Objective      To study genesis of lymphoid tissue and distribution

localization and development of IgM-positive B cells in human fetal ileum.     Methods      Human fetus specimens from terminated pregnancies

12 males and 18 females with gestational ages of 9-28 weeks

were collected from hospitals in Guiyang

China

between Jan. 2003 and Dec. 2005. All pregnant women were informed of the purpose of this study and the protocol was approved by the Ethics Committee of Guiyang Medical College. HE staining was adopted to observe

the genesis of lymphoid tissue in human fetal ileum. IgM-positive B cells were detected by immunohistochemical SABC staining

and counted by BioMias 29 image analysis software. Relevant data were statistically analyzed.     Results      In the ilea of 9-week fetus specimens

a small amount of lymphocytes were observed in the mesenchyme out of epithelia

part of which expressed membrane IgM. In the ilea of 17-week fetus specimens

lamina propria lymphocytes aggregated to form solitary lymphoid nodules with an increased amount of IgM-positive B cells. In the ilea of 24-week and older fetus specimens

typical Peyer’s patches could be observed. IgM-positive B cells existed mainly in lymphoid nodules and sporadically in lamina propria connective tissue or chorionic epithelium. Cell counting results showed that IgM-positive B cells in human fetal ilea increased from 12.80±5.72 in 9-12 week to 201.30±36.35 in 25-28 week with statistically significant difference (

P

<

0.05).     Conclusion      Lymphoid tissue of human fetal ileum wall is nearly mature at 24 weeks old. Human fetal ileum can potentially synthesize and release IgM that is important for constructing and improving fetus intestinal immunity.