Use of antibodies against LH receptor, 3 beta-hydroxysteroid dehydrogenaseand vimentin to characterize different types of testicular tumour in dogs

Testicular tumours in dogs are of Sertoli cell, Leydig cell or germinal ori gin and mixed tumours are also frequently observed. The cellular components of mixed tumours are usually identified by histological examination but so metimes this is difficult. In this study, a panel of specific antibodies wa s used to identify the different cell types in testicular tumours by immuno histochemistry. Leydig cells were identified using an antibody against the LH receptor and an antibody against the steroidogenic enzyme 3 beta -hydrox ysteroid dehydrogenase (3 beta -HSD), both of which are characteristic of L eydig cells in testes. Sertoli cells were identified using an antibody agai nst the intermediate filament vimentin. Seminoma cells did not stain with a ny of these antibodies. Vimentin was used only in histologically complex ca ses. Eighty-six tumours, diagnosed histologically as 29 Sertoli cell tumour s, 25 Leydig cell tumours, 19 seminomas and 13 mixed tumours, were studied. Feminization was observed in 17 dogs. Leydig cell tumours stained positive ly with the antibodies against the LH receptor and 3 beta -HSD, whereas sem inomas and Sertoli cell tumours were negative (unstained). The antibody aga inst vimentin stained both Sertoli and Leydig cells, and tumours arising fr om these cells, but not seminomas. Immunohistochemistry revealed that three tumours identified histologically as Sertoli cell tumours were actually Le ydig cell tumours. In 14 dogs the histological diagnosis appeared to be inc omplete, as mixed tumours instead of pure types of tumours were identified in 11 dogs, and in three dogs mixed tumours appeared to be pure types. Henc e, the histological diagnosis was insufficient in approximately 20% of dogs . Furthermore, immunohistochemical analysis of testis tumours revealed that feminization occurred in dogs with Sertoli cell tumours or Leydig cell tum ours and their combinations, but not in dogs with a seminoma. In conclusion , incubation with antibodies against LH receptor and SP-HSD proved to be a consistently reliable method for identification of Leydig cell tumours in d ogs. Vimentin can be used to discriminate between Sertoli cell tumours and seminomas. Overall, this panel of antibodies can be very useful for determi nation of the identity of testicular tumours in which histological characte rization is complicated and the pathogenesis of feminization is not clear.