Hepatitis B may cause an acute viral hepatitis; however, acute infection is often asymptomatic, paicularly when acquired at bih. Many individuals with chronic hepatitis B are also asymptomatic. The risk of progression to chronic liver disease depends on the source and timing of infection . Veical transmission from mother to child in the perinatal period is the most common cause of infection worldwide and carries the highest risk of ongoing chronic infection. In this setting, adaptive immune responses to HBV may be absent initially, with apparent immunological tolerance. Several mechanisms contribute towards this: Firstly, the introduction of antigen in the neonatal period is tolerogenic. Secondly, the presentation of such antigen within the liver, as described above, promotes tolerance; this is paicularly evident in the absence of a significant innate or inflammatory response. Finally, very high loads of antigen may lead to so-called 'exhaustion' of cellular immune responses. The state of tolerance is not permanent, however, and may be reversed as a result of therapy, or through spontaneous changes in innate responses, such as interferon alpha (IFN-a) and NK cells, accompanied by host-mediated immunopathology. Chronic hepatitis can lead to cirrhosis or hepatocellular carcinoma, usually after decades of infection . Chronic HBV infection is a dynamic process that can be divided into five phases ; these are not necessarily sequential, however, and not all patients will go through all phases. It is impoant to remember that the virus is not directly cytotoxic to cells; rather, it is an immune response to viral antigens displayed on infected hepatocytes that initiates liver injury. This explains why there may be very high levels of viral replication but little hepatocellular damage during the 'immune-tolerant' phase. Hepatitis B core antigen Hepatitis B core antigen (HBcAg) is not found in the blood, but antibody to it (anti-HBc) appears early in the illness and rapidly reaches a high titre, which subsides gradually but then persists. Anti-HBc is initially of IgM type, with IgG antibody appearing later. Anti-HBc (IgM) can sometimes reveal an acute HBV infection when the HBsAg has disappeared and before anti-HBs has developed Ref Davidson edition23rd pg 874