Final answer:
The antibody and cell-mediated immune responses become activated in a few days in immunocompetent individuals during a first exposure to a pathogen. Memory cells result in a much faster response upon secondary exposure. The adaptive immune response, involving antibodies and T cells, is specific to the pathogen and takes days or weeks to become fully activated.
Step-by-step explanation:
Antibody and cell-mediated responses to an infectious agent become activated in a few days in immunocompetent individuals. This period is necessary for the steps of the primary immune response, which includes the activation and proliferation of B and T cells specific to the antigen. In the case of a second infection by the same pathogen, the response is much faster due to the presence of memory cells, which can provide immunity within a few hours or days, preventing the disease from emerging.
During a first exposure to a novel pathogen, the initial immune response includes phagocytosis by phagocytic cells as part of the innate immune system. If this is not sufficient, the adaptive immune response is activated, which is specific to the invading pathogen and includes antibodies and T cells. The adaptive immune response takes significantly longer to become established compared to the innate response.