Table 1.
Summary of differences in development between preterm infant, term infant and adult immune components.
| Preterm infant | Full term infant | Adult | |
|---|---|---|---|
| Skin epithelium | Thin epidermis | More developed | Normal |
| No lipid layer | Lipid layer present | Normal | |
| Neutral pH | Acidic pH | Acidic pH | |
| Vernix caseosa develops late | Vernix caseosa present | Not present | |
| – | Broad array of AMPs | Less AMP diversity | |
| Keratinocytes underdeveloped | Commensal bacteria interact with keratinocytes to make AMPs | – | |
| Gut epithelium | Higher levels of PRR expressed on epithelial cells | Fewer PRR | Normal levels |
| Few Paneth cells; decreased AMPs | Paneth cells make lysozyme and AMPs | Paneth cells make lysozyme and AMPs | |
| Epithelium more permeable to pathogenic bacteria | Epithelium more resistant to pathogenic bacteria | Normal | |
| Complement | Low levels | Increased levels | High levels |
| High level C5a fragment | Lower levels | Low levels | |
| MBL | Low 5% | 10% | 100% |
| APPs | Low soluble APP | Increased | High |
| Monocytes | Comparable levels | Comparable levels | Comparable levels |
| Cannot be recruited to tissue | Recruited to tissues, but fewer tissue macrophages than adult | Normal | |
| Poor phagocytic ability | Normal phagocytic ability | Normal | |
| Low receptor levels | Normal receptor levels | Normal levels | |
| Trigger Th17 response | Trigger Th17 response | Th1 response | |
| Metabolic state | Low O2 tension | Low O2 tension | Normal O2 tension |
| Proinflammatory cytokines | Proinflammatory cytokines | No cytokine stress response | |
| High adenosine levels → Immunomodulation | Lower adenosine levels | – | |
| Dendritic cells | – | High plasmacytoid DC (pDC:cDC ratio 3:1) in serum | High conventional DC (pDC:cDC ratio 1:3) in serum |
| Low receptor levels | Low receptor levels | Normal | |
| Impaired vaccine response | Impaired vaccine response | Normal response | |
| Very low levels in tissues | Low levels in tissues | Higher levels in tissues | |
| Induce anti-inflammatory IL-10 | Induce IL-10, IL-6, and IL-23 | Induce IL1β and TNFα | |
| Poor antiviral response | Improved antiviral response | Intact antiviral response | |
| Poor induction of Foxp3(+) Treg | Poor induction of Foxp3(+) Treg | Normal induction of Foxp3(+) Treg | |
| Increased allergy prevalence | Increased allergy prevalence | ||
| Neutrophils | Very low levels of L-selectin | Low levels of L-selectin <50% | Normal |
| Low β2 integrin | Low β2 integrin | Normal | |
| Unable to diapedese | Poor diapedesis | Normal | |
| Diminished opsonization | Improved opsonization | Normal | |
| Impaired respiratory burst | Intact respiratory burst | Normal | |
| Very low levels of bactericidal molecules in neutrophilic granules | Low levels of bactericidal molecules in neutrophilic granules | Normal | |
| Poor NET formation | Poor NET formation | Normal | |
| No reserve in the setting of infection | No reserve in the setting of infection | Normal | |
| MDSC | Low | High | Low |
| NK cells | Normal to slightly higher number | Normal to slightly higher number | Normal |
| Deficient in IFNγ and TNFα production | Deficient in IFNγ and TNFα production | Normal | |
| About 50% do not express CD56; reduced cytotoxic function | About 50% do not express CD56; reduced cytotoxic function | Normal | |
| Unknown | 50% ADCC compared to adults | Normal | |
| T cells | 50% lymphopenia compared to full term | Higher counts | Normal |
| Low CD8 count, but CD8 cytolytic activity intact | Normal counts; Intact CD8 activity | Normal | |
| Impaired Th1 differentiation, favor Th2 and Th17 | Impaired Th1 differentiation, favor Th2 | Th1 differentiation intact | |
| Normal Treg levels | Normal Treg levels | Normal Treg levels | |
| Impaired homing of T cells to target tissues | – | Normal homing capacity | |
| Serum Maternal IgG | 10–50% of maternal levels | 20–30% above maternal levels | – |
| Low opsonic activity | Low opsonic activity | Normal | |
| sIgA | Low in Serum | Higher in serum | – |
| High in Mother's breastmilk | Lower in mothers breastmilk | – |