Abstract: Objectives To investigate the expression and the clinical significance of costimulatory molecules 4-1BB and 4-1BBL in the peripheral blood mononuclear cell of children with Henoch-Schönlein purpura nephritis (HSPN). Methods Twenty children with incipient HSP were included as one group, 20 children with incipient HSPN as another group (15cases of them with renal pathologic examination), and 20 healthy children as the normal control group. RT-PCR was used to detect the change of 4-1BB/4-1BBLmRNA in PBMC, and to analyze the relationship between the change of 4-1BB/ 4-1BBLmRNA in PBMC of the HSPN group and the pathology of the kidney. Results The expression of 4-1BBmRNA, 4-1BBLmRNA in children with HSPN and HSP  were significantly higher than that of the normal control group (P