BACKGROUND:Little data have been available concerning the mechanism of drag resistance and anti-apoptosis in leukemic cells of leukemia children.The majority of studies focus on normal bone marrow mesenchymal stem cells (MSCs) and established stroma cells,but not interaction of MSCs and leukemic cells in leukemia children.OBJECTIVE:To explore the effect of MSCs in leukemia children on the proliferation and apoptosis of leukemic cell strain K562/AO_2.DESIGN,TIME AND SETTING:In vitro cytology experiment was performed at the laboratory of Department of Pediatrics,First Affiliated Hospital of Guangzhou Medical College from December 2007 to August 2008.MATERIALS:MSCs were provided by 30 leukemia children admitted to First Affiliated Hospital of Guangzhou Medical College,including 22 acute lymphoblastic leukemia and 8 acute myeloblastic leukemia.Written informed content was obtained from all families.K562/AO_2 was provided by Tianjin Institute of Hematopathy.METHODS:MSCs were isolated and cultured by Ficoll density gradient method.They were cultured in two conditions:the co-culture of MSCs and K562/AO_2 and K562/AO_2 suspension alone.In co-culture group,1×10~8 /L K562/AO_2 cells at log phase were added to confluent MSCs,and free floating K562/AO_2 cells were discarded after 24 hours.MAIN OUTCOME MEASURES:Effect of MSCs on the growth of K562/AO_2 cells was observed;effect of addamycln on K562/AO_2 cell apoptosis was detected by AnnexinV-FITC method.Cell cycle was determined by flow cytomtry,mdrl gene of K562/AO_2 cell was detected by Taqman-MGB probe real-time PCR.RESULTS:Compared with K562/AO_2 alone,the K562/AO_2 cell co-cultured with MSCs grew slower and the log phase of growth was not significant;the rate of apoptosis in earlier period was significantly decreased (P ＜ 0.05);co-cultured K562/AO_2 G_0-G_1 phase increased,but S phase decreased.No changes in mdr1 gene in cells were found between two culture conditions (P ＞ 0.05).CONCLUSION:In vitro cytology has demonstrated that leukemia children MSCs induce drug resistance of K562/AO_2 cells by changing K562/AO2 cell cycle through adhesion to avoid pro-apoptotic effect of drugs but not related with mdr1 gene.

The web-based PBL teaching plan in pediatrics embodies the network learning environment and learning requirements.The basic design unit is a complete real case with certain width and depth,which can stimulate the students' interests of participation and guide students into a predetermined learning area to achieve desired learning objectives.The article dwelled on the compilation and implementation of the teaching plan of children bronchopneumonia.The first part:teachers showed the case in PBL site and proposed the questions.Students made the Powerpoint after studying and discussing in groups by PBL teaching website,QQ group,SMS platform,etc.The second part:students reported and discussed in groups; the teacher provided the new information and put forward the following-up problems; students consulted the documents and materials through the network again; finally teachers made comments on the results.During the teaching,network should be fully utilized and the questions should be proposed progressively at different levels.Teacher should play a guiding role and emphasize the students' autonomous learning.