Download Quick overview of immune system

Quick overview of immune system
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• Immune system: acquired immunity
– After exposure to a foreign substance, your body is
able to rapidly react against it next time.
• Immune system is a complex interplay between
cell signals (cytokines such a interleukins) and
different cell types.
• Although macrophages are involved, the
immune system features T cells and B cells,
types of lymphocytes.
Nature of antigens
• The immune system recognizes, responds to,
and remembers molecules that are antigens.
• An antigen:
– Is foreign
– Is large
– Is molecularly complex.
• Proteins and polysaccharides on the surface of
bacteria are antigens, as are viral proteins on
the surface of your infected cells.
– Also, molecules on pollen and animal skin flakes:
allergies are an immune response as well.
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Dual Nature of the immune system
• Humoral and cell mediated
– Humoral refers to body fluids, specifically that this
branch of the immune system uses antibodies
which are protein molecules dissolved in blood,
body fluids, and secretions.
• B lymphocytes are the source of antibodies
– Cell mediated refers to the direct involvement of
cells to attack an infection
• T lymphocytes either kill cells directly or recruit
macrophages to kill cells directly
Basic Antibody structure
•Classic lock
& key like an
enzyme; sites
bind
specifically to
antigens.
Antibodies attach to antigens,
cover up binding sites, and
preventing the action of the
molecules, agglutinating,
precipitating, and neutralizing.
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Pathogenic Viruses
• Name of virus; what family it belongs to; what
disease it causes.
– DNA or RNA? Ss or ds?
– Characteristics of disease, symptoms.
– Viral virulence factors
• Epidemiology: reservoirs, vectors
• Immunizations
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Brief review
• Non-cellular “life forms”
– Consists of nucleic acid and capsid (protein)
– Some types possess envelope, spikes, accessory
proteins
• Obligate intracellular parasites
– Nucleic acid enters host cell, directs operations
– Ultimately, new copies of viral N.A., proteins made
• Virus depends mostly on host cell machinery
– Following assembly, new virions escape to infect
new hosts
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Attack and defense
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• Virus has ways of attacking
– Specific binding to host cell receptor
• Receptors involved in normal cell functions
– Virus may regulate cell division for its own
replication
– Insertion of viral DNA into chromosome allows virus
to hide from immune system
Defense by host
• Host has ways of defending
– Cell mediated immunity (T cells): infected cells
killed.
– Antibodies intercept virions between cells, in fluids
– Interferon produces anti-viral state, prevents
replication
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Our selections for Sp 2005
• Herpes Virus family
– HSV 1 & 2; VZV; and CMV
• Hepatitis viruses
– Hep A, B, and C: all unrelated, and transmitted
differently, but cause similar disease.
• Mosquito-borne viruses of Arkansas
• Influenza
• HIV (info repeating or supplementing guest
speaker Debbie Biazo)
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Herpes virus family
• Human herpes viruses now numbered
– But common names easier to use.
• As a family:
– ability to become latent;
– predilection for either nervous tissue or lymphocytes;
– ability to cause cancer.
• Herpes roster:
– Herpes simplex, Varicella zoster, cytomegalovirus,
Epstein Barr, roseola, Kaposi’s sarcoma virus.
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Herpes Simplex viruses
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• HHV1 (above the waist)
– Typically oral, cold sores; flu-like symptoms, etc.
• HHV2 (genital), STD and neonatal
– Painful, contagious sores on genitals, overlap w/ HHV1.
• Latency
– Viruses enter nearby nerve cells, remain until activated
by stress of some sort, cause disease, then return.
• Spread and treatment:
– Person to person by direct contact; spread within
host by forming syncytia, escape immune system.
– Acyclovir helps; no cure, lifetime infection.
Herpes family: Varicella Zoster
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• Varicella: chicken pox; Zoster: shingles
– Chickenpox (not a pox virus), respiratory, disease
becomes systemic with fever, malaise, skin lesions.
– Very contagious; usually mild, esp. in children
– Virus can become latent in nerves like Herpes
simplex
• Recurrence: shingles; rash, pain, on one side
• Acyclovir can lessen symptoms
– Beware of salicylates + viruses: Reyes syndrome
– Vaccination: Varivax: attenuated vaccine
Herpes family: Cytomegalovirus
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• CMV (HHV5): Infection results in enlarged cells
– Widespread asymptomatic infections, latency
– Virus shed in body fluids: sex, birth, transplants
– Problem for unborn, immunosuppressed, transplant
patients; major cause of viral-induced birth defects.
