Determinants of persistence in canine distemper viruses

The history of immunohistochemistry started in 1941 when Coons identified pneumococci using a direct fluorescent method. Then followed the indirect method, the addition of horseradish peroxidase, the peroxidase anti-peroxidase technique of 1979 and the use of the Avidin and Biotin complex in the early 1980s. This sequence of events can help one appreciate the differences in these various techniques and their increased sophistication and sensitivity. The technique has been applied in the field of safety evaluation of new pharmaceutical products. Examples of current projects are used to illustrate the scope of the application. The use of an antibody to detect proliferating cell nuclear antigen has, in a pilot study with the popliteal lymph node assay, provided a method of differentiating an irritant response to acetone from an immune response to hydrazine. In hydrazine-treated rats the proliferation is mainly in the follicular region whilst it is mainly sinusoidal in animals treated with acetone. In the guinea-pig maximisation test, initial work with dinitrochlorobenzene suggests that detection of Langerhans cells may aid the differentiation of an irritant from an immune response. The preclinical assessment of antibodies intended for therapeutic use in man requires immunohistochemistry to be used to identify any human tissues which show a cross-reactivity. The major problems are not in the test itself but in obtaining suitable material. Identification of hormones is a useful tool for assessing the effects of releasing factors and has proved useful in aiding tumour identification in routine carcinogenicity studies. In a rare case, detection of prolactin in cell deposits in the lungs of a rat confirmed that this was a metastasis from a pituitary carcinoma. The application of immunohistochemical techniques to preclinical assessment of drugs should always be considered. In particular, it is recommended that appropriate samples should be conserved from routine studies in order to permit these techniques to be performed, if considered appropriate in the light of findings during routine histological examination.