Final answer:
The second line of defense in the immune system is the cellular response, involving adaptive immunity with both humoral and cellular components. Antibodies produced by plasma cells and T cells are key players in this specialized defense against pathogens.
Step-by-step explanation:
The second line of defense for the body's immune system is the cellular response, which is part of the adaptive immunity. This specialized part of the immune system involves humoral immunity (antibodies produced by plasma cells) and cellular immunity (T cells directed against intracellular pathogens). This second line of defense comes into play if a pathogen breaches initial barriers such as the skin and mucous membranes.
Antibodies are produced primarily by plasma cells and are specifically targeted against each pathogen, which is part of the humoral immune response. Cellular adaptive immunity is carried out by T cells, which includes cytotoxic T cells that work in concert with natural killer cells against virally infected cells. In contrast to innate immunity, which is general and nonspecific, adaptive immunity adapts to specific pathogens after repeated exposure and creates immunological memory, preventing the same pathogen from causing disease repeatedly.