RC Test 4 > B4.072 Streptococcus Pneumoniae > Flashcards

B4.072 Streptococcus Pneumoniae Flashcards

(61 cards)

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1
Q

what are bacterial capsules made out of

A

polysaccharides

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2
Q

who cannot mount an Ab response against bacterial capsules?

A

< 2 y/o

not full response until age 6

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3
Q

what functions of the immune system are reduced by capsules

A

opsonization and phagocytosis

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4
Q

what immune cells don’t react to capsules?

A

T cells

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5
Q

which antibody classes are produced against capsules

A

IgM

IgG2

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6
Q

issue with IgM against capsule

A

activates complement but has low affinity

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7
Q

issue with IgG2 and capsule

A

poor at opsonization

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8
Q

which bacteria produces a hyaluronic capsule

A

Group A strep

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9
Q

what is the issue with the hyaluronic acid capsule

A

weakly immunogenic
similar to hyaluronic acid in connective tissue
may bind to CD44 in pharynx

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10
Q

what is tricky about the type B Neisseria meningitides capsule

A

contains sialic acid residues, similar to those in human cells
inhibits Ab production and alternative complement pathways

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11
Q

what is slime?

A

a carb coat around bacteria that can be less well defined than a capsule
viscous and sticky

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12
Q

what is the function of slime?

A

allow bacteria to attach to surfaces (catheters, teeth)

can be used to glide

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13
Q

generic term for capsules or sline

A

glycoalyx

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14
Q

bacillus anthracis capsule composition

A

poly D glutamic acid

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15
Q

what are used to serotype bacteria

A

capsule

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16
Q

what is the downside to serotyping bacteria by capsule?

A

S.pneumo and N.meningitides can swap capsule types between strains

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17
Q

how can capsule types be swapped?

A

transformation

bacteria take in DNA from the environment (from dead, pathogenic s.pneumo)

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18
Q

bacteria that can naturally carry out transformation

A

competent

s. pneumo is competent

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19
Q

what % of pathogenic strains of s.pneumo have a capsule

A

100%

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20
Q

aside from evading immune system, how else can capsules help bacteria survive?

A

prevent desiccation

able to survive in harsher environments

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21
Q

which immune functions are inhibited by the difficulties of producing Abs to bacterial capsule

A

T cell responses
antibody opsonization
activation of classical complement pathway

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22
Q

how are t cell responses inhibited by capsules

A

carbohydrates not presented by MHC to T cells (too similar to what is native to our bodies)

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23
Q

how is antibody opsonization inhibited by capsules?

A

can respond to carbs, but just not good at opsonizing it

don’t develop memory B cells

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24
Q

how do we eventually produce immunity to encapsulated bacteria?

A

when they die, they expose their protein content
immune response is produced to this protein content
becomes protective at age 6

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25
major encapsulated pathogens
s. pneumo k. pneumoniae Hib p. aeruginosa n. meningitides Cryptococcus neoformans (yeast)
26
how do pneumococci invade?
spread by aerosol harbored in nasopharynx interaction most commonly leads to clearance and serotype-specific immunity
27
common pneumococcal manifestations in children
otitis media
28
invasive pneumococcal disease
spread to lungs and bloodstream
29
most serious development of pneumococcal disease
meningitis
30
what molecules allows for invasion of pneumococcus at the cellular level
phosphorylcholin (PCho) | on cell wall of teichoic acid of pneumococci
31
what is the function of PCho?
mimics PAF and binds to host cell PAFr | leads to uptake of bacteria into a vesicle and transmigration across epithelial or endothelial barrier
32
what works against this PCho binding and bacterial entrance?
innate immune elements CRP binds to PCho on bacteria surfactant contains abundant PCho inhibit bacterial contact with host cell
33
what are vaccines against capsulated pathogens based on?
immunity to the capsule
34
who cannot produce protective Abs to capsular vaccines?
young children
35
how are vaccines against capsulated pathogens made?
capsular polysaccharide is conjugated to another immunogenic molecule (diphtheria toxoid, tetanus toxoid)
36
how does the immunogenic molecule help the body produce a response to the polysaccharide capsule?
generates a strong T cell response and class switches Abs to produce memory response against carbohydrates
37
how is the polysaccharide capsule processed and responded to when it is unconjugated?
cross links BCR on B cells drive production of IgG2, IgM not very useful no memory response
38
how is the polysaccharide capsule processed and responded to when it is conjugated?
processed by polysaccharide specific B cell peptides are presented to carrier peptide specific T cells results in T cell help for production of both plasma cells and memory B cells
39
which pathogens have conjugated vaccines in place?
s. pneumo n. meningitides Hib influenza
40
leading cause of CAP
s. pnuemo 900,000 per year in US kills 50,000 kids worldwide per year
41
what groups are particularly susceptible to s.pneumo pneumonia
alcoholic and HIV patients
42
why are HIV patients at high risk for s. pnuemo when the response is primarily from B cells and neutrophils, not T cells?
need T cells to activate B cells and stimulate them to produce Abs or class switch
43
characteristics of s. penumo
``` gram + cocci that grow in pairs/chains a hemolytic catalase neg positive quelling test soluble in bile salts susceptible to optochin ```
44
pathophysiology of illness from s. pnuemo
invasive disease may occur upon acquisition of a new epithelium serotype strong association with viral illnesses viral infections increase pneumococcal attachment to receptors on activated respiratory epithelium
45
what is pneumolysin?
produced by s. pnuemo toxic to mammalian cell membranes by inducing pored can induce lysis in neutrophils
46
predisposing conditions for pneumococcal infection
``` overcrowded conditions age (old or young) alcohol viral illness immunodeficiency ```
47
what causes pneumococcal symptoms?
largely due to inflammatory response - can cause pain by increasing pressure (otitis media) - interfere with oxygenation of blood (pneumonia) - -interfere with cerebral function (meningitis)
48
distinctive symptoms and signs of pneumococcal pneumonia
cough and rust colored sputum fever radiographic infiltrate
49
WBC findings in pneumococcal pneumonia
exceeds 12,000 in majority of pts | neutrophil leukocytosis
50
what % of pneumonia infections have pos blood cultures
25%
51
2 key factors in immunity against s. pneumo
phagocytosis by neutrophils | MAIN: opsonization by Ab or complement
52
discuss the differences in opsonization in naïve vs exposed individuals
naïve: poor response | exposed: protective IgG and IgA
53
what substances are found in the s. pneumo wall and what can they do?
teichoic acid peptidoglycan C substance -all can activate alternative complement pathway (CRP can too)
54
why does s.pneumo produce an IgA1 protease?
IgA can activate alternative complement cascade IgA1 is the predominant form of Ab found in the blood inhibits this immune response
55
main defense mechanisms for s.pneumo
1. pneumolysin 2. IgA1 protease 3. capsule - inhibits innate an acquired immunity - prevents T cell immunity - inhibits phagocytosis due to lack of suitable Ab or complement - prevents CRP binding to PCho and activating complement 4. competency
56
why is TLR9 important?
detect unmethylated CpG from bacteria/viruses | when s.pneumo is broken down, DNA is released and taken up by phagocytes, interacts with TLR9 to mount immune response
57
how does s.pneumo stimulate macrophages and dendritic cells?
TLR2 (peptidoglycan and lipopeptides)
58
acute phase response
fever raised CRP raised ESR
59
what can TLR9 eventually activate?
dendritic cells | leads to production of IL-12, TNFa, IL-6, IL-1
60
which cytokines produce Th17 cells?
IL-23 TGFB IL-6 (main one in acute phase)
61
what do Th17 cells do
activate neutrophils

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