Immunology Flashcards
(131 cards)
1
Q
Why are viruses not cells in their own right and what are they, if not cells?
A
Because they require a host cell to replicate
Obligate parasites
2
Q
Can viruses infect bacteria?
A
Yes
3
Q
List the main types of infectious agents causing disease in humans
A
Viruses Bacteria Fungi Protozoa Helminths
4
Q
Describe how viruses replicate
A
Host Cell Machinery
Divide by budding out of host cells, or cytolysis
5
Q
What makes HIV a retrovirus?
A
RNA used to make DNA via Reverse Transcriptase
Whereas normally in viruses DNA makes RNA which makes the protein
6
Q
Recall an example of a virus
A
Smallpox (Variola Virus), influenza, HIV…
7
Q
What makes Prokaryotes more susceptible to the effects of a mutation?
A
They are haploid, so if one gene is mutated, the effect will occur
However, in a diploid cell, the mutation must be seen on both copies of DNA to occur
8
Q
What is the main component of Prokaryotic cell walls?
A
Peptidoglycan (murein)
9
Q
How do Prokaryotes divide?
A
Binary Fission
10
Q
What are the purposes of the pili (several pilus) on Prokaryotes
A
They can have a role in movement, but are more often involved in adherence to surfaces, which facilitates infection, and is a key virulence characteristic
11
Q
Why are the mutation rates of viruses higher than humans?
A
They have half the point mutation rate as they have error-prone replication and cannot deal with errors in genetic code efficiently
Much shorter replication times (20 mins vs 26 yrs)
12
Q
Based on the location of the infection, what three groups can Fungi be divided into?
A
Cutaneous - typically involving the skin, hair, and nails
Mucosal - oral, gastrointestinal, vaginal
Systemic Mycoses - affecting internal organs
13
Q
Which two forms can fungi exist in during their lifetimes?
A
Yeasts
Filaments
14
Q
How do Protozoa replicate?
A
Replicate in a host by binary fission
Or
by formation of trophozoites inside a cell
15
Q
How is Protozoa infection acquired?
A
Ingestion
Or
through a vector
16
Q
What does Metazoa mean?
A
Contains cells that are differentiated into tissues and organs
17
Q
What type of organisms are Helminths?
A
Multi-cellular and eukaryotic
18
Q
What is the adaptive immune system compromised of?
A
T cells (CD4, CD8, T regulatory cells) B cells (B lymphocytes and plasma cells)
19
Q
What are the hallmarks of adaptive immunity?
A
Specificity
Memory
20
Q
What do BCR and TCR stand for respectively?
A
B cell receptors
T cell receptors
21
Q
Name the 3 types of lymphocytes
A
B cells
T cells
NK (Natural Killer) cells
22
Q
What is meant by a primary lymphoid organ?
A
Organs where lymphocytes are produced - Lymphopoieses
23
Q
List 3 primary lymphoid organs
A
Thymus
Bone marrow
Fetal liver
24
Q
What do CD4 (T-helper cells) do?
A
Produce lots of cytokines that guide B cells and other T cell responses
25
What do CD8 (cytotoxic T cells) do?
Actively kill foreign antigen-expressing cells
26
What is the primary site of hematopoiesis?
Bone marrow
27
What are the roles of the red and yellow bone marrows respectively?
Red - Produces blood cells
| Yellow - Fat stores
28
What are immature T cells known as?
Thymocytes
29
Where do immature T cells migrate from the bone marrow to?
Thymus
30
Where do B cells migrate to in the immature stage for differentiation?
Spleen
31
Describe what is meant by 'repertoire' in terms of lymphocytes
The range of genetically distinct BCRs or TRCs present in a given host
The larger the repertoire, the more threats can be recognized
32
What is thymic involution?
The shrinkage of the thymus with age → associated with a change in structure and a reduced mass
33
Where is the thymus?
On top of heart, above lungs in the thoracic cavity
34
What are the 3 steps in the stepwise differentiation of T cells?
- Positive selection - can the T cell receptor signal? (Does it see the MHC receptors on the surrounding cells?)
- Negative selection - does it react against our own body (if does react against self-antigens then it undergoes **selective apoptosis**)
- Final selection and exit
35
What is meant by a secondary lymphoid organ?
Where lymphocytes can interact with antigens and other lymphocytes to guide their activation and differentiation
36
List some secondary lymphoid organs
Spleen
Lymph nodes
Appendix
Mucosal associated lymphoid tissue
37
Where in the lymph nodes generally are the T cells found relative to B cells?
T cells - Towards inside (further from the marginal sinus)
| B cells - Towards outside (closer to the marginal sinus)
38
What do the words afferent and efferent refer to respectively?
Afferent - Lymphatic vessels (into)
| Efferent - Lymphatic vessels (out of)
39
What is it that makes the spleen so good at filtering antigens from the blood?
