The third line of defense in the immune system is specific due to the targeted response of B-cells and T-cells, which are designed to recognize and respond to specific antigens. Unlike the first line of defense (skin and barriers) and the second line (macrophages and other nonspecific immune responses), which act broadly against pathogens, the third line utilizes antibodies that bind specifically to particular antigens, akin to enzyme-substrate interactions. This specificity arises from the unique receptors on B-cells and T-cells that are tailored to identify distinct pathogens. The activation of these cells leads to the production of antibodies that are effective against specific variants of pathogens, making this response highly specialized and efficient.