The distribution of immunoreactive interferon-alpha in formalin-fixed paraffin-embedded normal human foetal and infant tissues

Human foetal and infant tissues were studied to test the hypothesis that microbes have a role in switching on interferon-alpha (IFN-alpha) synthesis. Foetal tissues were essentially 'germ free', while the infants had been exposed to a normal microbial environment in life. IFN-alpha was first seen at 9 weeks gestation in macrophages in the liver and thereafter was seen in macrophages in most other organs. When infant lungs were compared with foetal lungs, a statistically significant increase in the number of macrophages and the percentage of these cells expressing IFN-alpha was noted in the infant lungs. No such change was observed in spleen, liver and thymus following birth. These findings suggest that there is a basal production of IFN-alpha by macrophages that is not dependent on microbial products, but that such products can enhance synthesis of this cytokine.