Hepatitis
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• Hepatitis is inflammation of the liver
– Liver especially important in metabolism
• Breakdown of drugs, toxins, waste products
– Damage results in accumulation of bilirubin
• Bilirubin is stage in hemoglobin breakdown
• Results in yellow color: jaundice
– Hepatitis can be caused by several different viruses
• Hepatitis A, B, and C viruses all cause liver
damage, but are unrelated viruses.
Hepatitis B
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• A DNA virus: “Hepadnavirus”
• Hepatitis B released from live cells, so
accumulates in high numbers in body fluids.
– Blood of infected person is rather infectious
– Cuts, piercing, sex, childbirth, etc.
– Large amounts of empty capsids ties up antibodies.
• After exposure, long incubation, long disease
– 10% have chronic infections
– The younger the host, the likelier chronic infection
Hep B continued
• Chronic infection correlated with liver
destruction
– Liver tissue replaced by scar tissue; liver failure
– Long term exposure to virus increases risk of liver
cancer
• Insertion of HBV DNA into chromosome may
activate oncogenes
• Vaccination now recommended
– Because of bad result of early infection and great
danger of liver damage, liver cancer.
– Recombinant vaccine.
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Hepatitis A virus
• A small RNA virus, “Picornavirus”
– Transmitted by fecal-oral route
– Incubation for 1 month, followed by fever, nausea,
anorexia, jaundice
• T cells attack infected liver cells
– No chronic infections, patients recover.
• Note comparisons to Hepatitis B:
– RNA vs DNA
– Shorter disease, few long term problems
– Mode of spread completely different
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Hepatitis C
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• Another RNA virus, different group: “Flavivirus”
– Causes chronic infections
• Can be mild, or destructive
• Long term infections increase risk of cancer.
– Transmission like Hep B: blood, sex, transplants
Arkansas Arboviruses
• Not an official taxonomic group, but short for
“arthropod-borne”
– Includes Flaviviruses, Togaviruses, and others.
– Zoonotic, spread from animals to people by
arthropod vectors, especially mosquitoes.
• Reservoirs may be birds, various mammals
– Result in two main types of illnesses
• Encephalitis, inflammation of the brain
• Hemorrhagic fever: high fever with bleeding
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Arkansas Arboviruses
• Encephalitis: spread by skeeters
– In Arkansas: Eastern Equine;
• Togavirus;
• Also infects, kills horses. Most dangerous.
– St. Louis encephalitis,
• Flaviviral diseases; Human disease.
• Usually not serious.
– West Nile virus
• Flavivirus; imported to US, spread from NYC
• Disease mostly in young and elderly
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Orthomyxovirus
• Influenza: a serious respiratory disease
– Virus has a segmented genome
• 8 different RNA molecules
– Spikes: Hemagglutinin (for infecting cells) and
neuraminidase (for escaping them)
– Antigenic drift and shift
• Drift: small mutations, making host susceptible
• Shift: major mixing of RNAs, whole new virus.
– Attack on respiratory tract
• Kills ciliated epithelial cells, allows bacterial
infections. Release of interferon causes
symptoms.
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influenza
• Changes in H and N (antigenic shift)
– Mixing of viruses that infect birds, pigs, produce
new strains able to jump to humans.
– New antigenic type leaves population unprotected
– Numerous epidemics throughout history
• Flu of 1918-1919 killed 20 million
– Asia watched very carefully
– Flu vaccines made from deactivated viruses
• Slow process, so every year correct strains are
“guessed”.
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HIV/AIDS
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• Infection
– 4 main types of cells infected, esp. T helper cells
• Have CD4 glycoprotein on surface
– After RNA is copied into cDNA, cDNA inserts
• Infection is for life
– Chronic infection
• T cells continually made, continually destroyed
• Eventually, host loses
– AIDS diagnosis:
• CD4 count below 200/µl; opportunistic infections
Treatment and prevention
• Prevention is easy
– Practice monogamous sex, avoid shared needles
– HIV cannot be spread by casual contact, skeeters
– Fastest growing victim demographic is YOU.
• Not just a “gay disease”
• Treatment is expensive, but usually works
– Nuceloside analogs, protease inhibitors
• Processing viral proteins requires protease
– About $1500 a month for drugs
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