Diversification, not use, of the immunoglobulin VH gene repertoire is restricted in DiGeorge syndrome

B-cell receptor repertoire sequencing in patients with primary immunodeficiency: a review

The advent of next-generation sequencing (NGS) now allows a detailed assessment of the adaptive immune system in health and disease. In particular, high-throughput B-cell receptor (BCR) repertoire sequencing provides detailed information about the functionality and abnormalities of the B-cell system. However, it is mostly unknown how the BCR repertoire is altered in the context of primary immunodeficiencies (PID) and whether findings are consistent throughout phenotypes and genotypes. We have performed an extensive literature search of the published work on BCR repertoire sequencing in PID patients, including several forms of predominantly antibody disorders and combined immunodeficiencies. It is somewhat surprising that BCR repertoires, even from severe clinical phenotypes, often show only mild abnormalities and that diversity or immunoglobulin gene segment usage is generally preserved to some extent. Despite the great variety of wet laboratory and analytical methods that were used in the different studies, several findings are common to most investigated PIDs, such as the increased usage of gene segments that are associated with self-reactivity. These findings suggest that BCR repertoire characteristics may be used to assess the functionality of the B-cell compartment irrespective of the underlying defect. With the use of NGS approaches, there is now the opportunity to apply BCR repertoire sequencing to multiple patients and explore the PID BCR repertoire in more detail. Ultimately, using BCR repertoire sequencing in translational research could aid the management of PID patients by improving diagnosis, estimating functionality of the immune system and improving assessment of prognosis.

Immunodeficiency in DiGeorge Syndrome and Options for Treating Cases with Complete Athymia

The commonest association of thymic stromal deficiency resulting in T-cell immunodeficiency is the DiGeorge syndrome (DGS). This results from abnormal development of the third and fourth pharyngeal arches and is most commonly associated with a microdeletion at chromosome 22q11 though other genetic and non-genetic causes have been described. The immunological competence of affected individuals is highly variable, ranging from normal to a severe combined immunodeficiency when there is complete athymia. In the most severe group, correction of the immunodeficiency can be achieved using thymus allografts which can support thymopoiesis even in the absence of donor-recipient matching at the major histocompatibility loci. This review focuses on the causes of DGS, the immunological features of the disorder, and the approaches to correction of the immunodeficiency including the use of thymus transplantation.

Immunological aspects of 22q11.2 deletion syndrome

Chromosome 22q11 deletion is the most common chromosomal deletion syndrome and is found in the majority of patients with DiGeorge syndrome and velo-cardio-facial syndrome. Patients with CHARGE syndrome may share similar features. Cardiac malformations, speech delay, and immunodeficiency are the most common manifestations. The immunological phenotype may vary widely between patients. Severe T lymphocyte immunodeficiency is rare-thymic transplantation offers a new approach to treatment, as well as insights into thymic physiology and central tolerance. Combined partial immunodeficiency is more common, leading to recurrent sinopulmonary infection in early childhood. Autoimmunity is an increasingly recognized complication. New insights into pathophysiology are reviewed.

Secondary immunologic consequences in chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

Clinical evidence suggests that patients with Chromosome 22q11.2 deletion (Ch22q11.2D) have an increased prevalence of atopic and autoimmune disease and this has been without explanation. We hypothesized that the increase in atopy was due to homeostatic proliferation of T cells leading to a Th2 skew. We performed intracellular cytokine staining to define Th1/Th2 phenotypes in toddlers (early homeostatic proliferation) and adults (post homeostatic proliferation) with this syndrome. To attempt to understand the predisposition to autoimmunity we performed immunophenotyping analyses to define Th17 cells and B cell subsets. Adult Ch22q11.2D patients had a higher percentage of IL-4+CD4+ T cells than controls. Th17 cells were no different in patients and controls. In addition, adult Ch22q11.2D syndrome patients had significantly lower switched memory B cells, suggesting a dysregulated B cell compartment. These studies demonstrate that the decrement in T cell production has secondary consequences in the immune system, which could mold the patients' clinical picture.

