Essential Requirements for the Validity of Immunocytochemical Staining Procedures

Although immunocytochemical results are rarely quantifiable today, it is well-recognized that the ultimate goal in many routine and research applications is quantitative measurement of tissue antigens. This trend is evident in several recent publications, even in the program of the present meeting. If immunocytochemistry is to be developed into a reliable quantitative method, it will be necessary to define and agree on criteria of reliability that could aid in both designing immunocytochemical experiments and interpreting the results. Criteria of reliability, based on long-established principles of quantitative biological assays, have been suggested a few years ago (Petrusz et al., 1980) and will be briefly summarized here. At the outset, it is important to realize (and accept the practical consequences of) the fact that there are definite limits to the exactness with which any observation can be made, whether quantitative or qualitative. In other words, all observations contain a certain component of error, and the magnitude and nature of this error is not always obvious from a single observation or even from repeated observations. Immunocytochemical staining in any form is a complex procedure, subject to many possible errors, and it is not always easy to obtain satisfactory results. Our goal must be to develop methods by which the errors can be evaluated and their influence on the final results can be determined. The criteria of reliability to be considered below (efficiency, accuracy, precision, sensitivity, and specificity) represent the first steps toward achieving this ultimate goal.