EFFECTS OF THYMOSIN ALPHA-1 ON THE DEVELOPMENT OF AMEBOID MICROGLIAL CELLS IN THE CORPUS-CALLOSUM OF NEONATAL BALB C AND ATHYMIC MICE/

The present study investigated the effects of intraperitoneal injectio ns of thymosin alpha 1 on the supraventricular amoeboid microglial cel ls (SAMC) in the newborn athymic and normal BALB/c mice. The microglia l cells labelled by the lectin GSA I-B4 and the antibody Mac-1 showed a 27% reduction in number in the athymic mice receiving thymosin alpha 1 injections compared with those receiving vehicle injections, and a 37% reduction in BALB/c mice receiving thymosin alpha 1 injections com pared with those receiving vehicle injections. Some of the SAMC in bot h BALB/c and athymic mice receiving thymosin alpha 1 injections became ramified, while the remainder still exhibited their normal amoeboid a ppearance with few filopodial processes. Ultrastructurally, the lectin reaction product was confined to the plasma membrane and some cytopla smic vacuoles of labelled SAMC. In both BALB/c and athymic mice, some labelled microglial cells became slender or elongated after thymosin a lpha 1 injections. Also their cytoplasm was reduced and contained fewe r organelles. Radioimmunoassay of the plasma of thymosin alpha 1 and v ehicle-injected mice showed that there was a significant increase in t he cortisol level in BALB/c (P < 0.01) and athymic (P < 0.001) mice 5 days after thymosin alpha 1 injections, compared with that of the cont rol mice. The results point to a strong correlation between the reduct ion of SAMC and the increased level of plasma cortisol. Supporting thi s is the fact that cortisol is known to suppress the production of mon ocytes considered to be the precursors of amoeboid microglia.