Lymphatic System and Lymphocytes

Lymphocytes

• Lymphocytes (lymphoid cells) are leukocytes from bone marrow that defend against antigens (foreign substances like viruses, bacteria, toxins, and transplanted tissues).

• There are three types: natural killer cells, B cells, and T cells.

• Lymphocytes mature and differentiate in lymphoid tissues to become specialized antibodies.

Natural Killer (NK) Cells

• NK cells kill cancer cells and cells infected by viruses.

B Cells

• B cells (B lymphocytes) produce antibodies and are effective against viruses and bacteria in the blood.

• When a B cell encounters its specific antigen, it transforms into a plasma cell.

Plasma Cells

• Plasma cells develop from B cells and secrete antibodies to destroy specific antigens.

T Cells

• T cells (T lymphocytes) originate in the thymus and are central to cell-mediated immunity.

Cytokines

• Cytokines (e.g., interferons and interleukins) are proteins released by T cells that act as intracellular signals to initiate the immune response.

Interferons

• Interferons (IFNs) are produced in response to antigens (viruses or tumor cells).

• Interferons activate the immune system, fight viruses by slowing their multiplication, and signal other cells to increase defenses.

Interleukins

• Interleukins direct B and T cells to divide and proliferate, playing multiple roles in the immune system.