IgG subclass deficiencies in children: Facts and fiction.

The chance to analyse the four IgG subclasses arose with the publication of Terry and Fahey1 . Since then, a lot of new information on the role of subclasses and their deficiency states in humans has been obtained. This review tries to analyse critically our current knowledge of subclass deficiencies in children.

Basic science for the clinician 58: IgG subclasses.

In evolutionary terms, IgG is the most recent addition to the human humoral immune response, the most recent of the 5 isotypes (classes). The IgG 4 subclasses and their multiple receptors, each with a unique structure and functions, speak to their broad repertoire of often overlapping functions. The IgG subclasses differ only slightly in structure, but therein lies their unique qualities. Focusing solely on the clinical niches filled by each and the clinical correlations thereof allows one to clearly see nature in its abhorrence of, and skill in filling, vacuums. One of the IgG subclasses, IgG4, the least in serum concentration, has recently become the topic of intense interest, as the linkage of certain diseases with IgG4 becomes apparent. As this association is studied, the molecular biology at the root of these diseases becomes the predominant cytokines explaining the pattern of histopathology.

Immunoglobulin G subclass deficiency is the major phenotype of primary immunodeficiency in a Korean adult cohort.

Primary immunodeficiency disease (PID) is a rare disorder in adults. Most often, serious forms are detected during infancy or childhood. However, mild forms of PID may not be diagnosed until later in life, and some types of humoral immunodeficiency may occur in adulthood. The purpose of this study was to identify clinical features of PID in Korean adults. A retrospective study was performed on 55 adult patients who were diagnosed as PID between January 1998 and January 2009 at a single tertiary medical center in Korea. IgG subclass deficiency was the most common phenotype (67%, 37/55), followed by total IgG deficiency (20%, 11/55), IgM deficiency (7%, 4/55), common variable immunodeficiency (2%, 1/55), and X-linked agammaglobulinemia (2%, 1/55). IgG3 and IgG4 were the most affected subclasses. Upper and lower respiratory tract infections (76%) were the most frequently observed symptoms, followed by multiple site infection (11%), urinary tract infection, and colitis. Bronchial asthma, rhinitis, and several autoimmune diseases were common associated diseases. IgG and IgG subclass deficiency should be considered in adult patients presenting with recurrent upper and lower respiratory infections, particularly in those with respiratory allergies or autoimmune diseases.

IgA deficiency: correlation between clinical and immunological phenotypes.

BACKGROUND: IgA deficiency (IGAD) is the most common primary antibody deficiency. Although many affected individuals have no apparent symptom, selected patients suffer from recurrent mucosal infections, allergies, and autoimmune diseases. We aimed to investigate the clinical features in relation to immune function of Iranian patients with symptomatic IGAD. METHODS: Thirty-seven patients (21 male and 16 female), aged 4-32 years, were evaluated in this study. Patients were followed for a total of 131 patient years with a mean follow-up of 3.5 years per patient. RESULTS: The most prevalent presentations were recurrent infections occurring in 27 subjects, followed by allergy in eight cases and autoimmunity in two patients. However, during the follow-up period, 35 patients developed infections in respiratory and gastrointestinal tracts, necessitating medical care. Apart from infections, allergy was the most frequent complaint (31 cases); the major features were asthma, atopic dermatitis, and allergic rhinoconjunctivitis. Autoimmune diseases were documented in ten cases; thyroiditis was the most common. In 31 patients who received unconjugated pneumococcal polyvalent vaccine, antibody response against polysaccharide antigen was measured before and 28 days after vaccination. One fourth of vaccinated patients were hyporesponsive to vaccine; four of these patients developed bronchiectasis. The patients with IGAD were classified into two groups: group 1 (14 cases) consisted of patients with IGAD and other associated immune defects, such as immunoglobulin G (IgG) subclass deficiency and defective specific antibody production. Group 2 (23 cases) had isolated IGAD without other immunological abnormalities. There was a significantly increased number of lower respiratory tract infections in group 1 compared with group 2 (P = 0.006). Moreover, four patients of group 1 had bronchiectasis whereas none of the patients in group 2 developed this complication (P = 0.015). CONCLUSION: Subclassification of IGAD regarding the existence of associated immune defects is useful in terms of morbidity and planning for medical care. IgA-deficient patients with concomitant immune defects such as defects in specific antibody production have higher rates of recurrent infections and bronchiectasis, which necessitates more effective monitoring.