It is **highly attached** to the arterial circulation via the **splenic artery**
So it can filter blood rapidly and in **large numbers**
40
What is the first line of defense against infection?
Epithelial barriers
41
What are Peyer's patches and where are they found?
```
Specialized secondary lymphoid tissues
Specialized Microfold (M) cells sample antigen directly from the lumen and deliver it to antigen-presenting cells
Below epithelium of the ileum of the small intestine
```
42
Define a germinal center
Anatomically restricted site where B cells undergo mutation and selection to generate high-affinity antibodies
43
- Describe how lymphatic drainage occurs at gut-associated lymphoid tissue
Intraepithelial **lymphocytes** enter villi
These are drained to **mesenteric lymph node**
The **afferent** lymphatic vessels at Peyer's patch pick these up
The follicle is highly enriched with **B cells**, and contains a high frequency of **germinal centers**
44
Why is the intestine so enriched for these germinal centers?
High amount of antigen being provided in the form of microbial products from the microbiota of the intestinal tract
45
How do specific T cells become activated by their specific antigen which is in a different part of the body?
Each naive T cell recirculates once every 24 hours
They enter Lymph nodes with antigens (lymphatic vessels)
Become activated by binding to antigens from lymphatic vessels
Leave via efferent lymphatic vessel
Travel from peripheral tissue and inflammation occurs
The lymphatic vessels enter the lymph node via the afferent lymphatic vessels
46
What are the 2 steps involved in the extravasation of naïve T cells into lymph nodes?
Selectin binding
Integrin binding
(The process involves rolling, activation, arrest/adhesion, and transendothelial migration)
47
Define antigen presentation
The display of peptides in the major histocompatibility complex (MHC) I or II proteins such that the T cell receptor can attempt to bind them
48
How do Dendritic cells transport antigens from the site of inflammation to the secondary lymphocyte tissues?
Once dendritic cells uptake antigen they migrate out of the inflamed tissue into lymph nodes and carry antigen towards the T cells and B cells
49
How else can the antigens be transported to the secondary lymphatic tissues?
If there is a great concentration of antigen, it will be present in the fluid built up during the inflammatory response, which will be drained into the lymphatic system and will eventually reach a secondary lymphatic tissue.
50
What are the 3 types of bacteriological tests and what does each test identify?
Microscopy (Gram stain) - Which type of bacteria
Culture - Which species of bacteria
Sensitivities - Which treatment should be used
51
What color are gram-negative bacteria and what does it consist of?
Pink
| 2 outer membranes with a thin peptidoglycan layer in the middle of them
52
What color are gram-positive bacteria and what does it consist of?
Purple
| 1 outer membrane with thick peptidoglycan around it
53
Which part of a bacterial cell envelope "holds" the Gram stain?
Peptidoglycan
54
In what order are the gram stain substances applied?
Crystal violet stain (purple stain)
Iodine (to form crystallizations and stiffen up the peptidoglycan chains)
Alcohol (to wash and decolorize the bacteria)
Safranin stain (pink stain)
55
What is the purpose of the alcohol washes in gram staining?
Dehydrates the peptidoglycan area resulting in it becoming tighter
56
What makes gram-positive purple?
Alcohol causes the peptidoglycan layer to thicken and tighten hence the crystal and iodine complexes can't be washed out hence remains stained with crystal violet and appear purple
57
Why do gram-negative bacteria stain pink?
Alcohol washes out crystal violet and iodine as there is only a thin peptidoglycan layer
Safranin then stains bacteria pink.
58
What shape does coccus describe?
Sphere
59
What shape does bacillus describe?
Round-ended cylinder
60
How would you describe the shape of coccobacilli?
Oval-like
61
Describe the shape of diplococci
Spherical in pairs
62
What is hemolytic activity useful in differentiating between?
Gram-positive bacteria → Staphylococcus, Streptococcus, Enterococcus
63
What does the hemolytic activity test for?
The capacity of microorganisms to produce hemolysins (enzymes that damage red blood cells)
64
List and describe the results of the hemolysis test
Gamma - no hemolysis
Alpha - partial (opaque zone)
Beta - complete hemolysis (transparent greenish zone)
65
What is the major cause of hemolysis in newborn babies?
Group B Streptococcus or Streptococcus agalactiae is the commonest cause of meningitis in babies under 3 months
66
Outline how to complete the hemolytic activity test
1. Pick a bacterial colony from an agar plate.
2. Streak out the bacterial colony onto medium containing 5% sheep red blood cells.
3. Incubate plate overnight and assess activity next day.
4. What we assess are the affect of the bacteria on the red blood cells.
67
What type of agar is used for the lactose fermentation test?
