Elevated Levels of α2-Macroglobulin-Protease Complexes in Infants

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Abstract
Proteases form stable complexes with α2-macroglobin (α2-MG) in human plasma. We previously showed that the intestine of newborn rabbits takes up greater amounts of proteases than the intestine of weaned animals, and we suggested that the same phenomenon might occur in the human newborn. To test this possibility, α2-MG complexes were sought in plasma from 3-day-old human infants and adults. In addition, the level of α2-MG was measured. The concentration of α2-MG complexes and of α2-MG was significantly increased in the plasma of infants compared to adults. We suggest that the elevated levels of α2-MG complexes in infants may reflect the enhanced uptake of proteases from the intestine. In addition, there may also be decreased clearance of complexes by the mononuclear phagocytic system in infants. The elevated levels of α2-MG in the infant may reflect a response to the need for neutralizing proteases absorbed from the intestine.