Immune Response Against Viral Pathogens

Upon viral infection, cells secrete interferons to protect uninfected cells and activate the patrolling NK cells to initiate a non-specific innate immune response.

These NK cells have pathogen recognition receptors that recognize diverse viral antigens on infected cells and eliminate them by cell lysis.

The lysed virus-infected cells release viral antigens that are engulfed by APCs like dendritic cells, which display them with both MHC I and MHC II.

The antigen-MHC I complex is presented to antigen-specific naive CD8 T cells, which differentiate into cytotoxic T cells to kill virus-infected cells.

In contrast, the antigen-MHC II complex activates antigen-specific CD4 T cells, giving rise to helper T cells.

These cells enhance cytotoxic T cell activity for the destruction of infected cells.

Additionally, helper T cells activate B cells, whose receptors can directly bind free viral particles, differentiating into antibody-producing plasma cells.

These secreted antibodies bind other free viral particles, preventing them from penetrating target cells and marking them for neutralization by phagocytes.