Lecture 2 Flashcards
what is a saprophyte
an organism that lives on dead or decaying matter can be plant, fungus, or microorganism.
Types of symbiosis (3)
Mutualism: both benefit Commensalism: they are neutral to eachother, neither damaging the other Parasitism: Only benefits the parasite/microorganism.
Whats the approx ratio of human body cells to the number of microbes it hosts?
1:10 located on skin, mucous membranes, gut, vagina
What are the benefits of commensual bacteria for humans and for the bacteria
Bacteria: Get shelter and food and a stable environment Do not penetrate or colonise into human tissues except for rarely through a wound or disease For the human: 1) Commensual bacteria prevent colonisation by harmful microbes, in a couple of ways: - occupy the surface and cover cell receptors the harmful bacteria would like to reach - Produce antimicrobial compounds, such as lactic acid in the vagina 2) Aid in digestion: Vitamin K and B12
Classes of parasitism (3)
Obligate : Are always found in defined host or hosts, are always pathogenic and never in normal flora Facultative : An organism which is often or usuallu parasitic but is not completely dependent on the host for completion of its life cycle, and may survive outside of it. May be a normal member of the flora, and may be pathogenic depending on the state of the host and microbe. examples: fungi or plant species parasitising other plants if the conditions are right. Opportunistic: An organism that is normally not parasitic and grows/lives in the environment of the host, but can take advantage and parasitize the host in certain conditions (ie immunosuppressed patients)
Predisposing factors for facultative or opportunistic infections
Stress. (physical or mental –> immune suppression) Wounds, burns Chronic debilitating conditions: Diabetes, alchol or drug abuse, malnutrition, tumors and immune suppression or chemotherapy Urinary tract obstructions
Medical related risk factors for generating opportunistic/facultative infecitons
Medical interventions: (Iatrogenic diseases) Antibiotics depleting normal GI flora Surgery wounds Prosthetics, catheters and Biofilm buildup.
Risk factors for opportunistic microbes What types of infections does a T-cel ldeficiency increase? B-cell deficiency?
Immune deficiencies of many different kinds. Weakened populations: Newborns, pregnant women, elderly T-cell deficiency -> increased intracellular pathogens, protozoa, helmiths B-cell deficiency -> increased bacterial, fungi, protozoa Acquired immune deficiencies: Immunosuppressive drugs, Radiation depletion of immune cells Tumors/Leukemia Viruses/infections of immune cells
Define Pathogenicity
The ability of the whole population of a microbe species to elecit disease in a given host or range of hosts
Is a genetically defined, qulaitative trait, ie. Is this microorganism capable of infecting this host species? yes/no
Define Virulence
A quantitative trait, defining the extent of disease or pathology caused by the microorganism in the host.
It is usually correlated with the ability of the microorganism to multiply within the host
Define the terms ID50 DL50 TCID50
What are these terms used for?
These terms are used to measure virulence.
ID50 Infective Dose: The number of microbes required under standard circumstances to induce disease in 50% of hosts.
DL50 Dosis Lethalis: Number that causes death in 50% of hosts
TCID50 Tissue Culture Infecting Dose: Quantity that damages 50% of tissue cultures.
Lower values indicate higher virulence
What is the structure of LPS?
Lipid A: A disaccharide diphosphate, each separate glucose, O- and N-acetylated with a different pair of fatty acids. 6 total FA chains.
the Core polysaccharide
and the repeated O-antigen, a 4-monosaccharide unit that is repeated 40 times.
What is Horizontal Transmission of infection and its categories?
What is Vertical transmission?
Horizontal from within one genration, as opposed to vertical, which is down the generation line, mother to child. Transplacental
Means of spread:
Direct contact
Indirect contact: by contaminated objects
Vehicles:
- Air, aerosolized pathogen in sneezes, coughs, breath
- Water or food sources
- Vectors: blood sucking insects
- Vertebrate reservoirs: other humans or animals which are constantly harboring the disease, ex. rats or dogs/cats.
Iatrogenic infections
direct transcutaneous (also called percutaenous) transmission by contaminated hospital/medical equipment.
What does the Incubation Time of a pathogen indicate?
The period of time from the moment of infection to the onset of symptoms.
What can be one affect of symptomless childhood infections on the patient as an adult (according to our lectures very important…)?
