Micro Unit 13

AIDS (Acquired Immunodeficiency Syndrome)

• caused by Human Immunodeficiency Virus (HIV)

  • HIV is a retrovirus and uses reverse transcriptase to copy its viral RNA to viral DNA

• transmitted by sexual contact or contact with infected body fluids

• HIV-1 is seen throughout the world

• HIV-2 is mostly seen in Africa

HIV uses what for attachment

two glycoproteins

• they bind receptors on helper T cells, dendritic cells, and macrophages

Other STIs contribute to HIV infection because

they damage genital tissue

Leading method of transmission for HIV

sexual activity

2nd most common form of transmission for HIV

IV drug abuse

Prime target for initial infection of HIV

cells of the mucosal immune system

• dendritic cells bind to the HIV-1 envelope proteins with high affinity

• hold the virus until susceptible T cells come along and are infected

HIV infection has 3 phases

1. Acute phase

2. asymptomatic phase

3. symptomatic phase

3 phases of HIV infection: Acute Phase

• occurs in the first few days after infection

• virus is produced in large quantities by infected lymphocytes

  • results in lymphadenopathy (swollen lymph nodes)

• Viremia is greatly reduced by 10 weeks after initial infection

3 phases of HIV infection: Asymptomatic Phase

begins 3-4 months after the initial infection

• viremia is very low

• HIV is latent in memory T cells and macrophages

• a protracted phase-can last for years (clinical latency)

3 phases of HIV infection: Symptomatic Phase

end stage of infection

• infected individuals develop clinical symptoms

• viral replication increases in the lymph nodes

  • architecture of the lymph nodes deteriorates

Clinical symptoms of HIV

• increased susceptibility to opportunistic infection

• generalized lymphadenopathy

• appearance of lesions

• some patients develop cancers

Response to HIV Infection

-Without treatment, 10% of HIV infections progress to AIDS for the first 3 years

-More than 80% show signs of clinical disease within 10 years

HIV replicated best in

activated T cells

Antibody Response to HIV

IgG is the dominant form of antibody in any HIV infection and is involved in:

• neutralizing the virus

• blocking viral receptors

• promoting complement-mediated reactions

Cellular Response in HIV

all infected individuals have a ceullar adaptive response to AIDS

• cytotoxic T cells are programmed to recognize all HIV-1 proteins

Staphylococcal enterotoxins cause production of

cytokines that suppress the immune system

How does Neisseria gonorrhoeae affect dendritic cells

induces dendritic cells to display proteins on their surface with immunosuppressive properties

In primary immunodeficiency disease, the immune system

does not function properly because of a genetic defect in the host

Recurrent infections by pyrogenic bacteria indicate:

• defects in antibody production

• defects in the complement system

  • defects in phagocytosis

Inherited immunodeficiency diseases are caused by

recessive gene defects

The immune system can fail by

reacting against self components in the body

Autoimmune diseases vary in 3 ways

severity, effector mechanisms, and the tissue affected

Autoimmune diseases are divided into 2 types

1. Organ or tissue specific : reaction against self is confined to certain organs

   • Type 1 insulin-dependent diabetes - attacks insulin-producing cells in the pancreas

   • Rheumatoid arthritis - attacks the joints

   • Multiple sclerosis - attacks nervous tissue

2. Systemic autoimmunity: affects multiple organs and has body wide effects

   • systemic lupus erythematosus - produces antichromatin antibodies that affect many organs

Pathogens can disrput regulation of the immune response by:

• preventing apoptosis

• secreting their own cytokines

Autoimmunity results in chronic disease because:

• it is impossible to rid the host of the self antigen

• the autoimmune response destroys host tissues

  • tissue destruction frees up more self-antigens

  • this causes production of more autoantibodies

  • which destroys more tissue

An allergic reaction is a form of

immune response

What happens after exposure to an allergen:

• mast cells induce inflammatory reaction including:

  • synthesis of prostaglandins, leukotrienes, cytokines

• Allergens cross-link with an IgE bound to a receptor on a mast cell

Inflammatory mediators are released causing:

• increases in local blood flow (vessel permeability)

• production of enzymes and tissue destruction

• smooth muscle contraction

• increased secretion of mucus

• influx and activation of leukocytes

Eosinophils have 2 functions in allergic reactions:

1. Release highly toxic granules and free radicals

   • kill microorganisms

   • cause significant tissue damage in allergic reactions

2. Produce chemical mediators, prostaglandins, leukotrienes, and cytokines

   • enhances and amplifies the allergic reaction

eosinophils are strictly regulated (T or F)

True

Allergic reactions are divided into immediate and late-phase

1. Immediate phase reactions

   • ex. IgE-mediated mast cell activation

2. Late-phase reactions

   • due to elaboration of mediators

     • leukotrienes, chemokines, and cytokines

Clinical effects vary according to the site of mast cell activation

This depends on 3 variables:

1. Amount of allergen-specific IgE present

2. Route by which the allergen is introduced into body

3. How much allergen enters the body

Allergen can be deposited into the blood or rapidly absorbed causing

systemic anaphylaxis; aka anaphylactic shock

Allergic rhinits

• intense itching

• sneezing

• localized edema and blocked nasal passages

• nasal discharge

Allergic conjunctivitis occurs when

allergens enter the eye

Allergic asthma is serious and can be life threatening

• immediate bronchial constriction

• increased production of fluids and mucus

• makes breathing difficult