Immuno Flashcards
TQ
-Acquired through placental IgG transport, breast feeding IGA
Passive + natural vaccination
active=acquired through recovery from infx
-Acquired through IV injection of anti-serum
Passive + artificial vaccination
active=immunization w/ vaccines
-Do not PREVENT infx, rather reduce severity of dz
»Th2 response
-Only rabies and hepatitis are therapeutic
-Primes immune response vs pathogen so that when you encounter it, you can fight it quickly w/ Abs & memory cells
Vaccines
directed at Ag epitopes»adaptive immunity
What kind of vaccine is…
Oral polio, varicella; mumps, measles, rubella, bacillus Calmette-Guerin (BCG)?
Live attenuated
What kind of vaccine is…
Inactivated polio
Killed/inactivated
can be used anytime
What kind of vaccine is…
Diphtheria toxoid, tetanus toxoid
Subunit
only some Ags
What kind of vaccine is…
Hep B
Recombinant subunit
Ags are recombinant
What kind of vaccine is…
Haemophilus influenzae type b, Streptococcus pneumoniae
Conjugate (polysaccharides-protein)
Streptococcus pneumoniae can also be given in polyvalent form (large # of Ags)
Passive immunization:
Ab from other species may cause systemic anaphylaxis (IgG)…otherwise known as what?
OR
May induce type III hypersensitivity with activation of complement in the tissues
serum sickness
Active immunization:
IM inactivated & live attenuated influenza vaccine & yellow fever vaccine are grown in chicken eggs…What does this pose a risk for?
allergic rxn if egg allergy
- Infant immunity is not competent»infx
- Incr morbidity in neonates due to what?
- Bacteria: group B streptococci & E. coli
- Viruses: HSV, CMV, VZV, RSV (decr Th1)
- Fungi: Candida
Is cell-mediated immunity transferred from mother to fetus?
NO, humoral is!
Infants rely on their own T cells to fight pathogens and respond to vaccination
TQ
Neonates have delayed IL-2 producing DC and therefore have impaired…
Th1 responses
How does cell mediated immunity work?
Th1 initiated when DC or Mφ eat pathogen»
IL-12 stim NK cells incr Th1 effector cells»???
IFN-γ»
Activates Mφ» pro-inflam cytokines IL-1β, TNF-α, IL-12.
(IFN-γ also promotes pathogen killing by macrophages)
TQ
Vaccination in newborn…low T cell response*
What are some examples?
High response to BCG though!
- (HBVac) or oral poliovirus (OPV) vaccines»Th1 type responses that are lower than those seen in adults
- Diminished delayed-type hypersensitivity (DTH) skin test reactions to Ags such as candida and tetanus toxoid
Abs against bacteria are directed against what?
cell wall Ags
What is the principal mechanism of defense against TI polysaccharide-rich Ags of encapsulated bacteria?
Humoral immunity
What is the major protective immune response against extracellular bacteria?
Humoral immunity
Blocks infx, eliminate microbes, neutralize toxins, phagocytosis, complement activation
TQ
Why were conjugate vaccines made?
To overcome the poor response to polysaccharide Ags by complexing polysaccharide Ags to immunogenic proteins, thus converting them into “T cell-dependent” Ag.
IgA, IgM, IgD, and IgE do NOT cross the placenta. If elevated IgM or IgA are seen in cord blood, what does this suggest?
Intrauterine infx
Which Ig rises rapidly 1 mo after birth as a response to the massive antigenic stimulation present in new environment
IgM
TQ
Why is their a higher frequency of gram-negative infxs in newborns?
IgM isn’t effective as Ab produced later…doesn’t provide sufficient heat-stable opsonins
TQ
Which infants have low opsonic activity for all types of organisms?
Premature infants (receive less maternal IgG)
-Many bacterial polysaccharides of encapsulated bacteria are TI Ags.
What is the major mechanism of host defense against infx against encap bacteria?
