
• Indoor air
• Droplet nuclei
• Aerosols
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Nosocomial Infections: The Hospital as a Source of Disease
• Nosocomial infections: infectious diseases that are acquired or
develop during a hospital stay
• 2-4 million cases a year
• The importance of medical asepsis
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Koch’s Postulates
• Find evidence of a particular microbe in every case of a disease
• Isolate that microbe from an infected subject and cultivate it in
pure culture in the laboratory
• Inoculate a susceptible healthy subject with the laboratory isolate
and observe the same resultant disease
• Re-isolate the agent from this subject
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