Comment on “Frequency of Epitope-Specific Naive CD4+ T Cells Correlates with Immunodominance in the Human Memory Repertoire”

Abstract

W e read the article by Szymczak-Workman et al. (1) with great interest. They have concluded that apoptosis of effector CD4 T cells is not involved in CD4 1 Foxp3 1 CD25 1 regulatory T cell (Treg)-mediated suppression, despite several studies showing the pivotal role of Treg-mediated apoptosis in immune suppression (2–6). Since the authors' experimental conditions differed from our work (4), we tested different T cell activation conditions for Treg sup-pression (7). We found proliferative suppression consistently associated with apoptosis of T responder (Tresp) cells as previously reported (Fig. 1A, 1B) (4). Using the CD4 Tresp cells from Bim knockout (BKO) mice obtained from The FIGURE 1. CD45.2 CD4 + CD25 2 (Tresp), control CD45.1 CD4 + CD25 2 (Tcon), and CD45.1 CD4 + CD25 + (Treg) cells were FACS sorted from spleen. Tresp cells were cultured alone or in cocultures with Tcons or Tregs at a 1:1 ratio. (A) The cells were stimulated using soluble anti-CD3 Ab (0.5 mg/ml) along with anti-CD28 Ab (2 mg/ml) (a), anti-CD3 Ab along with APC (b), or anti-CD3 Ab along with anti-CD28 Ab and APC (c). Live cell proliferation (left) and the percentage of Treg-induced apoptosis (right) of CFSE-labeled Tresp cells, as detected 4 d after culture. (B) The cells were stimulated using indicated concentrations of soluble anti-CD3 Ab and 2 mg/ml of anti-CD28. IL-2 was added where indicated. (C) The cells were stimulated using indicated concentrations (0.5 or 5 mg/ml) of soluble anti-CD3 Ab and 2 mg/ml of anti-CD28 and APC for 66 or 96 h. Percentage Tresp apoptosis (upper panel), CFSE 1 propidium iodide 2 Tresp live cell counts (lower panel) or proliferation (right) of CD45.2 Tresps, as measured by flow cytometry in equal volumes of cells