Asunto(s)
Síndrome de Inmunodeficiencia con Hiper-IgM/enzimología , Síndrome de Inmunodeficiencia con Hiper-IgM/inmunología , Células Asesinas Naturales/enzimología , Células Asesinas Naturales/inmunología , Fosfatidilinositol 3-Quinasas/metabolismo , Estudios de Casos y Controles , Degranulación de la Célula , Fosfatidilinositol 3-Quinasa Clase Ia , Citotoxicidad Inmunológica , Humanos , Síndrome de Inmunodeficiencia con Hiper-IgM/genética , Interferón gamma/biosíntesis , Células K562 , Mutación , Fosfatidilinositol 3-Quinasas/genética , Transducción de SeñalRESUMEN
The hyper-immunoglobulin M (HIGM) syndrome is a heterogeneous group of genetic disorders characterized by recurrent infections, decreased serum levels of immunoglobulin G (IgG) and IgA, and normal/increased serum levels of IgM. Herein, we describe three Turkish siblings with HIGM syndrome who had a homozygous missense mutation (c.70C>T, p.Arg24Trp) in the activation-induced cytidine deaminase gene which results in autosomal recessive HIGM syndrome. Two of the siblings, sibling 1 and sibling 3, presented with cervical deep abscess and cervical tuberculosis lymphadenitis, respectively.
Asunto(s)
Citidina Desaminasa/genética , Síndrome de Inmunodeficiencia con Hiper-IgM/enzimología , Linfadenitis/etiología , Tuberculosis/etiología , Adolescente , Niño , Citidina Desaminasa/metabolismo , Femenino , Genes Recesivos , Humanos , Síndrome de Inmunodeficiencia con Hiper-IgM/sangre , Síndrome de Inmunodeficiencia con Hiper-IgM/complicaciones , Síndrome de Inmunodeficiencia con Hiper-IgM/genética , Inmunoglobulina A/sangre , Inmunoglobulina G/sangre , Inmunoglobulina M/sangre , Linfadenitis/sangre , Masculino , Mutación Missense , Hermanos , Tuberculosis/sangre , TurquíaRESUMEN
Hyper-IgM syndrome type 2 stems from mutations in activation-induced deoxycytidine deaminase (AID) that abolish immunoglobulin class-switch recombination, causing an accumulation of IgM and absence of IgG, IgA, and IgE isotypes. Although hyper-IgM syndrome type 2 is rare, the 23 missense mutations identified in humans span almost the entire gene for AID resulting in a recessive phenotype. Using high resolution x-ray structures for Apo3G-CD2 as a surrogate for AID, we identify three classes of missense mutants as follows: catalysis (class I), substrate interaction (class II), and structural integrity (class III). Each mutant was expressed and purified from insect cells and compared biochemically to wild type (WT) AID. Four point mutants retained catalytic activity at 1/3rd to 1/200th the level of WT AID. These "active" point mutants mimic the behavior of WT AID for motif recognition specificity, deamination spectra, and high deamination processivity. We constructed a series of C-terminal deletion mutants (class IV) that retain catalytic activity and processivity for deletions ≤18 amino acids, with ΔC(10) and ΔC(15) having 2-3-fold higher specific activities than WT AID. Deleting 19 C-terminal amino acids inactivates AID. WT AID and active and inactive point mutants bind cooperatively to single-stranded DNA (Hill coefficients â¼1.7-3.2) with microscopic dissociation constant values (K(A)) ranging between 10 and 250 nm. Active C-terminal deletion mutants bind single-stranded DNA noncooperatively with K(A) values similar to wild type AID. A structural analysis is presented that shows how localized defects in different regions of AID can contribute to loss of catalytic function.
Asunto(s)
Citidina Desaminasa , ADN de Cadena Simple , Síndrome de Inmunodeficiencia con Hiper-IgM , Cambio de Clase de Inmunoglobulina , Mutación Missense , Mutación Puntual , Eliminación de Secuencia , Secuencia de Aminoácidos , Antígenos CD2/química , Antígenos CD2/genética , Antígenos CD2/metabolismo , Catálisis , Citidina Desaminasa/química , Citidina Desaminasa/genética , Citidina Desaminasa/metabolismo , Humanos , Síndrome de Inmunodeficiencia con Hiper-IgM/enzimología , Síndrome de Inmunodeficiencia con Hiper-IgM/genética , Inmunoglobulina M , Unión Proteica , Estructura Terciaria de Proteína , Relación Estructura-ActividadRESUMEN
Somatic hypermutation normally occurs as a consequence of the expression of activation-induced cytidine deaminase (AID) by Ag-activated, mature B cells during T cell-dependent germinal center responses. Nonetheless, despite their inability to express CD154 and initiate GC responses, patients with type 1 hyper-IgM syndrome (HIGM1) support populations of IgM(+)IgD(+)CD27(+) B cells that express mutated Ig genes. The origin of these mutated B cells is unknown; the IgM(+)IgD(+)CD27(+) cells do not express AID and appear to acquire mutations independent of stringent selection by Ag. Here, we demonstrate that immature/transitional 1 B cells from the bone marrow of CD154-deficient mice express AID and acquire Ig mutations that lack the hallmarks of antigenic selection via BCR signaling. Comparable levels of AID expression was found in developmentally immature B cells recovered from murine fetal liver and from human immature/transitional 1 B cells recovered from umbilical cord blood. AID expression in human fetal liver was also robust, approaching that of human tonsil tissue and the human germinal center B cell line, Ramos. These observations led us to conclude that AID expression in developing human B cells is the origin of the mutated IgM(+)IgD(+)CD27(+) B cells present in HIGM1 patients, and we propose that both mice and humans share a latent, AID-dependent pathway for the preimmune diversification of B lymphocytes that is more prominent in chicken, sheep, and rabbits.
