In a novel form of IFN-gamma receptor 1 deficiency, cell surface receptors fail to bind IFN-gamma

Complete IFN-gamma receptor ligand-binding chain (IFNgammaR1) deficiency is a life-threatening autosomal recessive immune disorder. Affected children invariably die of mycobacterial infection, unless bone marrow transplantation is undertaken. Pathogenic IFNGR1 mutations identified to date include nonsense and splice mutations and frameshift deletions and insertions. All result in a premature stop codon upstream from the segment encoding the transmembrane domain, precluding cell surface expression of the receptors. We report herein two sporadic and two familial cases of a novel form of complete IFNgammaR1 deficiency in which normal numbers of receptors are detected at the cell surface. Two in-frame deletions and two missense IFNGR1 mutations were identified in the segment encoding the extracellular ligand-binding domain of the receptor. Eight independent IFNgammaR1-specific mAb's, including seven blocking antibodies, gave recognition patterns that differed between patients, suggesting that different epitopes were altered by the mutations. No specific binding of (125)I-IFN-gamma to cells was observed in any patient, however, and the cells failed to respond to IFN-gamma. The mutations therefore cause complete IFNgammaR1 deficiency by disrupting the IFN-gamma-binding site without affecting surface expression. The detection of surface IFNgammaR1 molecules by specific antibodies, including blocking antibodies, does not exclude a diagnosis of complete IFNgammaR1 deficiency.

Partial interferon-gamma receptor signaling chain deficiency in a patient with bacille Calmette-Guérin and Mycobacterium abscessus infection

Complete deficiency of either of the two human interferon (IFN)-gamma receptor components, the ligand-binding IFN-gammaR1 chain and the signaling IFN-gammaR2 chain, is invariably associated with early-onset infection caused by bacille Calmette-Guérin vaccines and/or environmental nontuberculous mycobacteria, poor granuloma formation, and a fatal outcome in childhood. Partial IFN-gammaR1 deficiency is associated with a milder histopathologic and clinical phenotype. Cells from a 20-year-old healthy person with a history of curable infections due to bacille Calmette-Guérin and Mycobacterium abscessus and mature granulomas in childhood were investigated. There was a homozygous nucleotide substitution in IFNGR2, causing an amino acid substitution in the extracellular region of the encoded receptor. Cell surface IFN-gammaR2 were detected by flow cytometry. Cellular responses to IFN-gamma were impaired but not abolished. Transfection with the wild-type IFNGR2 gene restored full responsiveness to IFN-gamma. This is the first demonstration of partial IFN-gammaR2 deficiency in humans.

Growth of Mycobacterium bovis, Bacille Calmette-Guérin, within human monocytes-macrophages cultured in serum-free medium

Mycobacterium bovis BCG is an opportunistic agent that may be responsible for disseminated disease in immunocompromised individuals. Under physiological conditions, macrophages are the natural hosts and final killers of BCG. In the context of inherited or acquired immune disorders underlying disseminated BCG infections, macrophages fail to eradicate BCG or even to restrict its intracellular growth. The direct contribution of macrophages, in this setting of impaired BCG destruction, probably depends on the type of underlying immune deficiency and remains to be experimentally investigated. As an initial approach, we document here the fate of BCG within human monocytes and human monocyte-derived macrophages (MDMs) cultured in commercially available serum-free medium (M-SFM). This medium was used to avoid potential problems associated with human or animal serum-supplemented medium. We show here that both monocytes and MDMs cultured in M-SFM display the morphological features and functional activities expected for such cells. We also show that after an initial phase of intracellular destruction, BCG grow within infected monocytes-macrophages, as shown by colony forming unit (CFU) counts and Ziehl-Nielsen staining. By an electron microscopic analysis, we show that the BCG always reside within phagosomes and that 24-h postinfection many phagosomes stain for the hydrolytic enzyme acid phosphatase. Finally, we compare bacterial growth in vitro within phagocytes from healthy individuals and patients with chronic granulomatous disease (CGD), an inheritable condition associated with disseminated BCG infection in vivo. No destruction of intracellular BCG was achieved by the patients cells, revealing the essential mycobactericidal role of the respiratory burst in human phagocytes. Investigations of BCG growth within MDM cultured in M-SFM from patients with other conditions which predispose to clinical BCG infection is therefore warranted.

A human IFNGR1 small deletion hotspot associated with dominant susceptibility to mycobacterial infection

The immunogenetic basis of severe infections caused by bacille Calmette-Guérin vaccine and environmental mycobacteria in humans remains largely unknown. We describe 18 patients from several generations of 12 unrelated families who were heterozygous for 1 to 5 overlapping IFNGR1 frameshift small deletions and a wild-type IFNGR1 allele. There were 12 independent mutation events at a single mutation site, defining a small deletion hotspot. Neighbouring sequence analysis favours a small deletion model of slipped mispairing events during replication. The mutant alleles encode cell-surface IFNgamma receptors that lack the intra-cytoplasmic domain, which, through a combination of impaired recycling, abrogated signalling and normal binding to IFNgamma exert a dominant-negative effect. We thus report a hotspot for human IFNGR1 small deletions that confer dominant susceptibility to infections caused by poorly virulent mycobacteria.

