<p><b>OBJECTIVE</b>To investigate the effect of retinoic acid on the differentiation and maturation of B cells from lymph node of children, and relational changes of the expression levels of retinoic acid receptor genes.</p><p><b>METHODS</b>Twenty-four patients with digestive tract malformation underwent surgical operation in the surgical ward of our hospital. They were divided into 3 groups according to age: < 1 yr, 1 - 3 yr, -5 yr, 8 cases in each age group. The lymph nodes in the margin of excised tissues were obtained. The cells separated from lymph nodes were cultured in vitro. The cells were divided into 5 groups: Retinoic acid (RA), RA plus Ro41-5253, RA receptor antagonist (RA+Ro), lipopolysaccharide (LPS), lipopolysaccharide plus RA (LPS+RA) and control, and were subjected to the corresponding treatments. After 24 h and 48 h of cell culture, the surface markers on the B cells were detected by flow cytometer to observe the maturation and activation of B cells. The expression levels of retinoic acid receptor genes were quantitatively analyzed by RT- fluorescent quantitative PCR.</p><p><b>RESULTS</b>After culture, in < 1 yr group, the number of the mature B cells (IgM(+)IgD(+)CD25(-)) in the RA group was significantly higher than that in the control (24 h: 23% +/- 5% vs. 17% +/- 3%; 48 h: 28% +/- 6% vs. 22% +/- 4%) (P < 0.05), and that in the RA + RO group was not significantly different from that in the control (24 h: 16% +/- 4%; 48 h: 20% +/- 9%) (P > 0.05). The number of activated B cells (IgM(+)CD25(+)) in the LPS + RA group was obviously higher than that in the LPS group (24 h: 82% +/- 10% vs. 76% +/- 8%; 48 h: 83% +/- 8% vs. 78% +/- 10%)(P < 0.05). The level of RARalpha gene expression of B cells (lg copies/50 ng RNA) in the RA group was significantly higher than that in the control (24 h: 7.03 +/- 1.36 vs. 5.79 +/- 2.05; 48 h: 7.91 +/- 1.60 vs. 6.21 +/- 1.88) (P < 0.05), and that in the LPS + RA group was significantly higher than that in the LPS group (24 h: 7.29 +/- 1.53 vs. 5.98 +/- 1.48; 48 h: 7.83 +/- 1.66 vs. 5.79 +/- 2.36)(P < 0.05). In 1 - 3 yr group the changes of maturation and activation of B cells in the lymph nodes were the same as the < 1 yr group. In -5 yr group, such changes were not significant.</p><p><b>CONCLUSION</b>RA can promote the development of B cell from lymph node in vitro culture in <or= 3 yr children, which may be an important mechanism of vitamin A reinforcing the anti-infective immunity in young children. The expression and regulation of retinoic acid receptor genes may take part in the ontogenesis of B cell, and play a key role in the regulation of retinoic acid.</p>