What characterizes the third line of defense in the immune system?

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The third line of defense in the immune system is characterized by a specific response with immunological memory. This level of defense engages the adaptive immune system, which is tailored to recognize and combat specific pathogens that the body has encountered previously. Unlike the innate immune response, which is immediate and non-specific, the adaptive immune response involves the activation of lymphocytes, such as B cells and T cells.

B cells are responsible for producing antibodies that specifically target antigens on pathogens, while T cells can directly kill infected cells or help regulate other immune responses. One of the key features of the third line of defense is its ability to remember past infections; if the same pathogen invades again, the immune system can mount a faster and more effective response, owing to the memory cells that remain after the initial exposure. This specificity and memory make the adaptive immune response critical for long-term immunity and the effectiveness of vaccines.

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