Investigations of the immunoglobulin subtype transformation of anti-heparin-platelet factor 4 antibodies during treatment with a low-molecular-weight heparin (clivarin) in orthopedic patients.
BACKGROUND
It is now widely accepted that the pathophysiology of heparin-induced thrombocytopenia (HIT) syndrome is mediated by the generation of a wide array of functional and molecularly heterogeneous anti-heparin-platelet factor 4 (AHPF4) antibodies that may mediate platelet and/or endothelial cell activation/destruction.


OBJECTIVE
We investigated the differential prevalence and functionality of AHPF4 immunoglobulin subtypes (IgA, IgG, and IgM) in plasmas obtained from orthopedic patients immobilized with Plaster-Cast and treated with clivarin (a low-molecular-weight heparin) in comparison to a placebo for the prophylaxis of deep-vein thrombosis.


METHODS
Clivarin was administered subcutaneously at a fixed daily dosage of 1750 U without any adjustment or loading dosage. Citrated plasmas were obtained at baseline, at 10 to 14 days, and at postbrace procedure (5-12 weeks). An enzyme-linked immunosorbent assay (ELISA) was used to quantitate the AHPF4 antibody titers. The functionality of the ELISA-positive samples was determined by a 14C-serotonin release assay (SRA).


RESULTS
In the ELISA test, 16 of 1073 samples (1.5%; 6 in clivarin and 10 in placebo groups) were positive for AHPF4 antibodies (mean optical density [OD] = 0.46 +/- 0.02). None of the ELISA-positive samples for AHPF4 antibodies could mediate platelet activation responses as determined by the SRA (0%-3% serotonin release, P >.10, n = 16). Through differential immunoglobulin subtype analysis of the samples positive for (cumulative) AHPF4 antibodies, we determined that their relative prevalence in plasma were as follows: IgM (mean OD = 0.71 +/- 0.13) > IgG (0.31 +/- 0.08) > IgA (0.14 +/- 0.02). Although there was no significant difference in the total antibody titers between clivarin and placebo groups, the antibody subtyping data showed conversion trends (ie, IgA [clivarin to placebo], IgG [placebo to clivarin], and IgM [clivarin to placebo]).


CONCLUSIONS
These observations indicate that even at reduced dosages, clivarin can shift the immunogenic up-regulation toward the IgG subpopulation; however, the IgG subtype is of a nonfunctional type of AHPF4 antibody and thus may not cause any HIT-related pathogenic responses.
Ahmad
Sarfraz
S
Loyola University of Chicago, Stritch School of Medicine, Maywood, Ill, USA.
Bacher
H Peter
HP
Lassen
Michael R
MR
Hoppensteadt
Debra A
DA
Leitz
Helen
H
Misselwitz
Frank
F
Walenga
Jeanine M
JM
Fareed
Jawed
J
D000293:Adolescent; D000888:Antibodies, Anti-Idiotypic / Q000378:metabolism; D000918:Antibody Specificity / Q000235:genetics / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005343:Fibrinolytic Agents / Q000276:immunology / Q000627:therapeutic use; D006493:Heparin / Q000276:immunology*; D006495:Heparin, Low-Molecular-Weight / Q000276:immunology / Q000627:therapeutic use*; D006801:Humans; D007070:Immunoglobulin A / Q000032:analysis / Q000096:biosynthesis / Q000276:immunology; D017578:Immunoglobulin Class Switching / Q000276:immunology*; D007074:Immunoglobulin G / Q000032:analysis / Q000096:biosynthesis / Q000276:immunology; D007132:Immunoglobulin Isotypes / Q000032:analysis* / Q000096:biosynthesis*; D007075:Immunoglobulin M / Q000032:analysis / Q000096:biosynthesis / Q000276:immunology; D009985:Orthopedics / Q000379:methods; D010978:Platelet Factor 4 / Q000276:immunology*; D013921:Thrombocytopenia / Q000139:chemically induced* / Q000517:prevention & control*; D020246:Venous Thrombosis / Q000517:prevention & control
D000888:Antibodies, Anti-Idiotypic; D005343:Fibrinolytic Agents; D006495:Heparin, Low-Molecular-Weight; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D010978:Platelet Factor 4; C094240:reviparin; D006493:Heparin