SUMMARY The monoclonal antibody NK1 C3, synthesised by the Netherlands Cancer Institute, has been used to assess its value in the diagnosis of melanocytic lesions. The antigen recognised by this antibody is not denatured by formalin fixation, with the result that the antibody can be used for retrospective studies on conventionally processed material.Positive results were obtained in primary melanoma (18/18), secondary melanoma (21/21), junctional and compound naevi (32/32), intradermal naevi (9/12), congenital naevi (3/3), so called dysplastic naevi (13/13), blue naevi (5/5), and Spitz tumours (3/14). Non-melanocytic tumours were tested for comparison. The results showed relative but not complete specificity of the antibody for melanocytic tumours, with positive results only in breast and prostate tumours (2/6 and 2/5 respectively). Negative results were obtained with basal and squamous cell carcinoma, appendage tumours, neural tumours, and apudomas.The staining pattern of NK1 C3 was compared with that of antibodies to S100 protein and to neurone specific enolase. Compared with S100 protein NK1 C3 gave stronger staining of a higher percentage of cells in the 12 specimens in which a direct comparison was made. Antibody raised against neurone specific enolase in sheep gave very poor results with heavy background staining. We suggest that NK1 C3 is a useful addition to the battery of monoclonal antibodies of value to the diagnostic histopathologist.In the past three years a large number of monoclonal antibodies have been raised against melanoma cells. Most have been raised against short term cell lines, or membrane fractions, and as a result tend to react with surface membrane antigens. These are often disrupted or destroyed by conventional histological fixation and preparation techniques, and as a result the antibodies react only with fresh frozen tissue. This is obviously a major disadvantage as far as routine surgical pathology is concerned, in that no retrospective studies on an unexpectedly pleomorphic tissue can be performed. Although the practice of surgeons and pathologists is evolving to utilise the "new morphology," with reservation of a small portion of frozen tissue for such work, those who work with primary malignant melanoma are understandably reluctant to divide up a specimen in such a way that the Breslow thickness measurement may be inaccurate. This problem does Accepted for publication 15 December 1983 not arise when one is dealing with a large tumour sample, but it does arise with small primary lesions in which the diagnosis is not clinically apparent.In this paper we report our experience with the use of the NK1 C3 monoclonal antibody as an aid to the diagnosis of melanocytic lesions. It does not discriminate between benign and malignant melanocytic lesions, but it does show a useful level of specificity for melanocytic versus non-melanocytic lesions. Material and methodsThe monoclonal antibody NK1 C3 was made available to us by Dr C Vennegoor and Dr P Rumke, to whom we express our gratitude....

Two monoclonal antibodies, NAI 34 and DA6 231, have been used as surface markers to count epidermal Langerhans cells in normal skin, allergic contact dermatitis, and mycosis fungoides of the plaque and poikilodermatous varieties. The antibodies recognized the HTA (human thymocyte antigen) and Ia antigens, respectively. In all situations the numbers of cells labeled by the two antibodies differed. In normal skin 75% of dendritic cells were labeled by both antibodies and 25% were labeled by NAI 34 alone. In contact dermatitis there is an increase in dendritic cells labeled by both antibodies and this pattern is also seen in untreated plaque stage mycosis fungoides. In poikilodermatous mycosis fungoides, striking staining of the epidermal keratinocytes with DA6 231 is seen with no dendritic cells labeled. Dendritic cells are, however, clearly seen with NAI 34 staining. Numbers of dendritic cells labeled by both antibodies fall during PUVA therapy.

Biopsies from twenty-three patients with malignant skin lesions and from twenty-two patients with premalignant or benign skin lesions were stained for beta2 microglobulin by use of the immunoperoxidase technique. The results showed a significant loss of demonstrable surface beta2 microglobulin from the surface of malignant cells compared to benign, and a partial loss in the premalignant cases. This difference could prove to be a useful tool in the histological diagnosis of malignant skin lesions, and in assessing whether or not the lesion has been completely excised.

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