Leucocyte

Leucocytes
Leucocytes (white blood cells) are the immune system's primary cells and are located throughout the body. There are two lymphoid tissue types:

Primary Lymphoid tissues, comprising the bone marrow and thymus where leucocytes are synthesized

Secondary lymphoid tissues, comprising the spleen, lymph nodes and mucosa associated lymphoid tissues (MALT)

Secondary lymphoid tissues contain the mature leucocytes that react to infection, triggering an immune response.

There are multiple forms of leucocyte.