An Electron-Microscope Study of the in vitro Transformation of Human Leucocytes

The effect of retinol (vitamin A) on human lymphocytes stimulated by phytohaemagglutinin. An ultrastructural study

Retinol (Vitamin A) has been found to inhibit the stimulation of lymphocytes by certain mitogens. The ultrastructural morphology of phytohaemagglutinin-stimulated lymphocytes exposed to retinol 10 microgram/ml and 20 microgram/ml show that disaggregation of polyribosomes and formation of autophagic vacuoles ensue in the majority of the cells. Some of the lymphocyte clumps are unaffected and continue to show normal mitosis. The changes in the affected cell are similar to those seen in a cell undergoing hormonal involution and it is postulated that the effects of the retinol may be mediated by a retinol binding protein in the susceptible cells.

Production of lymphoid tissue in the rat brain by implants containing phytohemagglutinin

Large numbers of plasmacytes and lymphocytic cells develop at the tip of miniature pipettes containing phytohemagglutinin (PHA) implanted into the brain of adult Lewis rats. The accumulation of lymphoid elements is present in tissue exposed to PHA for 1 week, and it persists in animals which were allowed to survive up to 10 weeks. It did not occur around control or non-active implants. Lymphoid cells usually serve as a morphologic index of immune mediated phenomena, but no evidence was seen in the present study to indicate that they produce damage to axons, dendrites or glial cells of the central nervous system despite direct contact with them. Plasma cells in the brain appear to develop from "dark" cells resembling lymphocytes that migrate into the central nervous system from reactive lymphoid tissue near the tip o.f the implant. Nerve, glial and subependymal cells do not respond with mitogenic activity to PHA.