Victor,
First, lets separate the humoral from the cell mediated immune
responses. For the generation of CMI responses against viruses, most
infected cell will present viral peptides via MHC-I proteins, so the
virus doesn't need to infect a professional APC. Most nucleated cells
constantly present self-proteins via MHC-I, allowing for immune
surveillance. For humoral immune responses, the virus can be
presented by APCs following phagocytosis, without the need for actual
infection (replication) of the APC. In addition, when CTLs lyse
virally infected cells, viral proteins are released which can be taken
up and processed by APCs such as macrophages and B cells for a humoral
immune response.
Jay Mone'
