Immunohistology of sarcoid CD3
T-cells and FOXP3 expression. A–C Sections of formalin fixed sarcoid tissue stained using anti-CD3 antibody and peroxidase anti-rabbit antibodies developed with DAB substrate. A A low power image (×100) Brown CD3+ T-cells are present throughout the tumour. B A higher power image (×200) showing the CD3+ positive brown staining of cell membranes surrounding a clear cytoplasm and nucleus typical of activated T-cell blasts. C An area of dense T-cell infiltration surrounding a blood vessel (×200). D Frozen section of sarcoid tissue showing texas-red CD3+ T-cells and separate green FITC stained BPV E2 superimposed on blue DAPI nuclear staining. E Formalin fixed section of normal equine skin stained with rabbit anti-FOXP3 peroxidase using DAB substrate. The nuclei of cells in the dermis do not express FOXP3, the epidermis shows a diffuse background staining of the keratin, the basal cells contain brown melanin granules but there nuclei are negative for FOXP3 and visible with blue counterstain some FOXP3 positive nuclei are present in the stratum spinosum (arrow). F Formalin fixed section of equine sarcoid stained with rabbit anti-FOXP3, the majority of nuclei in the tumour are dark brown indicating they express FOXP3. The FOXP3 staining extends into the nuclei of some basal cells within the epidermis and the stratum spinosum.