Isolation and identification of an scFv antibody against nucleocapsid protein of SARS-CoV

To develop reagents for early diagnosis and therapeutic drugs against SARS-associated coronavirus (SARS-CoV), a large (3 × 10⁹) immunized human antibody library was constructed from peripheral blood mononuclear cells from six SARS convalescent patients. A single chain variable fragment antibody (N18) with high affinity against N protein of SARS-CoV was isolated. Sequence analysis revealed that the VL gene was composed of VL3 h (V lambda subgroup) and JL2 regions and the VH gene was composed of VH1-69 (VH1 subgroup), D2-15, D3-22 and JH6 regions. Soluble N18 antibody was expressed in Escherichia coli HB2151, purified by Ni–NTA affinity chromatography and verified by SDS-PAGE and Western blot. The potential application for early diagnosis was evaluated using N protein capture ELISA in which N18 antibody demonstrated high sensitive activity in detecting N protein of SARS-CoV. Finally, the potential usefulness of the N18 antibody in prophylaxis, vaccine design and therapy of SARS is discussed.

Complex expression patterns of lymphocyte-specific genes during the development of cartilaginous fish implicate unique lymphoid tissues in generating an immune repertoire

Cartilaginous fish express canonical B and T cell recognition genes, but their lymphoid organs and lymphocyte development have been poorly defined. Here, the expression of Ig, TCR, recombination-activating gene (Rag)-1 and terminal deoxynucleosidase (TdT) genes has been used to identify roles of various lymphoid tissues throughout development in the cartilaginous fish, Raja eglanteria (clearnose skate). In embryogenesis, Ig and TCR genes are sharply up-regulated at 8 weeks of development. At this stage TCR and TdT expression is limited to the thymus; later, TCR gene expression appears in peripheral sites in hatchlings and adults, suggesting that the thymus is a source of T cells as in mammals. B cell gene expression indicates more complex roles for the spleen and two special organs of cartilaginous fish-the Leydig and epigonal (gonad-associated) organs. In the adult, the Leydig organ is the site of the highest IgM and IgX expression. However, the spleen is the first site of IgM expression, while IgX is expressed first in gonad, liver, Leydig and even thymus. Distinctive spatiotemporal patterns of Ig light chain gene expression also are seen. A subset of Ig genes is pre-rearranged in the germline of the cartilaginous fish, making expression possible without rearrangement. To assess whether this allows differential developmental regulation, IgM and IgX heavy chain cDNA sequences from specific tissues and developmental stages have been compared with known germline-joined genomic sequences. Both non-productively rearranged genes and germline-joined genes are transcribed in the embryo and hatchling, but not in the adult.

The DiGeorge anomaly

The DiGeorge anomaly, originally considered a clinical paradigm for isolated thymus deficiency, has now been redefined as a member of a group of disorders that share in common a chromosome deletion resulting in monosomy 22q11 (CATCH-22 or DGA/VCFS). In addition to the thymus defect, conotruncal heart anomalies, dysmorphism, hypoparathyroidism, and cleft palate are prominent features. Despite the emphasis on thymus involvement in DGA, a clinically significant thymus defect is found only in a small percentage of these patients probably occurring in less than 5% of the cases. Maldescent of the thymus, however, is extremely common, leading to an absence of mediastinal thymic tissue in nearly all cases. The basic embryological fault in these disorders is an inadequate development of the facial neural-crest tissues, resulting in defective organogenesis of pharyngeal pouch derivatives that receive cephalic neural-crest contribution to the mesenchmyme. The causes for this maldevelopment are both genetic and extragenetic in origin and the genetic lesions act in concert with random environmental events to produce the ultimate clinical picture. The modern research approaches now available have cleared away most of the confusion clouding the clinical and theoretical aspects of DGA and related disorders, providing the clinician with useful landmarks to assess and treat these intriguing clinical challenges.

DiGeorge anomaly: a comparative study of the clinical and immunologic characteristics of patients positive and negative by fluorescence in situ hybridization

BACKGROUND

DiGeorge anomaly (DGA) is defined as a field defect characterized by dysmorphic facies, hypoparathyroidism, congenital heart defects, and a deficiency in cell-mediated immunity, usually associated with a microdeletion in chromosome 22q11.2. Data correlating clinical and genetic information, especially in terms of the extent of the immunodeficiency and infectious complications, are scant.

OBJECTIVE

The goal of this study was to define the severity of the immunodeficiency and infectious illnesses in DGA patients with characteristic clinical and genetic findings and compare them with a similar group of patients without a microdeletion in chromosome 22q11.2.

METHODS

A retrospective chart review of patients referred for evaluation of DGA to our immunology service from 1989 to 1995 was conducted. Clinical and immunologic data were collected from their initial evaluation. Patients meeting at least 3 of 4 of these criteria were considered to meet strict clinical diagnostic criteria for DGA, and the results of analysis for a microdeletion in chromosome 22q11.2 for each patient was noted.

