The thymus makes T cells. The bone marrow is the origin of B Cells. They flow in the tunnels and vessels that make up the lymphatic system and congregate in lymph nodes and lymphatic tissue. These are like command centers, surveillance hubs where the firefighters are awaiting a call. The T cells, when alerted by dendritic cells, behave as soldiers and generals, spitting out cytokines; the B cells use antibodies to connect to antigens as if they are keys in search of a lock. Macrophages, neutrophils, and natural killer cells roam the body, tasting and exploring, killing. These networks get
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