Noncytolytic human lymphocytes injure dermal microvessels in the huPBL-SCID skin graft model

Recent transplantation experiments using perforin-deficient mice as allogra ft recipients have challenged the concept that allograft rejection is media ted exclusively by CTL. We sought to determine if human noncytolytic lympho cytes could mediate rejection of allogeneic human skin grafts in the huPBL- SCID mouse model of rejection. We generated short term lines of human lymph ocytes from peripheral blood mononuclear cells using PHA as a mitogen. The first group was stimulated with PHA alone, the second with PHA plus IL-4 an d neutralizing antibody to IL-12, and in the third group PBL were depleted of B cells and monocytes before stimulation as in group 2. After two passag es, lines were tested for cytolytic ability and IFN-gamma production. Each line was injected i.p. to mice bearing allogeneic skin grafts. The grafts w ere harvested between day 16 and 21 after PBL injection, then the histology was scored by a blinded observer for degree of infiltration, microvessel i njury, induction of epidermal MHC class II, and perforin expression. In vit ro we found that PBL in groups 2 and 3 were unable to lyse cultured endothe lial cells in a lectin-directed In-111 release assay. In vivo 80% of the IL -4/anti-IL-12 groups maintained the IFN-gamma -low phenotype, and no perfor in was detected in these grafts. Nevertheless, human microvessel injury was similar between the two groups. This was not antibody-dependent since the B-cell-depleted group showed similar injury. Moreover adjacent murine vesse ls were intact. We interpret these observations to show (1) these human PBL lines maintained their phenotype following in vivo restimulation, and (2) noncytolytic graft-infiltrating lymphocytes specifically promote injury of allogeneic human microvessels. Human Immunology 62 598-606 (2001). (C) Amer ican Society for Histocompatibility and Immunogenetics, 2001. published by Elsevier Science Inc.