IDENTIFICATION OF CELLS SECRETING A THYMOSTIMULIN-LIKE SUBSTANCE AND EXAMINATION OF SOME HISTOENZYMATIC PATHWAYS IN AGING AVIAN PRIMARY LYMPHATIC ORGANS .1. THYMUS

Thymi of adult chickens (White Leghorn strain), ages of 6, 18, 45, day s and 1, 3, 6, months, were studied by histological and histochemical stainings, histoenzymatic reactions (LDH, SDH, alpha-GPDH, NADH, NADPH , Ca++ dependent ATPase, pH 8.5) and by anti-thymostimulin immunoreact ion. Positive reactions for thymostimulin-like substance, mucopolysacc harides and enzymatic activities were located in different epithelial compartments of the cortical and medullary zones. In 3 and 6 month-old chickens, there was a progressive reduction of the cortical area and of the number of cortical and medullary epithelial cells, and, in the thymi of the 6 month-old chickens, a partial decline in the immunologi cal reactivity to anti-TS, but the intensity of the histochemical and enzymatic reactivities, in comparison with the thymi of the youngest c hickens, was not decreased. This may suggest that the cortical and med ullary epithelial cells still present in these thymi are capable of se creting and expressing activities and, thus, may maintain their functi ons.