Immune system

The immune system is the network of organs and processes that protects the body from infectious agents and disease. It includes T-cells and B-cells, named for their respective origin organs, the lymph system, and the integumentary system (hair and skin)

Leukocytes
Leukocytes are white blood cells, a category that includes lymphocytes, macrophages, neutrophils, eosinophils, and basophils.

Macrophages literally consume pathogens in a process called phagocytosis. After detecting a bacterium, the macrophage (or any phagocyte in general) attaches to it by a receptor on its surface and engulfs the target. Then, its lysosomes digest the bacterium. Afterwards, the macrophage displays the bacterium's antigen, a structure on the bacterium that identifies it as a foriegn body.

Lymphocytes can be divided into T-cells, B-cells, and natural killer cells. Naturaly killer cells are not covered in the cell unit of Grade 11 IB biology.

T-cells are named for their specialization within the thymus. All lymphocytes are original produced in the bone marrow, but T-cells travel to the thymus to mature. T-cells mainly exist as helper or killer cells. Helper T-cells, also known as CD4 T-cells, oversee intercellular communication and coordinate the immune response by means of cytokines, which are just chemicals that cells use to communicate. CD4 T-cells also help B-cells become plasma or memory cells

Killer, or cytotoxic CD8 T-cells, seek out and destroy cancerous, infected, or otherwise compromised cells. They kill targeted cells by destroying the cell membrane or inducing programmed cell death.

B-cells originate from the bone marrow, although they were originally named for something else. They remain dormant until activated by a helper T-cell, at which point they become plasma cells to produce antibodies or become memory B-cells that retain certain information about an antigen so future responses will be swifter and more effective.