Humoral immunity
Transient hygogammaglobulinemia of infancy…most of the Igs are from mom’s IgG, but are higher/lower than moms (baby + mom). Premature infants have lower IgG.
higher
TQ
Full-term neonates produce Ab to TD protein Ags such as tetnus and….
- diphtheria toxoids
- hepatitis B surface Ag
- OPV
TQ
Responses to TI Ags (polysaccharide) are severely blunted until approximately 18 to 24 months of age. What are some examples?
Capsular polysaccharides of:
- H. influenzae type b
- Group B streptococci
TQ
Why were conjugate vaccines made?
Overcome the poor response to polysaccharide Ags by complexing polysaccharide Ags to immunogenic proteins, thus converting them into “T cell-dependent” Ag.
- Memory cells are generated in germinal centers for T-dep protein Ags
- Memory cells are 1 of 4 types of B-cells. What are the 3 others?
- Antibody secreting cells
- Isotype switching cells
- Affinity maturation cells
- TD Ags (proteins) and TI Ags (nonproteins) induce Ab responses with different characteristics.
- The differences largely reflect the influence of Th cells in the responses to protein Ags. What are some differences?
TD-Ag–>isotype switching, affinity maturation, and memory B cells
TI-Ag–>low switching, no affinity maturation, no memory B cells
-Many non-protein Ags (polysacc and lipids) stimulate Ab w/o Th cells
What are these Ags cells called?
Abs to these Ags are of low affinity and consist mainly of IgM, with limited isotype switching.
Thymus independent (TI)
Most TI Ags are multivalent=composed of many identical Ag epitopes. Why is this impt?
Maximal cross-linking of the BCR complex on specific B cells»
Activation without T cell help!!
TQ
Why is an asplenic pt at incr risk for encapsulated bacterial infx ?
Spleen has marginal zone B-1 cells (non-circ mature B cells) that are impt in Ab responses to TI antigens, mainly polysaccharides…produce IgM
How are TI Ags (polysaccharides, glycolipids, and nucleic acids) processed?
Activate complement system by the alternative pathway»generating C3d»binds Ag»recognized by CR2 on B cell.
-Some TI non-protein Ags can induce Ig isotypes other than IgM
Ex: pneumococcal capsular polysaccharide induces which Ab?
IgG2
- TI Ags contribute to their generaton
- In circulation of normal individuals and produced w/o exposure to pathogens
- low-affinity anti-carb Abs, produced by peritoneal B-cells (GI bacteria) and MZ B-cells (spleen)
Natural Ab
TQ
-Effective vaccines must induce both affinity maturation & memory B cell formation (only happens if vaccine activates Th cells)
-How then do you design vaccines for capsular polysacc which cannot stim T cells?
What are these vaccines called ?
Conjugate vaccines
- polysacch linked to foreign protein=hapten-carrier conjugate
- Induces high-affinity Abs and memory cells
notes:
T cell=specific for carrier protein
B cell=polysacch specific
How does the newborn’s immune sys cope w/ the surge of proinflam signals towards commensal bacteria at birth?
D71+ erythroid cells in neonatal human cord blood»immunosuppression via arginase-2
allows infants to adapt!
TQ
What is arginase-2
Enzyme that impairs innate immune responses, including prod of Th1-promoting TNF-a
TQ
What challenges the idea that the suscept of neonates to infx is due to immune-cell-intrinsic defects?
- Decr in CD71+ cells w/ postnatal develop»loss of immunosupp
- CD71+ cells quench excessive inflam induced by abrupt colonization w/ commensal microorgan after birth
Necrotizing enterocolitis in premature babies may occur due to what?
-Over-rxn to influx of bacteria since immunosuppressive CD71+ cells haven’t developed
Limits Th1 cytokines produced by microbes
TQ
From an eco pt of view, humans are a superorganisms, a communal collective of human + microbial cells working as one
-we should tail tx to both human and microbes
ex?
Fecal microbiota transplant
