Antiidiotype antibody against platelet anti-GPIIIa contributes to the regulation of thrombocytopenia in HIV-1-ITP patients.
Patients with human immunodeficiency virus 1-associated immunological thrombocytopenia (HIV-1-ITP) have markedly elevated platelet-bound immunoglobulin (Ig)G, IgM, and C3C4, as well as serum circulating immune complexes (CICs) composed of the same. Affinity purification of IgGs from their CICs with fixed platelets reveals high-affinity antibody (Ab) against platelet glycoprotein (GP)IIIa 49-66, which correlates inversely with their platelet count. However, sera from these patients have little to no anti-GPIIIa activity. To investigate this, we assayed serum, purified serum IgG, and CIC-Ig from these patients. This revealed approximately 150-fold greater Ab activity in purified serum IgG, and approximately 4,000-fold greater reactivity in CIC-IgG. This was shown to be associated with the presence of antiidiotype Ab2 (both IgG and IgM) sequestered in the CIC-IgG. The IgM antiidiotype was predominantly blocking Ab, as demonstrated by specificity for F(ab')(2) fragments of anti-GPIIIa 49-66 of HIV-1-ITP patients and inhibition of reactivity with peptide GPIIIa 49-66, not with a control peptide. The IgM antiidiotype was not polyreactive. Similar measurements were made in nonthrombocytopenic HIV-1-infected patients. Their serum reactivity was not measurable, but serum Ig and CIC-IgG against platelet GPIIIa 49-66 was present, although considerably lower than that found in HIV-1-ITP patients (26- and 35-fold lower, respectively). In addition, their IgM antiidiotype reactivity was 12-fold greater than that found in HIV-1-ITP patients. The IgM antiidiotype Ab titer of both cohorts correlated with in vivo platelet count (r = 0.7, P = 0. 0001, n = 32). To test the in vivo effectiveness of the IgM antiidiotype, thrombocytopenia was induced in mice with 25 microgram of affinity-purified anti-GPIIIa 49-66 (mouse GPIIIa has 83% homology with human GPIIIa and Fc receptors for human IgG1). Maximum effect was obtained at 4-6 h after intraperitoneal injection into Balb/c mice with a platelet count of approximately 30% baseline value. Preincubation of the anti-GPIIIa Ab with control IgM at molar ratios of IgM/IgG of 1:7 before intraperitoneal injection had no effect on the in vivo platelet count, whereas preincubation with patient IgM antiidiotype improved the platelet count to 50-80% of normal. Thrombocytopenia could be reversed after addition of IgM antiidiotype 4 h after induction of thrombocytopenia. Thus, CICs of HIV-1-infected patients contain IgM antiidiotype Ab against anti-GPIIIa, which appears to regulate their serum reactivity in vitro and their level of thrombocytopenia in vivo.
Nardi
M
M
Department of Medicine, New York University Medical Center, New York, New York 10016, USA.
Karpatkin
S
S
D000328:Adult; D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000032:analysis* / Q000627:therapeutic use; D000936:Antigen-Antibody Complex / Q000097:blood; D015551:Autoimmunity; D015658:HIV Infections / Q000150:complications / Q000276:immunology*; D015497:HIV-1; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D008297:Male; D051379:Mice; D010446:Peptide Fragments / Q000276:immunology*; D010976:Platelet Count; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins / Q000276:immunology*; D013921:Thrombocytopenia / Q000150:complications / Q000276:immunology* / Q000628:therapy
D000888:Antibodies, Anti-Idiotypic; D000936:Antigen-Antibody Complex; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; C106958:platelet glycoprotein (GP)IIIa 49-66