title: Partial T-cell activation and anergy induction by polyclonal antithymocyte globulin.
abstract: BACKGROUND
  Polyclonal antithymocyte globulins have been assumed to deplete or sequester immunocompetent T cells. We investigated the hypothesis that anti-human thymocyte globulin (ATGAM)-mediated immunosuppression is delivered via nondepletive, immunologically specific actions as a consequence of simultaneous engagement of multiple T cell receptors.
  
  
  METHODS
  Purified T cells obtained from healthy volunteers or renal transplant recipients receiving their first dose of ATGAM were evaluated for proliferative responses and cell-mediated lympholysis. ATGAM binding and receptor expression were determined by flow cytometry. Cytokines and ATGAM levels were measured by enzyme-linked immunosorbent assay.
  
  
  RESULTS
  ATGAM-treated T cells showed significant dose-dependent inhibition of proliferation in vitro at concentrations comparable to those measured in patients. Effectors raised after ATGAM treatment failed to develop cytotoxicity. Supernatant interleukin (IL)-2 levels in ATGAM-treated cultures were significantly reduced (P<0.01 vs. control). IL-4 was not significantly altered. In vivo studies confirmed significant ATGAM-mediated inhibition of proliferative responses. Concanavalin A and OKT3-driven proliferation were reduced 30-60% by ATGAM. Flow cytometry showed that ATGAM recognized multiple cell surface receptors and resulted in markedly increased IL-2R and CD28 expression in the absence of proliferation, demonstrating partial T-cell activation. ATGAM synergized with phorbol myristate acetate to produce strong proliferation, which suggests that it provides a calcium-based signal resulting in anergy.
  
  
  CONCLUSIONS
  ATGAM recognizes and cross-links multiple cell surface receptors and costimulator molecules on human T cells. Simultaneous engagement by ATGAM in the context of allogeneic or mitogenic stimulation leads to partial T-cell activation and anergy.
authors.affiliation: Department of Surgery, University of Michigan Medical School, Ann Arbor 48109, USA. merionb@umich.edu
authors.forename: R M
authors.initials: RM
authors.lastname: Merion
authors.forename: T
authors.initials: T
authors.lastname: Howell
authors.forename: J S
authors.initials: JS
authors.lastname: Bromberg
mesh_terms: D000961:Antilymphocyte Serum / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D006801:Humans; D007107:Immune System / Q000187:drug effects*; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007376:Interleukin-2 / Q000037:antagonists & inhibitors; D015847:Interleukin-4 / Q000378:metabolism; D008213:Lymphocyte Activation / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology
chemical_list: D000961:Antilymphocyte Serum; D007166:Immunosuppressive Agents; D007376:Interleukin-2; D011956:Receptors, Cell Surface; D015847:Interleukin-4