Chronic glomerulonephritis associated with IgG subclass deficiency.

We experienced two patients with IgG subclass deficiency who suffered from chronic glomerulonephritis (GN). Patient 1 was a 17-year-old girl with IgG subclass deficiency (combined deficiency of IgG2 and IgG4). Renal biopsy was performed when she was aged 16 years, and she was diagnosed with membranoproliferative GN. Patient 2 was a 16-year-old girl with IgG subclass deficiency (combined deficiency of IgG2, IgG3, and IgG4). Renal biopsy was performed when she was aged 15 years, and she was diagnosed with membranous nephropathy. We examined the glomerular deposition patterns of their IgG subclasses. Furthermore, we compared their clinical and laboratory findings with those of three patients with IgG subclass deficiency without GN. Patients with GN suffered infections more frequently than those without GN. The serum levels of IgG (especially IgG1) and IgM were higher in patients with GN than in those without GN. In patient 1 IgG1 and IgG3 were deposited in a mesangiocapillary pattern, but, in patient 2, only IgG1 was deposited in a capillary pattern. Thus, the different patterns of IgG subclass deficiency between the two patients may be responsible for their different glomerular pathologies. To the best of our knowledge, this is the first report of chronic GN in patients with IgG subclass deficiency.

A case of IgG subclass deficiency with the initial presentation of transient hypogammaimmuno-globulinemia of infancy and a review of IgG subclass deficiencies.

UNLABELLED: Primary immunodeficiency diseases are not common in children. The possibility of an immunological defect should be considered in any individual with repeated infections. A definite diagnosis for immodeficiency is sometimes difficult to achieve because of overlapping clinical manifestations. Immunoglobulin subclass deficiency is an immunological deficiency disease with which, one or more IgG subclasses are deficient. T cell immunity is normal. Patients may develop recurrent bacterial and respiratory infections or could remain asymptomatic. OBJECTIVE: The authors report a case of immunoglobulin G subclass deficiency presenting initially as transient hypogammaglobulinemia of infancy. CASE REPORT: A 2 month-old boy presented to Siriraj Hospital with a history of chronic protracted diarrhea, disseminated scabies and sepsis. On presentation, he had generalized scaly and maculopapular rash with no palpable lymph nodes. CBC revealed WBC 22,100 cells/cm3 with PMN 42 per cent, lymphocytes 38 per cent, Eosinophils 4 per cent, Basophil 2 per cent and platelets 254,000/cm3. The immunoglobulin levels were as follows: IgG 181 mg/dl, IgA < 6.6 mg/dl, IgM 26.3 mg/dl. Lymphocyte enumerations revealed CD4 of 2,433 cells/cm3 (N 1,460-5,160); CD8 4,682 cells/cm3 (N 650-2,450); CD19 1,588 cell/cm3 (N 500-1,500); CD16 230 cell/cm3 (N 573 +/- 264). The initial diagnosis was X-linked agammaglobulinemia vs common variable immunodeficiency disease. His diarrhea and five courses of sepsis responded well to antibiotics administration and courses of intravenous immunoglobulin (IVIG) replacement. His through IgG became normal at 2 years of age (after 12 months of IVIG). IVIG was stopped and the diagnosis was changed to transient hypogammaglobulinemia of infancy (THI). Nevertheless, during his 4 month follow-up he developed recurrent sinopulmonary infections (i.e, otitis media and pneumonia). Repeated immunoglobulin profile showed IgG 1,200 mg/dl, IgA 135 mg/dl, IgM 26 mg/dl, IgG subclass were IgG, 1,030 mg/dl (N 280-830), IgG2 30 mg/dl (N 40-2,400), IgG3 22 mg/dl (N 6-130), IgG4 3 mg/dl (N 3-120). A diagnosis of IgG2 subclass deficiency presenting early as transient hypogammaglobulinemia of infancy was then made. Treatment with monthly IVIG was reinitiated and the patient is currently doing well. CONCLUSION: The authors present a case of IgG subclass deficiency presenting as transient hypogammaglbulinemia of infancy. Follow-up of the immune profile and clinical manifestation is necessary for a definite diagnosis.

