DECREASED Ia-AG ON HUMAN NEC: NATAL MACROPHAGES (A MARKER CF MATURATION?

Abstract

Neonates are susceptible to severe viral and bacterial infections which may be due to immaturity of their immune system. Macro-phages are one of the critical elements in host defense and are important for many specific immune processes including gamma interferon production. Studies in our lab have shown that a functional immature neonatal macrophage is primarily responsible for the impaired production of PHA-induced gamma IFN by mononuclear cells of neonates (age 1-7 days). This defect improves with time of in vitro cultivation (≥3 wks) and also is age related in vivo (≥2½ mos). Neonatal mice have been shown to have a defect in antigen presenting function which is correlated with a decreased number of Ia AG bearing macros. To investigate factors associated with this macrophage defect in newborns, we studied adherent cells from Ficoll-Hypaque separated cord and adult cells in vitro for evidence of Ia AG by immunoperoxidase and monoclonal AB assay and morphological changes by scanning electron microscopy. We found that only 26% of 7 day old neonatal macros expressed Ia AG vs 90% in comparable adult macros. No gross morphological differences were seen by SEM of adult or neonatal macros at 5,6,7,8 days of age. However we found 2 populations of neonatal macros at 7 days with 10-15% large macros (diameter ≅40u) compared to 20-30u adult macros. In an attempt to activate neonatal macros we pretreated 6 day old neonatal macros for 8 hrs with Meloy interferon (.1, 1 and 10 IU) added neonatal T cells (2×10⁵/ml) and stimulated with PHA and found no enhancement of IFN production in 48 hr supernates. Further investigation into the nature and correction of this impaired function may suggest future therapeutic possibilities.

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