Partial interferon-gamma receptor 1 deficiency in a child with tuberculoid bacillus Calmette-Guérin infection and a sibling with clinical tuberculosis

Complete interferon-gamma receptor 1 (IFNgammaR1) deficiency has been identified previously as a cause of fatal bacillus Calmette-Guérin (BCG) infection with lepromatoid granulomas, and of disseminated nontuberculous mycobacterial (NTM) infection in children who had not been inoculated with BCG. We report here a kindred with partial IFNgammaR1 deficiency: one child afflicted by disseminated BCG infection with tuberculoid granulomas, and a sibling, who had not been inoculated previously with BCG, with clinical tuberculosis. Both responded to antimicrobials and are currently well without prophylactic therapy. Impaired response to IFN-gamma was documented in B cells by signal transducer and activator of transcription 1 nuclear translocation, in fibroblasts by cell surface HLA class II induction, and in monocytes by cell surface CD64 induction and TNF-alpha secretion. Whereas cells from healthy children responded to even low IFN-gamma concentrations (10 IU/ml), and cells from a child with complete IFNgammaR1 deficiency did not respond to even high IFN-gamma concentrations (10,000 IU/ml), cells from the two siblings did not respond to low or intermediate concentrations, yet responded to high IFN-gamma concentrations. A homozygous missense IFNgR1 mutation was identified, and its pathogenic role was ascertained by molecular complementation. Thus, whereas complete IFNgammaR1 deficiency in previously identified kindreds caused fatal lepromatoid BCG infection and disseminated NTM infection, partial IFNgammaR1 deficiency in this kindred caused curable tuberculoid BCG infection and clinical tuberculosis.

Infections in IFNGR-1-deficient children

Human interferon-gamma receptor 1 (IFNGR-1) deficiency is a newly identified autosomal recessive inherited immune disorder. Children with IFNGR-1 deficiency exhibit a severe, profound and selective susceptibility to weakly virulent mycobacteria, such as bacillus Calmette-Guerin (BCG) vaccine or environmental nontuberculous mycobacteria (NTM). This review compares the infections found in IFNGR-1-deficient children to those in IFN-gamma-deficient or IFNGR-1-deficient mice.

Different patterns of HIV-1-specific cytotoxic T-lymphocyte activity after primary infection

OBJECTIVE

To analyse the HIV-1-specific cytotoxic T-lymphocyte (CTL) responses of nine HIV-seropositive subjects in relation with primary infection.

METHODS

Anti-HIV CTL were generated by in vitro stimulation of peripheral mononuclear cells obtained from HIV-seropositive donors at various times after primary infection. They were tested against several structural or regulatory HIV-1 proteins, using autologous target cells infected with recombinant vaccinia viruses expressing one of the HIV-1LAI proteins.

RESULTS

An important CTL activity was found during the first month following seroconversion only in those donors who showed clinical symptoms during primary infection. The temporal evolution of this response differed for each subject; one remained a non-responder even 30 months after seroconversion. The structural proteins were recognized particularly early, while the antigenicity of regulatory proteins appeared later.

CONCLUSION

Different patterns of HIV-specific CTL response can be observed after primary infection. The evolution of infection in these different HIV-seropositive subjects will be particularly interesting to analyse.

Identification of multirestricted immunodominant regions recognized by cytolytic T lymphocytes in the human immunodeficiency virus type 1 Nef protein

Peripheral blood mononuclear cells from a large number of human immunodeficiency virus (HIV)-seropositive donors were used to analyze the CD8+ T-cell response to each part of the Nef protein of HIV-1/LAI. This report identifies an immunodominant region (amino acids 73 to 144) in the Nef protein that was recognized by 97% of the NEF responder donors. This peptide sequence was dissected into four epitopic regions (amino acids 73 to 82, 83 to 97, 113 to 128, and 126 to 144), each of which was recognized under different HLA class I restrictions. Short overlapping peptides were used to sensitive the target cells for cytolysis and so to determine if these epitopic regions were multirestricted. Each region was found to contain several epitopes recognized with different HLA molecules. Thus, the central region of the Nef protein, a regulatory protein expressed early in HIV-infected cells, is rich in epitopic sequences which are found to be similar in many infected individuals and which can be recognized in association with at least ten HLA class I molecules. Their implications for the vaccination of humans with peptide sequences are discussed.

Qualitative and quantitative analysis of human cytotoxic T-lymphocyte responses to HIV-1 proteins

OBJECTIVE

To study the degree of immunogenicity of each HIV-1 protein.

DESIGN

In most viral systems, antiviral cytotoxic T-lymphocytes (CTL) from a given donor preferentially recognize only one or a small number of viral proteins.

METHODS

Anti-HIV CTL were generated by in vitro stimulation of peripheral blood mononuclear cells from seropositive donors and tested against multiple HIV-1 proteins or groups of proteins encoded by seven genes (env, gag, pol, nef, rev, tat and vif). Using autologous target cells infected with recombinant vaccinia viruses expressing one of the HIV-1LAI proteins, we compared the cytolytic activities obtained from bulk culture with those found in limiting dilution analysis (LDA).

RESULTS

Our results were noteworthy for the following reasons. (1) Each responding donor reacted simultaneously to multiple proteins; this is very unusual in other viral systems. Anti-Gag CTL were detected in most, and anti-Pol in approximately three-quarters, of the patients, together with very high amounts of the corresponding CTL precursors in LDA. CTL against Env and Nef were found in two-thirds of the patients, while Vif- and Rev-specific CTL were less frequent. Finally, Tat was seldom recognized by CTL, but its antigenicity was revealed in LDA. (2) All responding cells revealed in bulk cultures as well as in LDA were CD8+ T-cells, and their in vitro differentiation did not require the help of CD4+ T-cells. (3) Proteins from the HIV-1LAI isolate were recognized with high frequency by CTL from seropositive donors, most certainly being infected by other isolates, which suggests that relatively conserved epitopes are predominant targets of CTL.

CONCLUSION

Taken together, these results are encouraging for vaccine purposes, since anti-HIV-1 CTL stimulation is thought to be a requirement for such a vaccine.