The Use of Ferritin-Conjugated Antibodies in Electron Microscopy

Publisher Summary This chapter discusses the blocking technique as a control for the specificity of antigen–antibody reactions in tissue. If unconjugated antibody is applied, followed by the conjugate, there are very few free antigenic sites where tagging could occur. In actual practice, however, a relatively complete block is rarely seen. There is usually a reduction in the amount of tagging, but preparations are seldom devoid of ferritin. One of the major drawbacks associated with the use of ferritin-conjugated antibodies is their large size. Ferritin is approximately 100 A in diameter, whereas the antibody is about 250 A long and 35 A wide. To reduce the dimensions of the conjugate, ferritin is coupled with an active fragment of the antibody obtained by papain digestion. The challenge that remains is to develop techniques for labeling thin sections themselves. With this accomplishment, ease, consistency, and a high degree of specificity can be reached in the study of fine structure.