Objective To investigate the present situation of social practice of medical students and to analyze its influencing factors, to provide scientific basis for improving students' participation and quality of participation. Methods The survey of 374 medical students of Peking University was conducted in July 2015, using a self-made questionnaire including the cognition of social practice, social practice experience, etc. The sample of students was selected by cluster sampling from 2007 to 2014 grades. There were 370 valid questionnaires; the effective response rate was 98.8%. IBM SPSS statistics 20.0 was used to make statistical analysis and data were processed by description analysis and ordinal regression analysis. Results 328 persons (88.6%) affirmed the importance of social practice. However, 120 students (32.4%) did not take part in social practice in last school year. There were 357 students participating in social practice during the university. 341 students (95.5%) achieved and even exceeded the practice expectations. Secondly, it depicted the influence factors of students' participation in social practice, including family economic factor, former social practice experience before entering university, and the personal factors which included grade, overall rating scores points, and position. Moreover, factors influencing the quality of their participation included the preparation time of social practice, the output, the awards and the guide teacher. Conclusions It showed that the situation of medical students' participation in social practice was not satisfactory. It sug-gested schools set social practice credit requirements, and strengthen the freshmen education, to establish students' inertia effect of social practice.

The CC chemokine receptor 5 (CCR5) is a G protein-coupled receptor that regulates chemotaxis and effector functions of immune cells. It also serves as the major co-receptor for the entry of human immunodeficiency virus (HIV). Recently, CCR5 inhibitors have been developed and used for the treatment or prevention of HIV infections. Additionally, it has been identified that CCR5 controls bone homeostasis by regulating osteoclastogenesis and the communication between osteoblasts and osteoclasts. However, the effects of CCR5 inhibition on bone tissue in elderly patients are unknown. This study aimed to examine the bone phenotype of aged CCR5 knockout (KO) mice. Femoral and tibial bones were isolated from 12-month and 18-month old wild-type (WT) and CCR5 KO mice, and microcomputed tomography and histology analyses were performed. Twelve-month-old CCR5 KO mice exhibited a decreased trabecular bone mass and cortical bone thickness in both femoral and tibial bones compared with age-matched WT mice. Eighteen-month-old mice also showed a decreased trabecular bone mass in femurs compared with control WT mice, but not in tibial bones. Unlike in 12-month-old mice, the cortical margin of femurs and tibias in 18-month-old mice were rough, likely because they were aggravated by the deficiency of CCR5. Overall, our data suggest that the deficiency of CCR5 with aging can cause severe bone loss. When CCR5 inhibitors or CCR5 inactivating technologies are used in elderly patients, a preventive strategy for bone loss should be considered.