Introduction. A broken arm or wrist is usually caused by a fall onto an outstretched arm. It typically takes about six to eight weeks to heal in adults, and less time in children. Doctors refer to all breaks or cracks in bones as fractures.Go to your nearest accident and emergency (A&E) department if you think you or your child has broken a bone.t typically takes about six to eight weeks to heal in adults, and less time in children. Doctors refer to all breaks or cracks in bones as fractures. Go to your nearest accident and emergency (A&E) department if you think you or your child has broken a bone.
In contrast, the overwhelming majority of antigens for T cells are proteins, and these must be fragmented and recognized in association with MHC products expressed on the surface of nucleated cells, not in soluble form.
Each B cell and T cell is specific for a particular antigen. What this means is that each is able to bind to a particular molecular structure. The specificity of binding resides in a receptor for antigen: 1  the B cell receptor (BCR) for antigen and.2  the T cell receptor (TCR) respectively.3  They are integral membrane proteins. 4  They are present in thousands of identical copies exposed at the cell surface.5  They are made before the cell ever encounters an antigen.he process works like this: 1  The precursors of T cells â like all blood cells â are formed in the bone marrow. 2  These cells then migrate to the cortex of the thymus. 3  At this time they have neither a complete TCR nor either CD4 or CD8 (thus are called double-negative or DN cells).