What typically triggers an adaptive immune response?

The adaptive immune response is primarily triggered by the presence of specific antigens. Antigens are unique molecules found on the surface of pathogens such as viruses and bacteria, as well as on other foreign substances. When these antigens are recognized by the immune system, they activate specific lymphocytes—T cells and B cells—that target these invaders.

This recognition is highly specific; each lymphocyte has receptors that are designed to bind to particular antigens. Once an antigen is detected, the adaptive immune system initiates a tailored response, including the production of antibodies by B cells that can neutralize pathogens, and the activation of T cells that can destroy infected cells or help coordinate the overall immune response.

The other options, while related to immune function, do not directly trigger the adaptive immune response. General inflammation is a response of the innate immune system and can occur without the presence of specific antigens. Cytokines are signaling molecules that can facilitate communication between cells and influence immune responses, but they are not the initial trigger of the adaptive response itself. The depletion of immune cells would hinder the immune response rather than trigger it. Therefore, the correct answer emphasizes the importance of specific antigens in activating the adaptive immune response.