The Immune SystemThe key primary lymphoid organs of the immune system

are thymus and bone marrowSecondary lymphatic tissues such as spleen, tonsils, lymph

vessels, lymph nodes, adenoids, and skin.

Macrophage•Macrophage: A type of white blood

that ingests (takes in) foreign material. Macrophages are key players in the immune response to foreign invaders

such as infectious microorganisms .•Macrophages help destroy bacteria,

protozoa, and tumor cells. They also release substances that stimulate

other cells of the immune system .•And they are involved in antigen

presentation. To do this, they carry the antigen on their surface and present it

to a T cells.

Neutrophis and macrophages (phagocytes)

Engulf (phagocytose) and destroy micro-organisms

Eosinophils

Secrete factors which kill protozoa and worms

Natural killer cells

•Can lyse and kill cancer and virus infected body cells

•They do not engulf the cells but inject chemicals called perforins that open up channels and disintegrate the nucleus.

Langerhans cells

Langerhans cells are dendritic cells in the skin. Skin is an important barrier to infection and it has been generally assumed that the Langerhans cells only serve to warn the immune system of skin

pathogens .

Dendritic cell•There are two cell types with similar

names but different functions. Cells of the dendritic cell (DC) lineage are bone marrow derived. In the skin they are

known as Langerhans Cells (LC).

• These cells efficiently process antigen but cannot present it to T cells. LC have been shown to pick up antigen in skin and carry it via afferent lymphatic vessels to lymph nodes. Dendritic cells in lymph are known as "veiled" cells. In lymph nodes the cells, now known as tissue dendritic cells or interdigitating cells, may efficiently present antigen if they encounter the right T cell. In fact these are the best APC...............far fewer DC are required to initiate an immune

response than any other APC .

Mast cells (concentrated under the body surfaces)

Release factors which increase blood flow and vascular permeability bringing components of immunity to the

site of infection