Evaluation of the relevance of humoral immunodeficiencies in a pediatric population affected by recurrent infections.

Recurrent infections are a common cause of morbidity in childhood. Several reports have associated this condition to low levels of IgA and IgG subclasses and/or lack of specific antipolysaccharide antibody response, although the relevance of these defects in terms of prognosis and therapeutic approach is still unclear. The aim of our study was to determine the frequency and the clinical relevance of humoral immunodeficiency (HID) other than hypogammaglobulinemia in children affected by recurrent infections. We recruited 67 pediatric patients affected by recurrent infections. Serum IgG, IgA, IgM, IgG2, IgG3, and specific anti-Haemophilus influenzae (anti-Hib) antibodies were determined. Thirty-seven out of 67 patients showed antibody defects (55%). IgA deficiency was observed in 21 out of 67 patients (31%), followed by IgG2 (18%), IgG3 (15%) and IgM (6%) defects. Anti-Hib deficiency was present in three out of 44 patients (7%). A tendency for a higher occurrence of pneumonia and otitis, although not statistically significant (p > 0.05), was observed in HID patients compared to children with normal humoral function. No statistical difference as to the frequency of mild infections (URI) was found between HID and non-HID patients. We therefore suggest that the therapeutic program is based on the clinical status of the patients. Long-term follow-up with repeated determinations of antibody levels is crucial, however, to detect those defects that might evolve into more complex immunodeficiencies.

Molecular analysis of the T17 immunoglobulin CH multigene deletion (del A1-GP-G2-G4-E).

In the human, the order of the immunoglobulin heavy chain constant region (Ig CH) genes is the following: 5'-M-D-G3-G1-EP1-A1-GP-G2-G4-E-A2-3'. Extensive multigene deletions have been described in the Ig CH locus, some of these encompassing up to 160 kb. To date six different multigene deletion haplotypes have been identified, designated I to VI according to the chronological order of their being found: deletion I (del G1-EP1-A1-GP-G2-G4), II (del EP1-A1-GP), III (del A1-GP-G2-G4-E), IV (del EP1-A1-GP-G2-G4), V (del GP-G2-G4-E-A2), VI (del G1-EP1-A1-GP-G2). Individuals were found either homozygous for one type of deletion or heterozygous for two different deletions, mainly (17 cases out of 18) in the Mediterranean area. So far, deletions I and II have been found in Tunisia, deletions III, IV and V in Italy, and deletion VI in Sweden. In this paper, we show that a Tunisian, T17, previously reported as being homozygous for a deletion of type IV, is, in fact, homozygous for a deletion that encompasses A1-GP-G2-G4-E. Therefore T17 is the first case of a deletion of type III reported in the Tunisian population. Molecular analysis demonstrates that the T17 deletion occurred between highly homologous regions located downstream of IGHEP1 and IGHE, respectively. In contrast to the EZZ deletion, the recombination occurred near or in the switch regions, since the homologous regions involved in the deletion extend over 4.5 kb of DNA and encompass the I alpha 1-S alpha 1 and I alpha 2-S alpha 2 regions, respectively.

Normal levels of IgG subclass in childhood determined by a sensitive ELISA.

Normal values of all IgG subclasses were determined using a sensitive ELISA in children aged from newborn to 14 years. The upper and lower limits of normal values of all IgG subclasses were obtained in all the age groups using 29 umbilical cord blood samples from full-term newborns and 308 venous blood samples from normal infants and children. The trends in the levels of IgG1, IgG2 and IgG3 with age were almost similar to previous reports. IgG4 levels decreased gradually until reaching the lowest level at 7 to 12 months and increased gradually with age, reaching a plateau at 12 to 14 years of age. Thus, the lower limit of serum IgG4 levels was determined using our method.