Purely visually, one cannot tell resting B- and T-lymphocytes apart. For diagnostic purposes, however, the two populations of lymphocytes can be distinguished based on their plasma membrane proteins . For this, an antibody against the thy-1-glycoprotein that is present on the T cells is used. With the same immunohistochemical technique the maturity of cells can also be assessed, because according to how mature the cell is, various surface proteins are produced (see: differentiation of the receptor on T-lymphocytes in the thymus ( interactive diagram, 40 kb ) and differentiation of the receptors on B-lymphocytes in bone marrow ( interactive diagram, 100 kb ). By stimulating B or T cells the difference is also visible. The B cell, which due to the stimulation has transformed into a plasma cell, is completely full of rER, and appears larger. The T cell remains the same size and possesses little rER; however, it has many free ribosomes.