Uveitis in melanomatous swine: lack of evidence for humoral immune melanocyte destruction.

A strain of miniature Sinclair swine that have cutaneous malignant melanomas destroy their tumors via an immunologic process. Destruction of apparently normal melanocytes of the uveal tract occurs concurrently with tumor cell lysis. The authors investigated possible involvement of humoral antibodies in uveal melanocyte lysis. Uveal antigens solubilized by a variety of reagents were tested by immunodiffusion against autologous and homologous sera; no precipitation lines were found. Western blots of electrophoresed uveal proteins when tested against serum from an animal with a great tumor load showed no antigen-antibody reactions. No specific humoral antibodies were detected. Sera tested for immune complexes also were negative. Invasion of the uveal tract by mononuclear cells was quantified in 1-micron-thick sections of tissue taken at various stages of ocular depigmentation. Disappearance of melanocytes was preceded by an increase in mononuclear cells and followed by an increase in melanin-containing macrophages. The ultrastructural features of the invading cells are presented. The authors conclude that cell-mediated uveal melanocyte destruction is the most likely basis for the uveitis and other damaging sequelae.