Lymphocytes respond to antigen in peripheral lymphoid organs, such as lymph nodes or spleen.

What activates a lymphocyte?

Lymphocyte activation occurs when lymphocytes (B cells or T cells) are triggered through antigen-specific receptors on their cell surface. This causes the cells to proliferate and differentiate into specialized effector lymphocytes.

Do T cells activate lymphocytes?

Helper T cells do not directly kill infected cells, as cytotoxic T cells do. Instead they help activate cytotoxic T cells and macrophages to attack infected cells, or they stimulate B cells to secrete antibodies. Helper T cells become activated by interacting with antigen-presenting cells, such as macrophages.