Is adaptive immunity provided only by lymphocytes that secrete antibodies?

No, adaptive immunity is not provided only by lymphocytes that secrete antibodies. While B lymphocytes (B cells) are responsible for antibody production, there are other types of lymphocytes involved in adaptive immunity. T lymphocytes (T cells) play critical roles in cell-mediated immunity, which involves direct recognition and destruction of infected cells or foreign pathogens by cytotoxic T cells and helper T cells that coordinate immune responses. Additionally, natural killer (NK) cells, which are not lymphocytes but part of the innate immune system, can also provide adaptive-like responses through their ability to recognize and kill infected cells or tumor cells. Therefore, adaptive immunity is not solely dependent on antibody-secreting lymphocytes, but rather involves the cooperative actions of different immune cell types.