Final answer:
CD8+ cytotoxic T cells predominantly respond to intracellular pathogens, such as viruses, by recognizing antigens presented on MHC class I molecules and destroying the infected cells to stop the virus from spreading.
Step-by-step explanation:
A CDB cytotoxic T cell, or more accurately a CD8+ cytotoxic T cell, is most likely to respond to or be activated by viruses. This type of T cell recognizes and responds to intracellular pathogens, like viruses, that replicate within the host's cells. Antigens from these pathogens are presented on Major Histocompatibility Complex (MHC) class I molecules. CD8+ T cells are equipped to recognize these antigens and proceed to kill the infected cells, thereby preventing the spread of the virus.
Conversely, allergens, extracellular bacteria, and intestinal helminths are typically targeted by other immune response mechanisms, like antibodies produced in the humoral immune response or various cells that interact with MHC class II molecules.