Significance of platelet and monocyte activation for therapeutic immunoglobulin-induced thromboembolism

Objectives

Thromboembolic events (TEE) in patients receiving infusions of intravenous immunoglobulin (IVIG) products have recently been associated with contaminating factor XIa. We studied whether platelet and monocyte activation could also be involved.

Methods

Twenty IVIG samples from five manufacturers were tested for the induction of visible whole blood clot formation. A selection of TEE-associated and not associated lots was further analyzed for effects on thromboelastometry, platelet activation and adhesion, as well as monocyte tissue factor surface expression. Pure factor XIa was included for comparison. Western blotting was applied to analyze anti-CD154-reactive proteins in IVIG.

Results

In whole blood, IVIG enhanced macroscopic clotting additively with factor XIa. In monocytes, all IVIG products induced the FcγRII-dependent tissue factor expression to a similar extent, which was not affected by addition of factor XIa. Testing platelet aggregation, IVIG strengthened the ADP and TRAP-6-elicited response. Furthermore, IVIG increased platelet-monocyte adhesion and annexin V binding to platelet microvesicles, and promoted platelet adhesion to IVIG-coated surfaces. The strongest effects were observed with TEE-associated lots. CD154-related proteins were detected in all IVIG products. CD154-related high molecular weight complexes were particularly found in the TEE-associated IVIG. In platelet aggregation, recombinant soluble CD154 enhanced aggregate formation and stability.

Conclusion

Our data demonstrate that IVIG modulate platelet and monocyte activation and can thereby affect the hemostatic balance. These effects are either additive to or independent from factor XIa. CD154-related proteins are assumed to be involved in these interactions, the mechanism of which needs to be elucidated in further studies.     

When Genetic Load Does Not Correlate with Phenotypic Spectrum: Lessons from the GnRH Receptor (GNRHR)

Context: A broad spectrum of GnRH-deficient phenotypes has been identified in individuals with both mono- and biallelic GNRHR mutations. Objective: The objective of the study was to determine the correlation between the severity of the reproductive phenotype(s) and the number and functional severity of rare sequence variants in GNRHR. Subjects: Eight hundred sixty-three probands with different forms of GnRH deficiency, 46 family members and 422 controls were screened for GNRHR mutations. The 70 subjects (32 patients and 38 family members) harboring mutations were divided into four groups (G1-G4) based on the functional severity of the mutations (complete or partial loss of function) and the number of affected alleles (monoallelic or biallelic) with mutations, and these classes were mapped on their clinical phenotypes. Results: The prevalence of heterozygous rare sequence variants in GNRHR was significantly higher in probands vs. controls (P < 0.01). Among the G1-G3 groups (homozygous subjects with successively decreasing severity and number of mutations), the hypogonadotropic phenotype related to their genetic load. In contrast, subjects in G4, with only monoallelic mutations, demonstrated a greater diversity of clinical phenotypes. Conclusions: In patients with GnRH deficiency and biallelic mutations in GNRHR, genetic burden defined by severity and dose is associated with clinical phenotype. In contrast, for patients with monoallelic GNRHR mutations this correlation does not hold. Taken together, these data indicate that as-yet-unidentified genetic and/or environmental factors may combine with singly mutated GNRHR alleles to produce reproductive phenotypes.