DEFENDING THE BODY FROM WITHIN
The Human Immune System
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Once pathogens gain entry to the body, they face a complex immune system that is highly effective but not perfect. Two separate sets of white blood cells play starring roles in the ensuing battle — as they orchestrate, direct, and carry out a sequenced series of increasingly specific attacks against the invading microbes. |
Artist's rendering showing the immune system working against bacteria invading the lymph node.
As shown here, the first set of cells — neutrophils, monocytes (which generate the mighty macrophages), eosinophils, and basophils — serves as an instant, on-demand immunological defense system. Always on the ready, these cells wage a generalized campaign of destruction against any pathogens that might come their way while signaling other cells of the presence of intruders.
Highly simplified diagram showing the one-two punch of the immune system.
The on-the-ready cells (at left) function in multiple ways. Neutrophils "eat" pathogens and send off distress signals. Monocytes are triggered to turn into pathogen-eating macrophages. Eosinophils attack parasites, and basophils contain granules filled with histamine and other compounds related to allergies. The second set of cells — the lymphocytes — is slower to react.
As the generalized campaign goes forward, a second set of specialized cells known as lymphocytes begins a more specific and enduring attack. The stars of this more adaptive immunological defense system — killer T cells, helper T cells, and B cells — work in concert to destroy infected cells. The B cells mature into plasma cells that generate highly specific antibodies capable of producing lasting immunity. And, among other functions, the T cells coordinate the immune system response. Any material that triggers this immune response is called an antigen.
B and T cells perform more highly specialized tasks.
B cells recognize antigens and then (as plasma cells) mass-produce
highly specific antibodies. Helper T cells, in addition to other tasks,
play a central role in coordinating the attack. Killer T cells, once
activated, destroy virus-infected cells.