Function. Mechanical contractors are the professionals responsible for the installation of plumbing, heating, cooling, air-conditioning, refrigeration and ventilation systems.efore beginning a job, a mechanical contractor estimates in writing how long it will take to complete a particular job and how much it will cost, and then must complete all required work according to that schedule and in that price range.
In mammals, B cells mature in the bone marrow, which is at the core of most bones. In birds, B cells mature in the bursa of Fabricius, a lymphoid organ. (The B from B cells comes from the name of this organ, where it was first discovered by Chang and Glick, and not from bone marrow as commonly believed). B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors (BCRs) on their cell membrane.
B-Lymphocytes (B-Cells). A type of white blood cell that makes antibodies. B lymphocytes are part of the immune system and develop from stem cells in the bone marrow. Also called B cell.acrophages. A type of white blood cell that surrounds and kills microorganisms, removes dead cells, and stimulates the action of other immune system cells. Monocytes. A type of immune cell that is made in the bone marrow and travels through the blood to tissues in the body where it becomes a macrophage.