Background: Findings in studies in rodents have suggested that epithelial growth of the small intestine is dependent on activation of the immune system. The purpose of this study was to compare changes of postnatal epithelial growth with immunologic activity in humans.
Methods: Duodenal biopsies were obtained by endoscopy from 74 infants. Villus area, crypt length, and mitotic count were measured, using a microdissection technique. Enterocyte height, intraepithelial lymphocytes and mucosal mast cells were recorded in histologic sections, and soluble interleukin-2 receptor levels were measured in sera. These data were compared with those from 77 adult control subjects.
Results: Mean ± SD villus area was similar in infants compared with that in adults (0.364 ± 0.108 mm2 vs. 0.339 ± 0.1 mm2); but mean crypt length was 31% longer (270 ± 56 μm vs. 206 ± 29 μm; p < 0.0001), and mitotic count was 68% higher (4.2± 2.8 vs. 2.5 ± 1 per crypt; p < 0.0001) in infants. Enterocyte height was lower during infancy (27.0 ± 3.4 μm vs. 30.9 ± 4.6 μm; p < 0.0001). There was no evidence of a trophic effect on the small intestine of breast feeding compared with the effect of bottle feeding. Counts of intraepithelial lymphocytes but not mucosal mast cells were significantly less in infants. Mean soluble interleukin-2 receptor levels peaked during early infancy, compared with levels in adults (1,820 ± 596 U/ml vs. 695 ± 359 U/ml).
Conclusion: These results indicate that epithelial proliferation is increased during infancy at an age when immunologic activity is high.