This is an Open Access article licensed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unported license (CC BY-NC) (www.karger.com/OA-license), applicable to the online version of the article only. Distribution permitted for non-commercial purposes only. Abstract Background: CD40 is an important costimulatory molecule in both celluar and humoral immune responses, involved in the pathogenic processes of chronic inflammatory diseases. Few studies were performed on the

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... ation of CD40 single nucleotide polymorphism (SNP) with chronic hepatitis B virus (HBV) infection. In this study, we studied whether the CD40-1C/T polymorphism had any effect on the progression of chronic HBV infection in Chinese population. Methods: CD40 -1C/T polymorphism in the 5′-untranslated region was analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 453 chronic HBV carriers, who were divided into asymptomatic HBV carriers (ASC), moderate chronic hepatitis B group (MCHB) and severe chronic hepatitis B group (SCHB). 202 healthy individuals in the same region were enrolled in this study as the controls. The CD40 expression on B lymphocytes was detected by flow cytometry. The concentrations of soluble CD40 (sCD40) in sera were assayed by a commercial ELISA kit. Results: Our results showed the frequencies of TT genotype and T allele of CD40-1C/T polymorphism were higher significantly in ASC than those in controls (P< 0.05), while this result was not found in either MCHB or SCHB. On the surface of B lymphocytes, the CD40 expression levels in the individuals with TT genotype were significantly lower than those with CC and CT genotypes in either ASC group or healthy controls (P<0.001). The sCD40 levels in the sera of ASC, MCHB and SCHB groups were significantly higher than the controls (P<0.001). Conclusions: The CD40 -1C/T polymorphism may contribute to the susceptibility of asymptomatic HBV carriers through its effect on cell-surface CD40 expression, which indicated CD40 signaling was involved in immune tolerance of chronic HBV infection. X. Jin, J. Tang and J. Fei contributed equally to this paper.