title: Indirect allorecognition of platelets by T helper cells during platelet transfusions correlates with anti-major histocompatibility complex antibody and cytotoxic T lymphocyte formation.
abstract: To study the cellular immunology of platelet-induced alloimmunization, a murine transfusion model was developed. BALB/c (H-2d) recipient mice were transfused weekly with 2 x 10(8) platelets or 10(3) leukocytes from C57BL/6 (H-2b) donor mice. Recipient antidonor major histocompatibility complex (MHC) class I alloantibodies could be detected in flow cytometric assays by the fifth platelet transfusion. In contrast, when leukocytes only were transfused, alloantibodies were not detected. In vitro assays demonstrated that murine H-2b platelets were positive for MHC class I expression but lacked MHC class II molecules on their membranes and were unable to stimulate proliferation or cytokine production when incubated with naive H-2d spleen cells. In vivo, however, platelet transfusions induced two distinct patterns of cell-mediated reactivity. First, during the initial transfusions and before alloantibody formation, there was induction of T-cell anergy, characterized by the inability of recipient T cells to respond to Concanavalin A (ConA) or to proliferate in an antidonor mixed lymphocyte reaction (MLR), together with suppressed natural killer (NK) cell activity. This unresponsiveness was associated with a transient increase in nitric oxide (NO)-dependent cytotoxicity and interleukin-1 (IL-1) production. Second, once alloantibodies developed, significantly increased antidonor CD8+ cytotoxic T lymphocyte (CTL) and NK cell responses were observed. At this time, when recipient spleen cells were depleted of CD8+ T cells and incubated with only donor platelets in 7-day antigen-presenting cell (APC) assays, enhanced proliferation and IL-2 production occurred. These cellular responses were not seen when 10(3) allogeneic leukocytes were transfused. Thus, the results suggest that leukoreduced platelet transfusions induce antidonor MHC antibodies and CD8+ CTL responses in recipient mice. At the same time, the transfusions induced recipient CD4+ T-cell activation when incubated with donor platelets in the presence of syngeneic APCs, an indirect recognition pathway that correlates with the time of alloantibody production.
authors.affiliation: Division of Hematology, St Michael's Hospital, Toronto, Ontario, Canada.
authors.forename: J W
authors.initials: JW
authors.lastname: Semple
authors.forename: E R
authors.initials: ER
authors.lastname: Speck
authors.forename: Y P
authors.initials: YP
authors.lastname: Milev
authors.forename: V
authors.initials: V
authors.lastname: Blanchette
authors.forename: J
authors.initials: J
authors.lastname: Freedman
mesh_terms: D000818:Animals; D016824:Antigens, Human Platelet / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D003208:Concanavalin A / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D006183:H-2 Antigens / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D007114:Immunization; D007375:Interleukin-1 / Q000097:blood; D007518:Isoantibodies / Q000096:biosynthesis / Q000276:immunology*; D008213:Lymphocyte Activation; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D017713:Platelet Transfusion; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D016824:Antigens, Human Platelet; D006183:H-2 Antigens; D000949:Histocompatibility Antigens Class II; C024138:I-E-antigen; D007375:Interleukin-1; D007518:Isoantibodies; D003208:Concanavalin A