Final answer:
NK cells are the second type of cytotoxic lymphocyte but are a part of the innate immune system, while cytotoxic T lymphocytes belong to T cells and are part of the adaptive immune response.
Step-by-step explanation:
The second type of cytotoxic lymphocyte (CTLs) besides cytotoxic T cells are natural killer (NK) cells. NK cells are part of the innate immune response and possess the ability to destroy cells that may be infected with viruses or have turned into cancer cells, without the need for antigen presentation that cytotoxic T cells require. There are three main types of lymphocytes within the immune system: T cells, B cells, and natural killer cells. It is the T cells that include the subgroup known as cytotoxic T lymphocytes (CTLs), which play a pivotal role in the adaptive immune response by identifying and destroying infected cells before pathogens can replicate and spread.