Asunto(s)
Citidina Desaminasa/genética , Citidina Desaminasa/metabolismo , Centro Germinal/inmunología , Centro Germinal/patología , Síndrome de Inmunodeficiencia con Hiper-IgM/enzimología , Síndrome de Inmunodeficiencia con Hiper-IgM/inmunología , Animales , Subgrupos de Linfocitos B/enzimología , Subgrupos de Linfocitos B/inmunología , Subgrupos de Linfocitos B/patología , Células de la Médula Ósea/enzimología , Células de la Médula Ósea/inmunología , Células de la Médula Ósea/patología , Línea Celular Transformada , Línea Celular Tumoral , Citidina Desaminasa/biosíntesis , Femenino , Regulación del Desarrollo de la Expresión Génica/inmunología , Reordenamiento Génico de Linfocito B/genética , Centro Germinal/enzimología , Humanos , Síndrome de Inmunodeficiencia con Hiper-IgM/genética , Inmunofenotipificación , Activación de Linfocitos/genética , Activación de Linfocitos/inmunología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Datos de Secuencia Molecular , Receptores de Antígenos de Linfocitos B/deficiencia , Receptores de Antígenos de Linfocitos B/genética , Transducción de Señal/genética , Transducción de Señal/inmunología , Hipermutación Somática de Inmunoglobulina/genética , Células Madre/enzimología , Células Madre/inmunología , Células Madre/patologíaRESUMEN
OBJECTIVES: We aimed to investigate the activity of ADA and its isoenzymes in serum of patients with various primary immunodeficiency (PID) syndromes. DESIGN AND METHODS: Total ADA (tADA) and its isoenzymes were measured in 76 children with PID syndromes and 30 healthy controls using the Ellis method. RESULTS: Our results indicated that tADA and ADA2 levels were higher in patients with Chronic Granulomatous Disease (CGD), Leukocyte Adhesion Deficiency (LAD), hyper IgM (HIM) and Wiskott-Aldrich Syndrome (WAS) than those of corresponding controls (P<0.01). There was a significant elevation of tADA and ADA1 activities in IgA deficiency patients as compared to healthy individuals (P<0.01). CONCLUSIONS: Our results hypothesized that altered ADA activity may be associated with altered immunity. Therefore, serum ADA level could be used as an indicator along with other parameters in follow up of patients with CGD, LAD, IgA deficiency, HIM and WAS.
Asunto(s)
Adenosina Desaminasa/sangre , Inmunodeficiencia Combinada Grave/enzimología , Adenosina Desaminasa/metabolismo , Adolescente , Análisis de Varianza , Niño , Preescolar , Enfermedad Granulomatosa Crónica/enzimología , Humanos , Síndrome de Inmunodeficiencia con Hiper-IgM/enzimología , Deficiencia de IgA/enzimología , Deficiencia de IgG/enzimología , Lactante , Irán , Isoenzimas/sangre , Isoenzimas/metabolismo , Síndrome de Deficiencia de Adhesión del Leucocito/enzimología , Inmunodeficiencia Combinada Grave/patologíaRESUMEN
APOBEC-2 (APO2) belongs to the family of apolipoprotein B messenger RNA-editing enzyme catalytic (APOBEC) polypeptides, which deaminates mRNA and single-stranded DNA. Different APOBEC members use the same deamination activity to achieve diverse human biological functions. Deamination by an APOBEC protein called activation-induced cytidine deaminase (AID) is critical for generating high-affinity antibodies, and deamination by APOBEC-3 proteins can inhibit retrotransposons and the replication of retroviruses such as human immunodeficiency virus and hepatitis B virus. Here we report the crystal structure of APO2. APO2 forms a rod-shaped tetramer that differs markedly from the square-shaped tetramer of the free nucleotide cytidine deaminase, with which APOBEC proteins share considerable sequence homology. In APO2, two long alpha-helices of a monomer structure prevent the formation of a square-shaped tetramer and facilitate formation of the rod-shaped tetramer via head-to-head interactions of two APO2 dimers. Extensive sequence homology among APOBEC family members allows us to test APO2 structure-based predictions using AID. We show that AID deamination activity is impaired by mutations predicted to interfere with oligomerization and substrate access. The structure suggests how mutations in patients with hyper-IgM-2 syndrome inactivate AID, resulting in defective antibody maturation.