The inflammatory response stimulates neutrophils and macrophages to migrate to a site of infection. This animation can be used to demonstrate to students the microorganism–macrophage interaction that leads to antibody synthesis and immune memory.

The macrophage phagocytizes the microorganism, killing it and breaking its macromolecules into fragments. These fragments, in conjunction with the major histocompatibility complex type II (MHC II), are displayed on the macrophage cell surface. This presentation triggers CD4+ T-helper lymphocytes to combine with the presented antigen and activate antibody synthesis by differentiated B-cells called plasma cells. Instead of differentiating into plasma cells, other B lymphocytes remain committed and ready for the next contact with this specific antigen.

Macrophages and T-helper cells release, and are activated by, secreted products called cytokines. Cytokines are small proteins that serve a variety of functions and include interleukins, interferons, colony stimulating factors, tumor necrosis factors, and growth factors. Some cytokines positively regulate the immune response by stimulating growth and maturation of target cells; other cytokines negatively regulate the immune response through a series of inhibition reactions.