MacConkey agar - containing bile salts, crystal violet, and lactose
68
What is the lactose fermentation used for?
Differentiating gram-negative bacteria (more specifically, between species of Bacilli)
69
What does the lactose fermentation test measure?
The difference in pH to determine whether bacteria is fermenting or non-fermenting
70
What are the results for a lactose-fermenter?
Agar plate shows pink colonies after being incubated overnight
71
What are the results for a lactose non-fermenter?
Colorless (yellow) colonies on the agar plate
72
What does the catalase test determine?
Determines whether a bacteria produces catalase
73
What does catalase break down?
Hydrogen peroxide
74
What does the catalase test discriminate between?
Staphylococci (produces catalase)
| Streptococci (doesn't produce catalase)
75
What are the results for catalase-positive and catalase-negative?
Catalase + = Oxygen bubbles
| Catalase - = no oxygen bubbles
76
What is coagulase?
An enzyme that cross-links fibrinogen in plasma to form a clot on the bacterial surface
(processes factor 2 to 2a. Thrombin cleaves fibrinogen into fibrin. Factor 8a crosslinks fibrin to form fibrin clots)
77
What can coagulase be used to discriminate between?
S. aureus (produce coagulase) and other staphylococci (don't produce coagulase)
78
Describe the results of coagulase-positive and negative
Coagulase + = clumps
| Coagulase - = no clumps
79
Outline the steps for the coagulase test
1. Apply bacteria onto a slide
2. Apply plasma
3. Incubate for 15 seconds and gently rotate
4. Generation of clumps if coagulase +
80
List the names of some diplococci and what gram stain they are
N. gonorrhoeae
N. meningitidis
M. catarrhalis
All **Gram negative**
81
```
Which of these species gives a positive coagulase test?
Staphylococcus epidermidis
Staphylococcus aureus
Staphylococcus lugdenesis
Staphylococcus hemolyticus
```
Staphylococcus aureus
82
Define antibiotic
An antimicrobial agent produced by a microorganism that kills or inhibits other microorganisms.
Target many different bacterial processes and are SELECTIVELY TOXIC
83
What are most antibiotics used today produced by?
Soil-dwelling fungi or bacteria
84
Define antimicrobial
A chemical that selectively kills or inhibits microbes
85
Define bactericidal
Kills bacteria
86
Define bacteriostatic
Stops bacteria growing
87
Define antiseptic
Chemical that kills or inhibits microbes, that is used to prevent infection.
88
What was the first example of sulphonamide antibiotic?
Prontosil
89
What is prontosil used to treat?
Urinary tract infections
Respiratory tract infections
Bacteremia
Prophylaxis for HIV + individuals
90
What are the reasons why antibiotic resistance may lead to increased mortality, morbidity, and cost?
Increased time to effective therapy
Requirement for additional approaches e.g - surgery
Use of expensive therapy (newer drugs)
Use of more toxic drugs e.g- vancomycin
Use of less effective 'second choice' antibiotics
91
Give 2 examples of aminoglycosides
Gentamicin
| Streptomycin
92
What processes do aminoglycosides target?
Protein synthesis
| RNA proofreading
93
What part of a cell do aminoglycosides cause damage to?
Cell membrane
| Lack of proofreading activity leads to aberrant protein production
94
What ribosomal subunit do aminoglycosides target?
30S
95
Are aminoglycosides bactericidal or bacteriostatic?
Bactericidal
96
What has lead to an increasing use of aminoglycosides?
Resistance to other antibiotics
97
What is the mechanism of rifampicin?
Targets RpoB subunit of RNA polymerase, inhibiting transcription (bactericidal)
Spontaneous resistance is frequent
98
What color does rifampicin make your secretion go?
Orange/red (affects patient compliance)
99
What is the mechanism of vancomycin?
Targets Lipid II component of cell wall biosynthesis and wall cross-linking via D-alanine residues
Bactericidal
100
What has lead to an increasing use of vancomycin?
Resistance to other antibiotics e.g. against MRSA
101
What type of bacteria does linezolid affect?
Gram-positive bacteria
102
What is the mechanism of linezolid?
Inhibits the initiation of protein synthesis by binding to 50S rRNA subunit (bacteriostatic).
103
What limits the dose of daptomycin?
Toxicity
104
What is the mechanism of daptomycin?
Bactericidal - targets the bacterial cell membrane
105
What type of bacteria does daptomycin affect?
Gram-positive bacteria
106
Give 2 examples of beta-lactams
Penicillin
| Methicillin
107
What is the mechanism of beta-lactams?
Interfere with the synthesis of the peptidoglycan component of the bacterial cell wall (bind to penicillin-binding proteins)
Bactericidal
108
Give 2 processes that are unique to bacterial cells
Production of peptidoglycan
| Maintenance of lipopolysaccharide (LPS) layer of gram-negative bacteria
109
Give 2 examples of macrolides
Erythromycin
| Azithromycin
110
What types of infections can macrolides be used against?
