Which type of cells are categorized as thymus-dependent?

T cells are classified as thymus-dependent cells because they originate from progenitor cells in the bone marrow but undergo maturation in the thymus. This maturation process is crucial for their development into functioning immune cells capable of recognizing specific antigens. Once they leave the thymus, these cells circulate throughout the body, playing a vital role in the adaptive immune response by recognizing and responding to antigens presented by other cells.

The thymus is essential for the development of various subsets of T cells, including helper T cells and cytotoxic T cells, which require specific selection processes in the thymus to ensure that they can effectively recognize foreign antigens while maintaining self-tolerance. This dependence on the thymus for maturation is what categorizes T cells specifically as thymus-dependent.

In contrast, B cells, while also a part of the adaptive immune system, mature in the bone marrow and are not dependent on the thymus. Macrophages are derived from monocytes and are important for innate immunity but do not undergo thymic development. Natural killer cells are part of the innate immune system and do not require the thymus for maturation either. Thus, T cells are distinctly categorized as thymus-dependent due to their unique development pathway.