RESULTS

Sixteen of the 22 patients meeting strict clinical criteria for DGA were available for analysis for the microdeletion at chromosome 22q.11.2. Of these, 13 (81%) were positive by fluorescence in situ hybridization (FISH); 9 of 13 (69%) had low CD3 numbers, 6 of 10 assayed (60%) had low thymulin levels; 10 of 13 (77%) had low CD4 numbers, and 10 of 12 (83%) had absent or small thymus glands. B cells were increased in 9 of 13 (69%) patients. Mitogen and antigen responses were normal in 6 of 7 (86%) patients tested. Eight of 13 (62%) had a history of increased frequency of infectious illnesses. All had recurrent respiratory infections, including sinusitis, otitis media, and pneumonia. Three of the 16 patients tested (19%) were FISH negative. Two of 3 (67%) had low CD3 and CD4 numbers. B cells were elevated in all patients. All had recurrent respiratory infections, low thymulin levels, and absent thymus glands.

CONCLUSIONS

Contrary to traditional descriptions, this group of clinically and genetically defined patients with DGA had a predominantly mild cell-mediated immunodeficiency syndrome usually associated with infections characteristic of humoral immunodeficiencies. The patients who were FISH positive did not differ significantly from those that were FISH negative in terms of clinical and immunologic findings or infectious complications.

Somatic hypermutation in T-independent and T-dependent immune responses to Haemophilus influenzae type b polysaccharide

Secondary immune responses to T-independent antigens are characterized by little or no affinity maturation, a phenomenon attributed to limited somatic hypermutation. In the human immune response to Haemophilus influenzae type b capsular polysaccharide, however, there are numerous differences between rearranged heavy chain variable region gene segments and candidate germline genes, irrespective of antigen presentation in a T-independent or T-dependent form. To determine the characteristics of somatic hypermutation in this response, we analyzed rearranged heavy chain variable region segments and associated 3' untranslated JH4-JH5 introns from monoclonal anti-Hib PS antibodies. Mutation of untranslated introns and heavy chain variable segments in both T-independent and T-dependent responses resembles that described in murine and unselected human immune responses. Although mutation is frequent in both T-independent and T-dependent anti-Hib PS responses, there is little evidence of antigen-driven selection, suggesting that ongoing pressure to conserve the variable segment germline configuration limits affinity maturation in this immune response.

Juvenile rheumatoid arthritis-like polyarthritis in chromosome 22q11.2 deletion syndrome (DiGeorge anomalad/velocardiofacial syndrome/conotruncal anomaly face syndrome)

OBJECTIVE

To investigate the association of polyarthritis and chromosome 22q11.2 deletions.

METHODS

Eighty patients with chromosome 22q11.2 deletion syndrome followed up at The Children's Hospital of Philadelphia were examined for evidence of arthropathy or arthritis. Patients with chromosome 22q11.2 deletion syndrome and polyarthritis underwent laboratory evaluations of immunologic function to determine the relationship of their immunodeficiency to the polyarthritis.

RESULTS

The prevalence of polyarthritis in patients with chromosome 22q11.2 deletion syndrome was markedly increased over the prevalence of polyarticular juvenile rheumatoid arthritis (JRA) in the general population. All 3 patients with polyarthritis had evidence of impaired T cell function. Two of the patients with polyarthritis also had IgA deficiency.

CONCLUSION

The chromosome 22q11.2 deletion syndrome represents a primary T cell disorder which can be associated with a JRA-like polyarthritis. All 3 patients with polyarthritis had evidence of more extensive immunoregulatory derangements than those typically seen in patients with chromosome 22q11.2 deletion, and these derangements may have predisposed to the development of polyarthritis.

alpha, beta, gamma, and delta T cell antigen receptor genes arose early in vertebrate phylogeny

A series of products were amplified using a PCR strategy based on short minimally degenerate primers and R. eglanteria (clearnose skate) spleen cDNA as template. These products were used as probes to select corresponding cDNAs from a spleen cDNA library. The cDNA sequences exhibit significant identity with prototypic (alpha, beta, gamma, and delta T cell antigen receptor (TCR) genes. Characterization of cDNAs reveals extensive variable region diversity, putative diversity segments, and varying degrees of junctional diversification. This demonstrates expression of both alpha/beta and gamma/delta TCR genes at an early level of vertebrate phylogeny and indicates that the three major known classes of rearranging antigen receptors were present in the common ancestor of the present-day jawed vertebrates.

