What does a phagocyte presenting processed antigen to a B lymphocyte exemplify?

The process in which a phagocyte presents processed antigen to a B lymphocyte is an important aspect of the immune response that illustrates integrated defense mechanisms of the body. In this context, integrated defense refers to the coordination of different components of the immune system working together to mount an effective response against pathogens.

When a phagocyte, such as a macrophage or dendritic cell, engulfs a pathogen, it breaks it down and presents fragments of the pathogen (antigens) on its surface using molecules called major histocompatibility complex (MHC) proteins. This antigen presentation serves as a crucial link between the innate immune response (mediated by phagocytes) and the adaptive immune response (involving B and T lymphocytes). By presenting the processed antigen to a B lymphocyte, the phagocyte helps initiate the activation and proliferation of B cells, which leads to the production of antibodies specific to that antigen.

This situation exemplifies integrated defense because it highlights how the innate and adaptive components of immunity interact to create a more robust response to infection. The other choices, such as passive immunity and cell-mediated immunity, refer to different mechanisms of the immune response, while the humoral response specifically relates to the actions of antibodies produced by B