Unique processing pathways within recipient antigen-presenting cells determine IgG immunity against donor platelet MHC antigens.
Recipient IgG immunity against leukoreduced donor platelets is dependent on indirect T-cell allorecognition and is suppressed in vivo by inhibitors (aminoguanidine, AMG) of inducible nitric oxide synthase (iNOS). To examine recipient processing pathways of donor platelet antigens, enriched macrophages (antigen-presenting cells [APC]) from BALB/c (H-2(d)) mice were pulsed with allogeneic C57BL/6 (H-2(b)) platelets and transfused weekly into naive BALB/c mice. Platelet-pulsed APC stimulated IgG antidonor antibody production in 45% of recipients by the second transfusion and in 100% by the sixth transfusion; this response was enhanced by pulsing in the presence of interferon-gamma. By the sixth transfusion, high-titer IgG1 (mean titer 4990) and IgG2a (1933) isotypes specific for donor major histocompatibility complex (MHC) class I antigens were detected. Platelet pulsing in the presence of AMG or colchicine significantly inhibited the ability of APC to stimulate IgG alloantibodies; only 50% (P <.005) and 20% (P <.0001) of recipients, respectively, produced antibodies by the sixth transfusion. AMG inhibition was reversed by the addition of L-arginine, the substrate for iNOS. In contrast, pulsing in the presence of chloroquine, the proteasome inhibitory peptide MG115, or Brefeldin A enhanced APC immunity (70-100% of recipients antibody positive by the second transfusion [P <.05]); these agents allowed the pulsed APC to stimulate IgG2a but inhibited IgG1 production and this correlated with a reduction in serum interleukin (IL)-4 levels. The results suggest that for donor platelet antigens to stimulate IgG alloantibodies, recipient APC use the essential generation of nitric oxide and a noncytosolic, pH-independent processing pathway, which can be exploited as an effective immunotherapy target to further inhibit alloimmunization against leukoreduced platelets. (Blood. 2000;95:1735-1742)
Bang
K W
KW
Department of Laboratory Medicine and Pathobiology, St. Michael's Hospital, Toronto, Ontario, Canada.
Speck
E R
ER
Blanchette
V S
VS
Freedman
J
J
Semple
J W
JW
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000918:Antibody Specificity; D017951:Antigen Presentation; D000938:Antigen-Presenting Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D001782:Blood Donors; D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology*; D020126:Brefeldin A / Q000494:pharmacology; D002738:Chloroquine / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D006183:H-2 Antigens / Q000276:immunology / Q000378:metabolism*; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000276:immunology*; D015847:Interleukin-4 / Q000097:blood; D007518:Isoantibodies / Q000096:biosynthesis* / Q000276:immunology; D007976:Leupeptins / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008870:Microtubules / Q000502:physiology; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D017713:Platelet Transfusion; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology; D014404:Tubulin / Q000502:physiology
D006183:H-2 Antigens; D007074:Immunoglobulin G; D007518:Isoantibodies; D007976:Leupeptins; D014404:Tubulin; C089486:carbobenzoxy-leucyl-leucyl-norvalinal; D000643:Ammonium Chloride; D020126:Brefeldin A; D015847:Interleukin-4; D009569:Nitric Oxide; D002738:Chloroquine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D003078:Colchicine