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The vertebrate immune response is divided into two broad lines of defense. First, barriers (e.g., skin and mucosal membranes) and internal defenses (e.g., inflammation and phagocytic cells) provide a quick but non-specific defense.

Second, the humoral and cell-mediated responses, both of which provide a slower but more targeted response to specific traits presented by a range of pathogens, operate by recognizing and binding to a vast array of specific foreign receptor molecules.

The hallmark feature of the specific immune response is its ability to maintain dynamic homeostasis in the face of natural or artificial agents that disrupt this balance.

By Fred the Oyster. The Immune System (pdf), Public Domain,

The feedback mechanism that governs this system is best characterized as


positive feedback because an increase in the number of antibodies in the blood will attach to foreign agents and eliminate them from the body.


positive because cytokines activate a greater number of B (plasma) cells that, in turn, will attract and activate more T- and B-cells.


negative feedback because the total quantity of antigen-complexes is removed by the liver and spleen.


negative feedback because the total number of T-cells required to overcome this infection will decrease during the immune response.

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