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-cells, like other white blood cells, are created in the bone marrow from stem cells. After maturation, B-cells are present in your blood and in your lymph nodes. Thre are two main types of lymphocytes, T-cells, and B-cells. When you have a CBC blood test done, the number and percentage of lymphocytes are reported, but there is no differentiation as to which are T-cells and which are B-cells.