Question.

What is the significance of immunostaining with antibody to p53?

Answer.

First of all, p53 is the antigen in the tissue, with which the antibody combines (The p is for "protein"). p53 is also sometimes referred to as a TSG - Tumour Suppressor Gene). p53 was labelled "Molecule of the Year" by either Science or Nature about three years ago.

The "wild" type p53 is the normal. It suppresses cell transformation and/or mutations. It was traditionally considered to have a very short life and was therefore never present in concentrations large enough to demonstrate immunocytochemically. "Mutant" type p53 has a longer "half-life" and is therefore more easily demonstrated. It used to be that mutant type p53 was the antigen of interest. Then of course, things got more complicated.

There are, of course, antibodies to each type of p53 now. One thing is for sure - p53 is of fundamental importance in cell transformation. The biggest problem is that many consider that the expression of p53 is quantitatively related to prognosis and can therefore, be used to assess treatment outcomes. Whether quantitation should be by percentage of positive (?tumour) cells or by intensity of staining in the positive (?tumour) cells is still open to debate. Whichever it is, it is obviously important that your results of today can stand statistical comparison with your results of yesterday or tomorrow. Even more importantly, can they be used for comparisons with other labs? The patient may move elswhere for treatment, for example.

One thing I know for certain: it is very easy to make virtually all cells p53-positive - not just tumour cells - if you tweak your immunocytochemical method and any heat induced antigen retrieval you use. A real minefield!

Russ Allison, Wales
(Allison[AT]cardiff.ac.uk)