Immune cells, actors of innate and adaptive immunity. When a micro-organism or microbe (virus, bacteria) penetrates the body's barriers (skin, mucous membranes), this invasion of foreign bodies triggers the immune system's defenses. At first, innate immunity (on the left of the drawing) acts immediately. This first immune reaction stops the progression and development of microbes in the body. Macrophages, dendritic cells and neutrophils are players in innate immunity. Macrophages (in bluish green) destroy microbes by phagocytosis and produce cytokines. These cytokines call on neutrophils (among other things) to also fight against microbes. But these cytokines also drive macrophages and dendritic cells to the lymph nodes (white arrows). If despite everything, the microbes proliferate and spread in the body, adaptive immunity comes into play (on the right of the drawing). Dendritic cells and macrophages present microbe antigens to B (blue) and T (purple) lymphocytes. There are 4 kinds of