Variable region usage in B cell deficient mice in a model of experimental herpes simplex virus retinitis

By using PCR, we have found previously that differences in T cell receptor alpha/beta chain variable region (TCR alpha/beta) gene expression in lymph nodes (LN) existed between susceptible and resistant mice following anterior chamber (AC) inoculation with herpes simplex virus (HSV). We now report and compare the immunoglobulin gene variable region (Ig VH) and the TCR V beta mRNA expression in normal congenic mice (BALB/c and C.B-17) and also in B cell modulated C.B-17 mice (B-). RNA prepared from spleen and LN of these mice before and after HSV-AC inoculation was analysed by PCR using oligoprimers specific for 11 VH gene families and 19 V beta gene families. Densitometry analysis revealed that VH family mRNA expression levels in spleen and lymph nodes did not correlate with HSV susceptibility or resistance patterns in B-, BALB/c and C.B-17 mice. Analysis of TCR V beta chain genes showed that spleen of resistant C.B-17 and B-Ab transferred mice showed a preference for V beta 11 gene expression not seen in susceptible mice. In contrast, LN of BALB/c and B-, both susceptible mice, made TCR V beta transcripts that were indistinguishable from those generated by resistant C.B-17 mice, following HSV-AC inoculation. Finally, TCR V beta gene family repertoire appears to be severely diminished in uninfected B- mice (50% in LN and 45% in spleen) by anti-mu treatment.

Humoral immunity in DiGeorge syndrome

OBJECTIVE

To assess humoral immunity after immunization and natural infection in patients with clinical manifestations of the DiGeorge anomalad.

DESIGN

Retrospective review of cases.

SETTING

Ambulatory immunology clinic of a tertiary care teaching hospital.

PATIENTS

The 13 patients had a symptom complex including congenital heart disease, characteristic facies of the DiGeorge anomalad, possible hypocalcemia, and thymic hypoplasia or aplasia. Molecular and cytogenic studies of 12 patients demonstrated that all had 22q11 microdeletions.

METHODS

Serial studies included lymphocyte population enumeration by flow cytometry, lymphocyte proliferation assays with the mitogens phytohemagglutinin and pokeweed mitogen and Staphylococcus aureus, and immunoglobulin quantitation. Specific antibody studies included virus neutralization assays for poliovirus antibodies, and enzyme-linked immunosorbent assay for diphtheria, tetanus, measles, rubella, varicella-zoster virus (VZV), and cytomegalovirus (CMV) antibodies. Avidity of rubella, VZV, and CMV antibodies was tested by enzyme-linked immunosorbent assay modified to include a mild protein denaturant in the first wash after incubation with sera.

RESULTS

All patients had a CD3+ cell count greater than 0.500 x 10(9)/L and a CD4+ cell count greater than 0.350 x 10(9)/L). One patient had low proliferation responses to S. aureus, and one to phytohemagglutinin and pokeweed mitogen. Immunoglobulin levels, compared with those in age-related control subjects, were normal except that two patients had transient, borderline low IgG levels and two had elevated IgA levels. Specific antibody tests showed (No. of patients with positive results/No. tested) the following: diphtheria (13/13); tetanus (13/13); poliomyelitis caused by polio virus type 1 (5/9), type 2 (9/9), and type 3 (8/9); measles (11/13); rubella (11/13); and infection with VZV (5/5) and CMV (7/13). There were no significant differences in antibody avidity results between patients and control subjects for rubella (mean avidity index, 83.5 +/- 8.79 vs 85 +/- 17.6), VZV (81.6 +/- 3.98 vs 65.1 +/- 12.38), or CMV (69.3 +/- 22.31 vs 73.3 +/- 12.46).

CONCLUSIONS

Patients with "partial" DiGeorge anomalad, defined by clinical and immunologic criteria, can be immunized and for the most part can generate good antibody responses.

Generation of immunoglobulin light chain gene diversity in Raja erinacea is not associated with somatic rearrangement, an exception to a central paradigm of B cell immunity

In all vertebrate species examined to date, rearrangement and somatic modification of gene segmental elements that encode portions of the antigen-combining sites of immunoglobulins are integral components of the generation of antibody diversity. In the phylogenetically primitive cartilaginous fishes, gene segments encoding immunoglobulin heavy and light chain loci are arranged in multiple clusters, in which segmental elements are separated by only 300-400 bp. In some cases, segmental elements are joined in the germline of nonlymphoid cells (joined genes). Both genomic library screening and direct amplification of genomic DNA have been used to characterize at least 89 different type I light chain gene clusters in the skate, Raja. Analyses of predicted nucleotide sequences and predicted peptide structures are consistent with the distribution of genes into different sequence groups. Predicted amino acid sequence differences are preferentially distributed in complementarity-determining versus framework regions, and replacement-type substitutions exceed neutral substitutions. When specific germline sequences are related to the sequences of individual cDNAs, it is apparent that the joined genes are expressed and are potentially somatically mutated. No evidence was found for the presence of any type I light chain gene in Raja that is not germline joined. The type I light chain gene clusters in Raja appear to represent a novel gene system in which combinatorial and junctional diversity are absent.

