Phenotype analysis of lymphoid cells in Marek's disease of CD4⁺or CD8⁺T‐cell‐deficient chickens: Occurrence of double negative T‐cell tumour

Chickens rendered either CD4(+) or CD8(+) T-cell-deficient by thymectomy and subsequent inoculation of anti-CD4 or anti-CD8 monoclonal antibody (mAb), were infected with Marek's disease herpesvirus (MDV). All the non-treated control (4/4) and CD8-deficient chickens (5/5) formed gross tumours. However, one of three CD4(+) T-cell-deficient chickens developed gross tumours. Histologically, all chickens had tumourous lesions in the liver and nerve fibres. In CD4(+) T-cell-deficient chickens, the phenotypes were CD3(+)CD4(-)CD8(-)Vss1-alphassTCR(+) T-cells and CD3(-)CD4(-)CD8(-) cells. These findings indicate that the double negative T-cells (CD3(+) CD4(-) CD8(-)) and CD3(-) CD4(-) CD8(-) cells are transformed morphologically in addition to CD3(+) CD4(+) CD8(-) T-cells by MDV infection.