ABSTRACT
Pandemic influenza occurs when antigenic shift generates a virus to which humans are susceptible but lack protective antibodies. Many cells in the immune system have cell membrane receptors that capture immunoglobulins by their Fc region. Adaptive immunity responds to infections with extracellular pathogens by producing high affinity largely Immunoglobulin G antibodies directed against surface antigens of the pathogen. In order to initiate an adaptive immune response a naive thymus-derived lymphocyte must enter into a receptor–ligand interaction, which is termed a cognate interaction, with a licenced dendritic cell (DC) in the T-cell area of secondary lymphoid tissue. This interaction is required to elevate a naive T cell to effector/memory status. There are three types of professional antigen-presenting cells: the DC, the bone-marrow-derived lymphocyte lymphocyte and the macrophage. Viruses are obligate intracellular pathogens, and herpesviruses, in particular, are adept at subverting every step in the cytosolic antigen-processing pathway.