Gram-positive
| Some gram-negative infections
111
Describe the mechanism of macrolides
Targets 50S ribosomal subunit preventing amino-acyl transfer, therefore truncating polypeptides, preventing growth
Bacteriostatic
112
What do quinolones target in gram-negative bacteria?
DNA gyrase
113
What do quinolones target in gram-positive bacteria?
Topoisomerase IV
114
What do quinolones targeting DNA gyrase in gram-negative bacteria and topoisomerase IV in gram-positive bacteria do to the bacteria?
Result in DNA damage and the death of the bacteria.
| Bactericidal
115
What is meant by resistance?
If a bacterium can grow at or above the breakpoint concentration (minimal inhibitory concentration of antibiotic)
116
Why might there be more of a resistance to penicillin in hospitals than in the community?
Routine use of penicillin in hospitals provides a selection pressure
For the acquisition and maintenance of resistance genes
117
What are the 4 distinct mechanisms by which antibiotic resistance can occur?
Altered target site
Inactivation of antibiotic
Altered mechanism
Decreased drug accumulation
118
Give 2 examples in which a target site can be altered
MRSA encodes alternative PBP with a low affinity for beta-lactams
Acquisition of erm gene by streptococcus pneumoniae encodes an enzyme that methylates antibiotic target site in 50S ribosomal subunit
119
How does the inactivation of antibiotics occur?
Enzymatic degradation or alteration, rendering the antibiotic ineffective
120
What is one of the greatest threats to antibiotic use at the moment?
Bacteria that encode broad spectrum of beta-lactamase enzymes
Such as ESBL and NDM-1 which can degrade a wide range of beta-lactams
121
How does the altered metabolism pathway occur within antibiotic resistance?
Increased production of an enzyme substrate can outcompete the antibiotic for the target site
Or bacteria can switch to other metabolic pathways.
122
How does decreased drug accumulation occur?
Decreased antibiotic cell permeability to the antibiotic and/or
Increased number of efflux pumps to keep the antibiotic out of the cell
Makes it so that the drug does not reach the concentration required to be effective
123
What are the 3 sources of antibiotic-resistant genes and how do they work?
Plasmids - extra, chromosomal circular DNA often carry
multiple copies and often carry multiple antibiotic-
resistant genes so selection for one maintains
resistance for all. Can be transferred between bacteria
Transposons - integrate into chromosomal DNA and
allow transfer of genes from plasmid to
chromosome and vice versa
Naked DNA - DNA from dead bacteria released to the
environment can be taken up by many bacteria
124
Describe the 3 ways that bacteria can spread their antibiotic-resistant genes
Transformation - uptake of extracellular DNA
Phages - viruses infect bacteria and take up some of
their DNA and then go on to infect other bacteria,
passing on the DNA
Conjugation - bacterial sex to share plasmids between
them (pilus-mediated DNA transfer)
125
Give some of the non-genetic mechanisms of resistance/treatment failure
Biofilm - matrix encased communities of bacteria that
are highly drug-tolerant
Intracellular location - some bacteria persist inside
human cells, making it harder for antibiotics to get
to bacteria
Slow growth - hard for antibiotics to inhibit replication
processes if bacteria don't use them as often
Persisters - dormant bacteria that are not carrying out
the processes that antibiotics inhibit
Spores - extremely resistant to hear, antiseptics, and
antibiotics
126
In what sectors are antibiotics used more?
Critical care
| Wards
127
What are some of the risk factors for HAI?
High number of ill people
Crowded wards
Presence of pathogens
Broken skin - surgical wound/IV catheter
Indwelling devices - intubation
Antibiotic therapy - may suppress normal flora
Transmission by staff - contact with multiple patients
128
How might antibiotic therapy impair commensal flora?
Antibiotic therapy removes commensal organisms
The pathogen has no competition leading to overgrowth
The pathogen produces toxins and damages host-symptomatic infection
Spreads to other patients
129
Give some of the methods we might use to address resistance
Prescribing strategies - tighter controls, temporary
withdrawal of certain classes, and restrictions of
antibiotics for certain serious infections
Reduce the use of broad-spectrum antibiotics
Quicker identification of infections caused by resistant
strains
Combination therapies
Clinicians should have knowledge of local strains and
resistance patterns
130
What 3 broad classes of conditions are caused by fungi?
Allergy - allergic reactions to fungal products
Mycotoxicoses - ingestion of fungi or their toxic products
Mycoses - superficial, subcutaneous, or systemic colonization, invasion, and destruction of human tissue
131
What do fungi use in their cell membrane instead of cholesterol?
Ergosterol
