The hepatitis B virus (HBV) is predominantly a hepatotropic virus but also infects cells of the lymphatic system. HBV genomes (DNA, messenger (m)RNA, covalently closed circular (ccc) DNA) and proteins have been found in extrahepatic sites such as peripheral blood mononuclear cells (PBMC), lymph nodes, spleen, bone marrow and cerebrospinal fluid. HBV entry into hepatocytes occurs by binding of the HBV preS1 surface protein to its specific receptor, the bile acid transporter, sodium taurocholate co-transporting polypeptide (NTCP). Although the mechanism of HBV entry into lymphatic cells is unknown, the pre S1 encoded surface protein is thought to be involved. Extrahepatic HBV infection has been studied in both chronic HBV (CHB) and in occult HBV infection (OBI). Studies have shown that HBV genomes are present in different PBMC subsets from chronically infected carriers. Unique HBV variants have been found in PBMC compared to plasma or liver in both nucleos(t)ide analogue (NA) treated and untreated CHB carriers, suggesting replication and compartment specific evolution of HBV. In HBV coinfection, HBV genomes were found in PBMC from hepatitis C virus (HCV), human immunodeficiency virus (HIV) and hepatitis delta virus (HDV) co-infected individuals. Moreover, during pregnancy, the trans placental passage of HBV infected PBMC from highly viremic mothers to infants is one of the postulated means of vertical transmission of HBV. Taken together, HBV infection in extrahepatic sites (i.e., PBMC) is implicated in multiple facets of HBV pathogenesis such as persistence, viral evolution and vertical transmission.

乙型肝炎病毒（HBV）主要是肝炎病毒，但也会感染淋巴系统细胞。HBV基因组（DNA，信使（m）RNA，共价闭合环状（ccc）DNA）和蛋白质已在肝外部位发现，例如外周血单核细胞（PBMC），淋巴结，脾脏，骨髓和脑脊液。HBV进入肝细胞是通过HBV preS1表面蛋白与其特异性受体，胆汁酸转运蛋白，牛磺胆酸钠共转运多肽（NTCP）结合而发生的。尽管尚不清楚HBV进入淋巴细胞的机制，但据认为与S1编码的前表面蛋白有关。在慢性HBV（CHB）和隐匿性HBV感染（OBI）中都已经研究了肝外HBV感染。研究表明，HBV基因组存在于慢性感染携带者的不同PBMC亚群中。在经核苷酸（t）化物类似物（NA）处理和未处理的CHB载体中，与血浆或肝脏相比，在PBMC中发现了独特的HBV变体，表明HBV的复制和部分特异性进化。在HBV合并感染中，在PBMC中发现丙型肝炎病毒（HCV），人免疫缺陷病毒（HIV）和丙型肝炎三角洲病毒（HDV）共同感染的人的HBV基因组。此外，在怀孕期间，HBV感染的PBMC从高度病毒血症的母亲到婴儿的经胎盘传代是HBV垂直传播的假定手段之一。总体而言，肝外部位（即PBMC）的HBV感染与HBV发病机制的多个方面有关，例如持续性，病毒进化和垂直传播。