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.
They are B lymphocytes (B cells) and T lymphocytes (T cells). B cells. B cells develop from bone marrow stem cells in adults. When B cells become activated due to the presence of a particular antigen, they create antibodies that are specific to that specific antigen.Antibodies are specialized proteins that travel thorough the bloodstream and are found in bodily fluids. cells develop from liver or bone marrow stem cells that mature in the thymus. These cells play a major role in cell mediated immunity. T cells contain proteins called T-cell receptors that populate the cell membrane. These receptors are capable of recognizing various types of antigens.