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Detecting and
responding
DISEASE AND THE
IMMUNE RESPONSE
DISEASE
• What is disease?
• What is a non-infectious disease?
• examples
• What is an infectious disease?
• Examples
• Transmission – methods? –
(see homework)
• Incubation period
Detecting
• Humans, Animals, plants need a way of
detecting when they are “invaded” by
foreign cells or tissue so they can defend
themselves effectively.
• Immune system’s job
Pathogens
• Pathology – study of disease
• Pathogen – disease causing organism or non-cellular agent
• Main groups:• Viruses
• Bacteria
• Fungi
• Protozoans
• Prions
• Multicellular eukaryotic parasites
VIRUSES
• Non cellular infectious agents
• Can only be seen with an e.m.
• Completely parasitic (obligate intracellular
parasites)
• Host relationship is very specific –
glycoproteins on virus interact with
receptors on host cell membrane – e.g.
influenza virus and RBC’s
Size and shape of viruses
structure
Structure
Viral diseases
DNA viruses RNA viruses
Gastroenteritis Influenza
Respiratory tract infection Polio
Chicken pox Colds
Shingles Rubella
Warts AIDS
Measles
Mumps
diarrhoea
rabies
Transmission Electron Micrograph of an
Influenza A Virus
Transmission Electron Micrograph of HIV-1
Image provided by Dr. Edwin P. Ewing, Jr.Courtesy of the Centers for Disease Control and Prevention
Transmission Electron Micrograph of
Coronavirus
Image provided by Dr. Erskine Palmer.Courtesy of the Centers for Disease Control and PreventionNote the glycoproteins (arrows) on the viral envelope.
Transmission Electron Micrograph of
Poliomyelitis viruses
Image provided by J. J. Esposito and F. A. Murphy.
Courtesy of the Centers for Disease Control and Prevention.
Poliomyelitis viruses are naked viruses.
Polio - symptoms
Hosts
• Can infect all kinds of cells- human, plant,
animal, bacteria
• Many viruses spread by vectors – e.g.
mosquitos Ross River Virus
Reproduction
Treatment
• Antibiotics not effective
• Drugs which interfere with making of viral DNA or RNA might stop reproduction
• Vaccines most effective – inject or swallow inactivated virus into host – initiates the production of antibodies which help fight off the infection when it arrives.
• Rest – fast mutation of coat proteins on some viruses are a huge problem eg AIDS
PRIONS
• See p 137 AM
• PrPc proteins – normal and infectious
versions
• Discovered with Kuru in New Guinea
• E.g. CJD (Creutzfeld Jakob Disease)
• Bovine spongy encephalitis (Mad Cow
disease)
• No cure
Prions
Prions are implicated in BSE (Bovine Spongiform Encephalopathy or Mad Cow Disease) and its human counterpart nvCJD (new variant Creutzfeldt Jakob Disease). These and similar diseases are known as TSEs (Transmissible Spongiform Encephalopathies). TSEs afflict other species, most famously sheep (scrapie).
• Prions are pathogenic variants of proteins that are naturally produced in nerve cells and certain other
cells. The normal "healthy" prions are referred to as PrPc (Prion Protein cellular). The word "prion"
stands for "proteinaceous infectious particle" and so should properly only be applied to the
pathogenic variants. In this picture, the production of PrPc is illustrated from the nucleus at bottom
right. RNA that codes for PrPc is produced in the nucleus and exits via the nuclear pore. The RNA
then passes along ribosomes attached to the rER. PrPc is formed in the rER and then progresses up
through the Golgi. At the upper face of the Golgi, vesicles containing PrPc bud off and travel to the
cell surface. Here, they fuse with the cell membrane and so discharge their cargo at "PrPc". By this
means, the cellular proteins come to sit on the exterior of the cell.
• PrPc encounter rogue (purple) prions. These are termed PrPsc (sc stands for scrapie, the prion
disease of sheep). The rogue prions seem to force the normal proteins to change shape. Both types
of protein, the PrPc and their corresponding prions, are the same chemical - just different shapes. It
is this shape-flipping which is equivalent to the transmission of infection. Such a conformational shift
or flip could happen at the cell surface or in caveolae (one is shown as a small invagination in the cell
membrane). Residual PrPc might continue to be flipped by contact with the rogue conformations for
some time in these vesicles. Prions polymerise, finally appearing as purple fibrils in the picture at "P".
PrPsc is resistant to degradation by the enzymes contained in the lysosomes that are seen floating
nearby. Consequently, PrPsc accumulates in the cell. PrPsc vesicles may also travel to the Golgi and
intercept PrPc that is being processed there. In this way, PrPc particles could be switched to the
rogue form before they reach the surface of the cell. By such mechanisms, PrPc might be switched to
PrPsc at various points in and on the cell.
• Prions could enter the brain along the axons of neurons. This probably happens by a retrograde flow
of prion filled vesicles. These are shown in the picture as purple spheres ascending the axon like
elevators going up a shaft . Another route of entry could be the blood, probably in immune cells. A
lymphocyte is shown exiting the capillary at bottom left where it could then contact the astrocyte.
Astrocytes and other glial cells also support the production of prions.
BACTERIA
• Prokaryotic cells
•Features?
No nucleus – circular DNA
No membrane bound organelles
Very small
Mostly heterotrophic some autotrophic
Structure
Features
• Shaped – cocci, bacilli, spirilla
• Many are pathogenic, many not
• Cause disease by disrupting host cell’s;
producing powerful toxins; disrupting
host immune system
• Often defined by differential staining
• Gram positive (purple) and Gram
negative bacteria (pink/red)
Diseases
• Tetanus – Clostridium tetani
• Botulism - Clostridium botulinum
• Pneumonia - Pneumococcus
• Diphtheria
• Tuberculosis – Mycobacterium tuberculosis
• Food poisoning – Salmonella typhi, Staphylococcus aureus
• Throat infections - Streptococcus
• Typhoid fever
• Syphilis
• chlamydia
Reproduction
Binary fission
Treatment
• Antibiotics – natural eg penicillin or
synthetic
• Tetracycline
• Work by destroying bacterial structures
or cell membrane
Penicillium and bacterial inhibition
Fungal infections
• Cause many plant diseases e.g. Rust in
wheat
• In animals – ringworm, athletes foot, tinia,
thrush – usually not serious or life
threatening
• Mostly pathogenic in plants
• Transmitted via direct contact
Structure
Cell wall made of chitinNon motile usuallyFilamentous – have hyphaeProduce spores
Yeasts are a sub group –unicellular fungi - thrush
Yeast infection
Life-cycle
Protozoans
• Summarise Malaria parasite from text p
148
• Name pathogen, describe life cycle,
disease and treatment
Multicellular parasites - worms
• Flatworms – platyhelminthes
• Inhabits intestines of humans and other
animals
• May be up to 10m long
• Each segment in chain has
reproductive organs
• Round worms – nematodes
• Thread, pin, hook worms see p 162 text