They may obtain lifelong immunity or cross-immunity.
examples: toxoplasmosis and HSV-1/HSV-2
What are some categories of symptomless infections?
Latent - a pathogen remains in the body inactive, and activates upon certain intrinsic or extrinsic factors
Persistent - viruses are persistent if they remain in the body symptomless and is regularly goes through cycles of inactivity and activity, reproducing and shedding viruses, but the shedding is symptomless
Carrier - The pathogen is continuously shed without symptoms.
What are the bodies nonspecific defenses against microbes?
(not the innate immune system)
Physical and chemical means of inhibiting microbe entry/survival
- Skin, physical barrier and the presence of organic acids
- Outward cilia movement of the respiratory tract
- low pH in the GI tract
- antimicrobial sebum (earwax)
- lactic acid of the vigina
- lysozymes and other enzymes of tears and saliva
- high osmolality of urine
What are the recognized structures of the innate immune system macrophages?
What receptors bind these structures?
PAMPs and DAMPs, bound by C-type lectins, and TLRs TLR1, 2, 4, 5, 6, which can be Endosomal or Cell Surface receptors
Pathogenic associated molecular patternsm, PAMPs:
From GrPos bact: G+ cell wall peptidoglycan, lipoteichoic acid
From GrNeg bact: LPS
From either: Flagellin, N-formylmethionine, hypometheylated CpG-DNA, free single or double stranded DNA or RNA
Damage associated molecular patterns, DAMPs:
Components of cells that should be intracellular but are encountered by the macrophages in the environment (from lysed/dead cells)
Nuclear proteins
Mitochondrial DNA
Oxygen radicals
Heat shock proteins
What is the antigen expression pattern of NK cells?
What are the multiple means by which NK cells can kill their target?
TCR+ CD16+ (Fc receptor+)
MHC negative
NK cells can kill by
1) Binding their Fas Ligand to the FasR apoptosis inducing receptor on target cells
2) Inserting perforin proteins into the target cell membrane
3) By releasing granzyme vesicles/granules onto their target cells (serien proteases)
What is the antigen profile of Cytotoxic vs. Helper T-cells?
What MHC classes do each of them interact with?
T-helper cells: CD4+ interact with MHC-II
-Helper cells bind MHC-II-bound antigen complexes, MHC-II is only expressed by APCs, and presents exogenous antigens, things that have been eaten by the macrophages and are bound by the MHC-2 receptor from within endosomes, and are being presented to ativate the immune system by the T-helpers.
Cytotoxic T cells: CD8+ with MHC-I
-Cytotoxic T cells bind MHC-1 bound antigen complexes. MHC-1 is expressed by every nucleated cell in the body. MHC-1 presents antigens from intracellularly derived proteins that have been degraded by the proteasome. They are presented by MHC-1 to recruit CD8+ cells signalling that “I’m infected, or I’m cancerous,” and needing Cytotoxic cells to kill them.
Which cells are involved in humoral immunity and which are involved in cellular immunity?
Cellular immunity : T-cells, NK cells, macrophages, neutrophils
Humoral immunity : B-cells
What are the classes of antibodies?
What is their order of produciton during an infection and what a re their main targets?
IgM: produced first, rapid and transient effect. Pentamer
IgG: Produced next, and then produced lifelong at low levels by plasma B cell clones, for rapid re-expression in case of re-infection. Monomer
IgA: produced on mucous membranes to prevent microbes binding to them, bind lipoteichoic acid and bacterial pili. Dimer
IgD: only about 0.25% of antibodies are IgD, not a real clear funciton, monomer, but it is ancient and well conserved through species so clearly important. Monomer
IgE: produced in allergic and antiparasitic reactions. Monomer
What are some ways viruses evade or defeat immune system?
By replicating in immune cells (HIV)
By episomal persistence or integrating (retroviruses)
By Cell-to-cell spread remaining intracellular, avoiding antibodies
Antigen variation - rapidly changing/mutating (influenza viruses)
Inhibiting MHC synthesis (adenovirus)
Mimicing interleukins (Epstein-Barr virus)
Neutralizing complement fragment C3b (HSV-1)
What is the difference between Protozoa and Helminths?
Protozoa are single celled, Helminths are multicelled
