What type of lymphocyte matures in the bone marrow and secretes antibodies?

B lymphocytes, also known as B cells, are the type of lymphocyte that matures in the bone marrow and is primarily responsible for the production and secretion of antibodies. These antibodies are critical components of the immune response, as they specifically bind to antigens on pathogens such as bacteria and viruses, helping to neutralize and eliminate them from the body.

The maturation of B lymphocytes occurs in the bone marrow, which is where they undergo selection processes to ensure that they can effectively identify foreign antigens while avoiding self-reactivity. Once matured, B cells can differentiate into plasma cells, which are the effector cells that produce large volumes of antibodies.

In contrast, T lymphocytes mature in the thymus and have different roles in the immune system, such as assisting other immune cells or directly killing infected cells. Natural killer cells are a type of cytotoxic lymphocyte but do not secrete antibodies as part of their function. Helper T cells, while crucial for orchestrating the immune response, also do not produce antibodies but instead help activate B cells and other immune cells.

This understanding highlights the specific role of B lymphocytes in immunity and their unique ability to produce antibodies as opposed to the other lymphocytes mentioned.