How different are the actions of antibodies against bacteria and against virus? Why is the cellular immune response activated in case of chronic viral infection?
The antibodies of the humoral immune system act against extracellular agents, such as toxins or bacteria, but they are not active in the intracellular space and they cannot fight virus efficiently.
In case of viral infection (and also of cancerous or precancerous cells) the immune attack is made by the cellular immune system, mediated by T and NK (natural killers) lymphocytes that destroy exact cells and virus.