Uveitis caused by cytotoxic immune response to cutaneous malignant melanoma in swine: destruction of uveal melanocytes during tumor regression.

In a substrain of Sinclair miniature black swine, bred for increasing incidence of cutaneous malignant melanomas, tumor regression occurs spontaneously and is accompanied by depigmentation of the skin, hair, and eyes. We conducted a 12-month longitudinal study of the ocular phenomena in 30 swine beginning at 3 weeks of age. The clinically observed sequence of depigmentation of the fundus and iris was correlated with histopathologic changes in selected enucleated eyes. Normal melanocytes of the uveal tract are destroyed between the 4th and 16th week of life. Melanocyte destruction is preceded by an invasion of the uveal tract by mononuclear cells having the ultrastructural features of lymphocytes and monocytes. Melanin and other cellular debris of ruptured melanocytes are ingested by macrophages which then migrate to the walls of blood vessels. Cataracts and band keratopathy develop secondary to the uveitis in some animals. Pilot electroretinograms show diminished electrical activity in photoreceptors of totally depigmented eyes possibly indicating ischemic or toxic damage to the retina. The retinal pigment epithelium remains essentially normal during the acute stages of uveal inflammation; later some damage and reparative hyperplasia may occur. The death of normal uveal melanocytes that occurs during the systemic attack on the cutaneous malignant melanomas appears to be an "innocent bystander" error in the immune recognition mechanism. The antigenic basis of this immunologic cross reaction is under investigation.

Effect of neutral conditioning on racial attitudes of children.

The purpose of this experiment was to test the effectiveness of classical conditioning procedures in reducing negative evaluative responses, i.e., attitudes, toward pictures of Afro-American people. Ss were 73 Euro-American kindergarten children who received either 0, 1, 4, or 8 conditioning sessions of 36 pairings of the color black with neutral words. Two racial attitude scales were employed to measure amount of change in Ss' racial attitudes after exposure to the conditiong procedures. Parish's (1972) Revised PRAM II did not detect any change, but Williams' (1971) PRAM II demonstrated a significant reduction in anti-Afro-American attitudes for those Ss who received 8 conditioning sessions.