7 - LFA-1/ICAM-1 Adhesion Pathway is Involved in Both Apoptosis and Proliferation of Thymocytes Induced by Thymic Dendritic Cells

Abstract

This chapter presents a study to demonstrate that purified rat thymic dendritic cells (TDC) promote thymocyte apoptosis in vitro and also stimulate thymocyte proliferation. For this study, thymocyte suspension was obtained by teasing thymuses of adult of 8–10 weeks old Albino Oxford (AO) rats against a steel mesh using RPMI medium with 10% FCS. TDC were isolated from the obtained thymocyte suspension as low-density cells after centrifugation over a Nycodenz gradient. Suspensions of TDC and thymocytes (ratio 1:5) were cultivated for 24 hours at 37º C in quadruplicate in 96-well round plates. The study found that apoptosis is inhibited by mAbs to LFA-1 (CD11a and CD18) and ICAM-1, which might be a consequence of inhibition of thymocyte binding to TDC. The TDC also stimulate the proliferation of thymocytes without any additional stimuli, which was potentiated by using IL-2, anti-aβ TCR (R-73), phorbol myristate acetate (PMA), or a calcium ionophore. The TDC-induced proliferation was inhibited by anti-CD18 monoclonal antibody (mAb) and stimulated by anti-CD11a mAb. In contrast, anti-ICAM-1 mAb shows a differential effect on thymocyte proliferation, depending on applied stimuli.