The binding of autoantibodies (autoAbs) to interferon (IFN)-γ in people with mycobacterial diseases has become an emerging medical concern. Many patients display specific human leukocyte antigen (HLA) class II haplotypes, which suggests that a common T cell-dependent and B cell-dependent mechanism might underlie the production of specific anti-IFN-γ autoAbs. We show here that these autoAbs target a major epitope (amino acids 121-131, designated position (P)121-131) in a region crucial for IFN-γ receptor (IFN-γR) activation to impair IFN-γ-mediated activities. The amino acid sequence of this epitope is highly homologous to a stretch in the Noc2 protein of Aspergillus spp., which was cross-reactive with autoAbs from patients. Rats immunized with Aspergillus Noc2 developed antibodies that reacted with human IFN-γ. We generated an epitope-erased variant of IFN-γ (EE-IFN-γ), in which the major neutralizing epitope region was altered. The binding affinity of anti-IFN-γ autoAbs for EE-IFN-γ was reduced by about 40%, as compared to that for IFN-γ1-131. Moreover, EE-IFN-γ activated the IFN-γR downstream signaling pathway ex vivo, irrespectively of anti-IFN-γ autoAbs. In conclusion, we identified a common, crucial B cell epitope that bound to anti-IFN-γ autoAbs in patients, and we propose a molecular-mimicry model for autoAb development. In addition, treatment with EE-IFN-γ might be worth investigating in patients producing anti-IFN-γ autoAbs.

examined, suggesting that the absence of functional T cells, rather than specifically CD247, affects NK differentiation. This observation is consistent with data from patients undergoing stem cell transplantation (SCT) in whom the first NK cells to repopulate the periphery have an immature phenotype and are less able to mediate cytotoxicity before T-cell recovery. 8 Interestingly, the ability of peripheral blood NK cells from the CD247-deficient patient to proliferate in mixed lymphocyte cultures in vitro was severely limited (see Fig E3 in this article's Online Repository at www.jacionline.org), but this phenotype could be reversed by IL-2 addition.During differentiation, the ability of NK cells to respond to stimulation is finely tuned in function of the repertoire of inhibitory and activating receptors expressed by each NK cell. 9 Because CD247 deficiency causes decreased expression and function of a range of activating NK receptors, impaired signaling might underlie the partial block of NK cell differentiation and NK cell hyporesponsiveness, which were observed in the CD247deficient patient. Importantly, similar changes in NK cell phenotype and function have not been seen in children with symptomatic congenital human cytomegalovirus (CMV) infection, 10 arguing against the hypothesis that the changes observed in the CD247-deficient patient are a consequence of CMV infection.Our observations have direct implications for the clinical management of immunodeficient patients. Even when not directly fatal, episodes of infectious disease delay transplantation and negatively affect the outcome. Thus, because NK cells play a critical role in antiviral immunity, the potentiation of NK cell function, for example by means of low-dose therapy with IL-2, could be a useful strategy to minimize infections and aid in the management of these patients until SCT.We thank all of the subjects who have contributed blood samples for these studies and Drs M. Lopez-Botet, J. Gil-Herrera, and M. L. Toribio for helpful discussion and advice.

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Formation of retinoblastoma, a cancer arising in the retinas of young children, is determined by mutational inactivation of an autosomal gene (RB), which has been molecularly cloned. Whereas all normal tissues and many tumor cells express an RB mRNA of 4.7 kilobases, six of six retinoblastomas were previously found either to lack RB gene expression or to have RB transcripts of abnormal (reduced) length. To further characterize the latter type of mutation, we chose to examine retinoblastoma cell line Y79, which expressed a shortened RB mRNA of about 4.0 kilobases. RB cDNA clones isolated from a library constructed with Y79 mRNA demonstrated an internal loss of470 nucleotides near the 5' end, which corresponded to a deletion of exons 2-6. Genomic clones containing the deletion junction were isolated from a library made with Y79 DNA, which allowed precise localization and sequencing of deletion endpoints in introns 1 and 6. These regions had no apparent homology to each other or to the Alu family of repetitive sequences, implying that the deletion must have occurred by a mechanism other than recombination of homologous sequences. Deletion of exons 2-6 would interrupt the open reading frame in RB mRNA and would result in premature termination of translation. Since no normal RB protein was detected by immunoprecipitation with specific antibody, the other, apparently normal RB allele in Y79 cells was necessarily inactivated by a different mutation.

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