Fetal and Infant Immune System

Fetal Immunity

Passive Immunity

  • (passage of maternal antibody -IgG only)
  • Active Immunity
  • Beginning at 8 weeks gestational age (GA)
  • IgG levels correlate with GA:
  • low until 20 weeks
  • by 40 weeks, it doubles that of 32 wks

Active Immunity

  • B cells and T cells present by 14 weeks’ GA.
  • Relatively sterile environment in utero.
  • There is an enormous unchallenged capacity.

Neonatal and Infant Immunity

Birth

  • Instant challenge.
  • Within hours, GI tract heavily colonized.

Passive Immunity (maternally acquired antibodies)

  • Circulating placental IgG lasts 6 months or longer.
  • Secretory IgA in breast milk and colostrum

Active Immunity

  • B cell responses are good.
  • Until two years of age, children do not respond well to T cell-independent antigens (i.e., polysaccharides)
  • Full T cell subsets.
  • Infants respond well to T cell-dependent antigens (i.e., proteins).
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