Modulatory effects of octreotide on anti-CD3 and dexamethasone-induced apoptosis of murine thymocytes

In an attempt to elucidate the effects of somatostatin on two crucial proce sses that regulated T-cell differentiation and selection in thymus in this study, we investigated in vivo and in vitro the effects of octreotide (SMS 201-995) on dynamics of apoptosis, induced by dexamethasone (DEX) or by ant i-CD3 monoclonal antibodies (mAb). The data were estimated by analysis of a bsolute cellularity, DNA fragmentation and maturational stage of thymocytes , detecting the CD4 and/or CD8 and T cell receptor MR) expression on thymoc ytes. The results, obtained by estimation of subdiploid peak of DNA and lad der DNA formation, have shown that SMS given in vivo, may potentiate the ea rly phase of DEX-induced nuclear fragmentation (at 24 h), accelerating simu ltaneously the elimination of thymic cells with double positive (DP) CD4(hi gh) CD8(high) phenotype (expressed both as percentage and absolute number). On the contrary, SMS, given both in vivo and in vitro, down-regulated the late process (at 72 h) of nuclear fragmentation, induced by anti-CD3 mAb, m inimizing simultaneously the elimination of DP cells (expressed both as per centage and absolute number). In anti-CD3-treated cultures of thymocytes, S MS retarded also the elimination of immature thymocytes, expressing the TRC alpha/beta (low or intermediate) phenotype. The data emphasize that octreo tide might have important regulatory effect on processes of thymic differen tiation and maturation. which are crucial for T cell selection, induction o f tolerance and prevention of autoimmune diseases. (C) 2001 Elsevier Scienc e B.V. All rights reserved.