Biology – The immune system | e-Consult

In a primary viral infection, the initial response relies heavily on innate immunity, with macrophages playing a key role in early pathogen recognition and containment. Macrophages phagocytose the virus and present viral antigens on MHC class II molecules to helper T-cells (Th cells). This antigen presentation is critical for initiating the adaptive immune response.

Activated Th cells release cytokines that stimulate B-lymphocytes to differentiate into plasma cells. Plasma cells then produce antibodies specific to the viral antigens. These antibodies can neutralize the virus by preventing it from entering host cells, or they can opsonize the virus, making it easier for phagocytes to engulf and destroy. Antibody production is a hallmark of the humoral immune response in viral infections.

Cytotoxic T-cells (killer T-cells) are activated if they recognize viral antigens presented on MHC class I molecules on infected host cells. These killer T-cells then directly kill the infected cells, preventing viral replication and spread. This is an example of cell-mediated immunity. The interaction between Th cells and killer T-cells is essential for a coordinated and effective response to viral infection.

The primary immune response to a viral infection is relatively slow, taking several days to fully develop. However, it generates a population of memory B-cells and memory T-cells, which provide long-lasting immunity against subsequent viral infections. The initial response is crucial for controlling the viral load and preventing severe disease.