Basic components of the immune system part 111

When these cells are stimulated by a specific antigen, a few of these resting cells undergo proliferation (activated cells) and the transformation of activated cells can be measured  by incorporation of radiolabeled thymidine into the DNA of the cells and the number of counts per minute measured in β-counter. More recently, these same activated cells can be measured by the number of cells expressing cell surface antigens using markers such as CD69.