title: Extreme leukoreduction of major histocompatibility complex class II positive B cells enhances allogeneic platelet immunity.
abstract: In a murine model of platelet alloimmunization, we examined the definitive role that mononuclear cells (MC) have in modulating platelet immunity by using platelets from severe combined immunodeficient (SCID) mice. CB.17 (H-2(d)) SCID or BALB/c (H-2(d)) mouse platelets were transfused weekly into fully allogeneic CBA (H-2(k)) mice and antidonor antibodies measured by flow cytometry. MC levels in BALB/c platelets were 1.1 +/- 0.6/microL and SCID mouse platelets could be prepared to have significantly lower (<0. 05/microL) MC numbers. Transfusions with 10(8) BALB/c platelets (containing approximately 100 MC/transfusion) stimulated IgG antidonor antibodies in 100% of the recipients by the fifth transfusion, whereas 10(8) SCID mouse platelets (containing approximately 5 MC/transfusion) stimulated higher-titered IgG alloantibodies by the second transfusion. When titrations of BALB/c peripheral blood MC were added to the SCID mouse platelets, levels approaching 1 MC/microL reduced SCID platelet immunity to levels similar to BALB/c platelets. Characterization of the alloantibodies showed that the low levels of MC significantly influenced the isotype of the antidonor IgG; the presence of 1 MC/microL was associated with induction of noncomplement fixing IgG1 antidonor antibodies, whereas platelet transfusions, devoid of MC (<0. 05/microL), were responsible for complement-fixing IgG2a production. When magnetically sorted defined subpopulations of MC were added to the SCID platelets, major histocompatability complex (MHC) class II positive populations, particularly B cells, were found to be primarily responsible for the reduced SCID mouse platelet immunity. The presence of low numbers of MC within the platelets was also associated with an age-dependent reduction in platelet immunogenicity; this relationship however, was not observed with SCID mouse platelets devoid of MC. The results suggest that a residual number of MHC class II positive B cells within allogeneic platelets are required for maximally reducing alloimmunization.
authors.affiliation: Division of Hematology, St. Michael's Hospital and The Hospital for Sick Children, The University of Toronto and The Toronto Platelet Immunobiology Group, 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: D
authors.initials: D
authors.lastname: Cosgrave
authors.forename: A H
authors.initials: AH
authors.lastname: Lazarus
authors.forename: V S
authors.initials: VS
authors.lastname: Blanchette
authors.forename: J
authors.initials: J
authors.lastname: Freedman
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000032:analysis*; D007074:Immunoglobulin G / Q000097:blood; D007518:Isoantibodies / Q000097:blood; D007958:Leukocyte Count; D007963:Leukocytes, Mononuclear / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D016513:Mice, SCID; D017713:Platelet Transfusion
chemical_list: D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G; D007518:Isoantibodies