The development of inhibitory antibodies against factor VIII (FVIII) is the major complication in the treatment of hemophilia A patients with FVIII products. Immune Tolerance Induction (ITI) therapy using long-term application of high doses of FVIII has evolved as an effective therapy to eradicate the antibodies and induce long-lasting immune tolerance. It is a common observation that infections, particularly central venous catheter infections during ITI cause a rise in anti-FVIII antibody titers that can prolong the course of ITI or possibly even lead to failure of ITI. Based on this observation, we asked the question whether microbial components derived from viruses or bacteria modulate the re-stimulation of FVIII-specific immune memory and disturb the recently described inhibition of memory-B-cell-re-stimulation by high doses of FVIII (
Hausl et al.: Blood 2005; in press
). Microbial components are recognized by toll-like receptors (TLRs) that serve as an important link between innate and adaptive immunity. TLRs can discriminate various microbial components such as lipopeptides derived from bacteria or zymosan derived from yeast (recognized by TLR1/2 or TLR2/6), double-stranded RNA derived from viruses (recognized by TLR3), lipopolysaccharide (LPS) derived from gram-negative bacteria (recognized by TLR4), flagellin derived from bacterial flagella (recognized by TLR5), single-stranded RNA derived from viruses (recognized by TLR7/8) or bacterial DNA containing the unmethylated CpG motif (recognized by TLR9). We analyzed the re-stimulation of FVIII-specific memory-B cells using a murine model of hemophilia A as described previously (Hausl et al.: Blood 2004; 104:115–22
; Hausl et al.: Blood 2005, in press
). The following TLR ligands were tested: zymosan for TLR2 (0.1–10,000 ng/ml), poly I:C for TLR3 (1.0–50,000 ng/ml), LPS for TLR4 (0.1–10,000 ng/ml), Flagellin for TLR5 (0.01–1,000 ng/ml), Loxoribine for TLR7 (1.0–50,000 ng/ml) and CpG oligonucleotides for TLR9 (0.1–10,000 ng/ml). Our results indicate that none of the TLR ligands at the concentrations tested induced a significant re-stimulation of FVIII-specific memory B cells in the complete absence of either FVIII or T cells. However, ligands for TLR3, TLR4, TLR7 and TLR9 were able to disturb the inhibition of memory-B-cell-re-stimulation by high doses of FVIII and amplified the re-stimulation induced by low doses of FVIII substantially.We conclude that triggering of TLRs by microbial components that are present during infections amplify the re-stimulation of FVIII-specific memory B-cells induced by low doses of FVIII and disturb the inhibition induced by high doses of FVIII.
