Which cell is the principal source of interleukin 2?

• A. B cell
• B. T cell
• C. Monocyte
• D. Plasma cell

Answer: (B)

Interleukin-2 is produced mainly by activated T lymphocytes. When a T cell recognizes an antigen with proper co-stimulation, it becomes activated and releases IL-2, which acts in an autocrine and paracrine manner to drive its own proliferation and differentiation into effector and memory T cells. The IL-2 receptor is upregulated on these activated T cells (especially the CD25 component), making them highly responsive to IL-2 and reinforcing their clonal expansion. Other cell types such as B cells, monocytes, and plasma cells don’t serve as the primary source of IL-2; they focus on producing other cytokines or antibodies. So, the T cell is the best answer.