305 Flashcards
Why is the preterm infant considered a “compromised host”?
immaturity of the immune system, decreased levels of IgG and disruption of skin barriers
What organisms is the infant at risk of being colonized with from the maternal genital tract?
lactobacillus, E.choli, protective anaerobes, GBS and chlamydia
The prenatal GI tract is considered to be what?
sterile
Initial colonization of the neonate occurs where on the body?
neonatal skin, umbilical cord, genitals, eyes, throat and nares
GIT colonization occurs in what two stages?
1) at birth through contact with organism
2) through diet
How does breast milk promote a protective GIT environment?
maintains an acid environment, thereby limiting the growth of acid sensitive organisms, promotes the growth of lactobacillus and bifidobacterium and is protective against G+ and G- organisms
What sort of environment do formula fed infants have in their GIT?
formula promotes a buffer in the GIT, therefore it is a more alkaline environment, less protective
Why are probiotics given to the neonate?
It encourages the colonization with desirable flora (lactobacillus and bifidibacterium)
What are the affects of probiotics?
dec the risk for NEC, dec emesis events, inc gastric emptying time, inc number of stools, dec crying spells; no a/w inc nosocomial infx events
How is PMN fx limited in the neonate?
1) poor response to chemotaxic factors
2) impaired mobilizations (dec ability to leave vasculature)
3) decreased chemotaxis
4) decreased opsonization (r/t dec levels of immunoglobulins and complement comp)
5) decreased phagocytosis
6) decreased macrophage activity
7) low levels of natural killer cells
8) unable to inc neutrophil production
What are the most common cytokines?
Interleukin 1 and Interleukin 6
Why is the neonate unable to inc neutrophil production?
less bone marrow reserve, fewer neutrophils in the reserve pool. neutrophils that are produced are immature and with impaired fx
What is the net result of an impaired neonatal immune system?
the infant is unable to localize infx leading to generalized sepatcemia
How does stress affect the immune system?
1) dec bactriocidal activity (both G+ and G-)
2) dec phagosytosis
3) dec ability to localize infx
Why are there changes in cellular metabolism and decreased phagocytosis r/t stressed and SGA infants?
due to decreased oxygen consumption, O2 free radicals all of which compromise bacteriocdial activity
What is the only immunoglobulin to cross the placenta?
IgG
When does IgG begin to cross to the neonate?
Beginning in the 3rd mo GA and increasing until term; greatest transfer is in the last trimester
What are the most important IgGs?
IgG1 and IgG3; non specific responders via opsonization
When is IgA present in the fetus?
30wk GA; does NOT cross placenta; introduced after birth via breast milk
When is secretory IgA present in the neonate and where?
by 2-3 wk of age postnatally; present in intestinal mucosa, tear and saliva; provides local immunity
Which immunoglobulins are directly responsible for antibodies against the most common organisms causing neonatal sepsis?
IgG and IgA
When is IgE produced and what is its function?
does NOT cross placenta, production begins at 12 weeks and provides protection against allergens
When is IgG produced and what is its function?
productions begins at 12 weeks and provides protection against G- organisms and viruses
IgM is predominately secreted by what?
B lympocytes
What is the crucial role played by IgM?
fetus can produce immunoglobulin in response to TORCH infections after 19-20 wk GA; protection against blood borne pathogens
Compared to adults, what is the specificity of IgM?
less specificity
What is the major immunoglobulin synthesized in the first month of postnatal life?
IgM
Where are T lymphocytes produced?
in the thymus
What is the role of the T lymphocytes?
to recognize foreign antigens by interacting with a major histocompatibility complex antigen
Why are MHC important to T cells?
It is the only way that t cells can recognize infected cells is through MHC identification
What does the release of lymphokines achieve?
recruits macrophage, lymphocytes and phagocytes and inhibits viral replication
What is the function of helper T cells?
to release lymphokines and recruit antibodies
What is cell mediated immunity comprised of?
T cells, natural killer cells and B cells
What are the types of T cells?
helper T cells and suppressor cells
What is the function of the suppressor cells?
turn off antibody reactions
What is the function of the cytotoxic (natural killer) cells?
they are lethal to tissues invaded by viruses and destroy cancer cells and other foreign invaders
What is the function of the lymphokines?
activate helper T cells and are endogenous pyrogens
Why are neonates at increased risk for infections?
1) dec fx ability of T lymphocytes
2) immature T lymphocyte receptors
3) lymphokine production reduced
4) suppressor cell activity is dormant
5) dec cytotoxic activity
6) dec number of T cells
When do T cells appear in the neonate?
do NOT cross the placenta; immunity can take 4-6 weeks postnatally to develop
What is the function of the complement system?
1) back up to immunoglobulins
2) attach antibody “tail” after contact with antigen
3) proteins connect in a cascade and attach antigen destroying it
4) assists with inflammation and opsonization
What is the state of the complement system of the neonate?
few protein components (in term infant, levels are 50-75% that of an adult; 28wk GA infant they are 10-30%)
What is the result of an impaired complement system?
decreased opsonization, decreased chemotatic activity and decreased cell lysis
What are common G+ cocci in neonates?
Strep A, B, D pneumoniae, staph, staph a, staph epi
What are common G- cocci in neonates?
Neisseria, Neisseria meningitidis, Neisseria gonorrhoeae
What are common G+ rods in neonates?
Listeria, diphtheriae, clostridium, c.diff, c. tetani, corynebacterium
What are common G- rods in neonates?
enterobacteriaceae, E.coli, Klebsiella, Shigella, Proteus, Salmonella, H influenza, Psesudomonas
What is the antibiotic of choice for staph aureus?
cephalosporin+ methicillin/ vanc/ clindamycin
What is the antibiotic of choice for strep a & B?
Penicillin G or amp
What is the antibiotic of choice for pseudomonas?
gent + ticarcillin
By 1 year of age, total immunoglobulin levels are what precent of adult values?
60%
What are the levels of IgG postnatally?
significant inc in first 6 months, adult levels by 5-6 years
What are the levels of IgA postnatally?
20% of adult levels at 1 year of age, complete levels by adolesence
What are the levels of IgM postnatally?
50% of adult levels by 6 months, 75-80% adult levels by 1 year
What are the levels of complement postnatally?
increased to adult levels by 6-12 months
When is T cell function mature?
by 3-6 mos
When does an infant’s risk of infection decrease?
after 2-3 months of age
What is the level of function of a neutrophil postnatally?
chemotaxic ability is decreased until 2 years of age, monocyte chemotaxis decreased until 6-12mo