Predominance of sterile immunoglobulin transcripts in a female phenotypically resembling Bruton's agammaglobulinemia

The transcription pattern of the heavy chain immunoglobulin gene locus was analyzed in a 6-month-old female with agammaglobulinemia characterized by the absence of mature B cells in peripheral blood, arrested B cell development in the bone marrow and lack of germinal center development. DNA sequencing provided no evidence of mutations within the coding region of the Bruton's tyrosine kinase gene. Polymerase chain reaction-generated cDNA libraries from blood and bone marrow were screened initially using JH and CH oligodeoxynucleotide probes and VH family-specific probes. Only 10% of the transcripts constituted mature VDJC mu recombinations. Ninety percent of the cDNA were sterile immunoglobulin transcripts comprised of: DJC mu (DH-JHC mu), JC mu (JH-C mu), EC mu (enhancer spliced to C mu), SC mu and IC mu [corresponding to switch (S) and intron (I) regions spliced to C mu]. In the mature immunoglobulin transcripts, VH use indicated germline expression with little evidence of somatic mutation. All cDNA were of the C mu type. Different D segments, D-D joining events and unknown D-like elements were noted in the DJC mu and VDJC mu transcripts. This pattern of immunoglobulin rearrangements, along with the phenotypic cell surface antigen characteristics (CD19-), suggest that an earlier arrest in B cell development than is characteristic of Bruton's X-linked agammaglobulinemia has occurred in this patient.

T-cell receptor gene homologs are present in the most primitive jawed vertebrates

The phylogenetic origins of T-cell immunity and T-cell antigen receptor (TCR) genes have not been established. A PCR approach using short, minimally degenerate oligodeoxynucleotide primers complementing conserved variable region segments amplifies TCR-like products from the genomic DNA of Heterodontus francisci (horned shark), a representative phylogenetically primitive cartilaginous fish. One of these products has been used as a probe to screen a Heterodontus spleen cDNA library and a clone was identified that is most related at the nucleotide sequence and predicted peptide levels to higher vertebrate TCR beta-chain genes. Genomic analyses of the TCR homologs indicate that recombining variable and joining region segments as well as constant region exons are encoded by extensive gene families, organized in the multicluster form, characteristic of both the immunoglobulin heavy- and light-chain gene loci in the cartilaginous fishes. Greater numbers of homologous products were identified when a probe complementing the putative constant region of the TCR homolog was used to screen the same cDNA library. A high degree of intergenic variation is associated with the putative variable region segments of these isolates. Direct evidence is presented for TCR-like genes, which presumably are associated with T-cell function, at the earliest stages in the phylogenetic emergence of jawed vertebrates.

Genomic organization and structure of Bruton agammaglobulinemia tyrosine kinase: localization of mutations associated with varied clinical presentations and course in X chromosome-linked agammaglobulinemia

X chromosome-linked agammaglobulinemia is a life-threatening disease that involves a failure in normal development of B lymphocytes and is associated with missense mutations in BTK, a gene encoding a cytoplasmic tyrosine kinase (Bruton agammaglobulinemia tyrosine kinase, EC 2.7.1.112), a member of the Tec family of protein-tyrosine kinases. The genomic organization has been determined by using conventional restriction fragment mapping, extended DNA sequencing, and PCR fragment-sizing approaches. The DNA sequences of the 18 coding exons composing BTK and their flanking-region sequences are reported; an additional exon(s) encodes a 5' untranslated segment. Single-base-pair substitutions and 4-nt deletions resulted in amino acid replacement, premature termination, frameshift, and exon deletion in a group of X chromosome-linked agammaglobulinemia patients exhibiting different clinical presentations and courses. The nature of the mutations is interpreted in terms of the genomic organization of the BTK gene and the disease course in individual patients. Several examples are found in which the same mutation occurs in unrelated patients, and one of these mutations occurs at the same codon that is substituted in the murine form of BTK, resulting in X chromosome-linked immunodeficiency disease. Considerable variation in presentation and disease course in X chromosome-linked agammaglobulinemia appears associated with the nature and position of different missense mutations.