Epitopes recognized by neutralizing therapy-induced human anti-interferon-alpha antibodies are localized within the N-terminal functional domain of recombinant interferon-alpha 2.

During prolonged recombinant interferon (rIFN)-alpha 2 therapy, a minority of patients develop high-titer neutralizing IFN-alpha antibodies. Sera from nine IFN-alpha antibody-positive patients were studied to characterize the specificity of anti-IFN-alpha neutralizing antibodies by their ability to inhibit the antiviral and antiproliferative activity of different rIFN-alpha subtypes and rIFN-alpha 1/alpha 2 hybrids. These therapy-induced antibodies (Tab) were compared with IFN-alpha-specific autoantibodies (Aab) from two patients with systemic lupus erythematosus who had never received any exogenous IFN-alpha. Although IFN-alpha subtypes are closely related in structure, Tab inhibited the antiviral activity of only recombinant (r)IFN-alpha 2 and rIFN-alpha 6, but not or slightly that of rIFN-alpha 1, -alpha 7, -alpha 8 and -alpha 14. Furthermore, of four different rIFN-alpha 1/alpha 2 hybrids tested, Tab inhibited only those which contained the N-terminal residues 17-64 of rIFN-alpha 2. Comparison of the primary sequences of neutralized and not neutralized subtypes suggests an epitope involving the residues 22-31 of IFN-alpha 2 is recognized. Thus, Tab block rIFN-alpha 2 by reacting with only one of two functional domains. In contrast, Aab possessed a broad specificity and neutralized both the antiviral and antiproliferative activity of rIFN-alpha 2, -alpha 6, -alpha 7, -alpha 8, and -alpha 14. They also neutralized all four rIFN-alpha 1/alpha 2 hybrids tested. These data demonstrate that Tab are highly specific for the therapeutic IFN-alpha subtype and specifically neutralize rIFN-alpha 2 by binding to its N-terminal functional domain.

The IgG binding site of human FcgammaRIIIB receptor involves CC' and FG loops of the membrane-proximal domain.

Fc gamma receptors for the Fc part of IgG are the mediators for antibody effector functions. FcgammaRIII and FcgammaRII are low affinity receptors that, through the interaction with immune complexes, initiate a variety of immunological responses, such as phagocytosis, antibody-dependent cellular cytotoxicity, and release of inflammatory mediators. We set out to define the IgG binding site on human FcgammaRIII. We assumed that potential beta-turns in Ig-like domains are the most probable determinants for ligand binding, and chimeric FcgammaRIIIB/FcepsilonRI receptors as well as single residue mutants were constructed in these regions of FcgammaRIIIB. Substitution of four amino acids in the membrane-proximal domain (Gln126, Arg156, Lys162, Val164) resulted in decreased binding of human IgG1. Lys162 and Val164 were found also to be crucial for the interaction with the IgG-binding inhibitory monoclonal antibody 3G8. In a putative three-dimensional model constructed in this study, these residues map on the CC loop (Gln126), on F beta-sheet (Arg156), and on the FG loop (Lys162, Val164). Our data are consistent with the study about human FcgammaRII (Hulett, M. D., Witort, E., Brinkworth, R. I., McKenzie, I. F. C., and Hogarth, P. M. (1994) J. Biol. Chem. 269, 15287-15293), suggesting that common structural determinants, i.e. FG loop or the GFC surface of the membrane-proximal domain, can be involved in interactions with IgG by both low affinity receptor classes FcgammaRII and FcgammaRIII.

Strong transient expression of the type I interferon-induced MxA protein in hepatitis A but not in acute hepatitis B and C.

The human MxA protein is a new specific marker for type I interferon activity both in vitro and in vivo. In the study presented here, this interferon-induced marker, as well as the 2',5'-oligoadenylate synthetases, was measured in circulating mononuclear cells from 21 patients with acute hepatitis A, 20 patients with acute hepatitis B and 14 patients with acute hepatitis C for determination of the activation of the interferon system in these viral diseases. In acute hepatitis A a strong expression (10 of 10 patients) of the MxA protein and the 2',5'-oligoadenylate synthetase activity in peripheral-blood mononuclear cells was observed during the first 2 wk after onset of clinical symptoms. In this period the MxA protein concentrations reached levels similar to those measured in patients treated with up to 5 x 10(6) IU interferon-alpha three times a week. Beyond wk 3, in eight of eight patients with hepatitis A no increased MxA protein levels were found. In contrast, peripheral-blood mononuclear cells from patients with acute hepatitis B contained either no measurable MxA protein or only slightly higher levels of the MxA protein, as did those of most patients (12 of 14) with acute hepatitis C. The MxA protein levels of both hepatitis B and C patients were significantly lower (p < 0.05) than those found in hepatitis A patients. Furthermore, sera from 6 of 10 patients with hepatitis A, but none of 10 patients with acute hepatitis B and C, contained measurable MxA protein. This serum MxA protein may originate from interferon-exposed and subsequently damaged liver cells.(ABSTRACT TRUNCATED AT 250 WORDS)