Understanding neutropenia secondary to intrinsic or iatrogenic immune dysregulation

As a key member of the innate and adaptive immune response, neutrophils provide insights into the hematopoietic and inflammatory manifestations of inborn errors of immunity (IEI) and the consequences of immunotherapy. The facile recognition of IEI presenting with neutropenia provides an avenue for hematologists to facilitate early diagnosis and expedite biologically rationale care. Moreover, enhancing the understanding of the molecular mechanisms driving neutropenia in IEI-decreased bone marrow reserves, diminished egress from the bone marrow, and decreased survival-offers an opportunity to further dissect the pathophysiology driving neutropenia secondary to iatrogenic immune dysregulation, eg, immune checkpoint inhibitors and chimeric antigen receptor T-cell therapy.

Activation-induced deaminase is critical for the establishment of DNA methylation patterns prior to the germinal center reaction

Activation-induced deaminase (AID) initiates antibody diversification in germinal center B cells by deaminating cytosines, leading to somatic hypermutation and class-switch recombination. Loss-of-function mutations in AID lead to hyper-IgM syndrome type 2 (HIGM2), a rare human primary antibody deficiency. AID-mediated deamination has been proposed as leading to active demethylation of 5-methycytosines in the DNA, although evidence both supports and casts doubt on such a role. In this study, using whole-genome bisulfite sequencing of HIGM2 B cells, we investigated direct AID involvement in active DNA demethylation. HIGM2 naïve and memory B cells both display widespread DNA methylation alterations, of which ∼25% are attributable to active DNA demethylation. For genes that undergo active demethylation that is impaired in HIGM2 individuals, our analysis indicates that AID is not directly involved. We demonstrate that the widespread alterations in the DNA methylation and expression profiles of HIGM2 naïve B cells result from premature overstimulation of the B-cell receptor prior to the germinal center reaction. Our data support a role for AID in B cell central tolerance in preventing the expansion of autoreactive cell clones, affecting the correct establishment of DNA methylation patterns.

A novel ATM mutation associated with elevated atypical lymphocyte populations, hyper-IgM, and cutaneous granulomas

Ataxia-Telangiectasia (AT) is an immunodeficiency most often associated with T cell abnormalities. We describe a patient with a hyper-IgM phenotype and immune cell abnormalities that suggest a distinct clinical phenotype. Significant B cell abnormalities with increased unswitched memory B cells, decreased naive transitional B cells, and an elevated frequency of CD19+CD38loCD27-CD10-CD21-/low B cells expressing high levels of T-bet and Fas were demonstrated. The B cells were hyporesponsive to in vitro stimulation through the B cell receptor, Toll like receptors (TLR) 7 and 9, and CD40. T cell homeostasis was also disturbed with a significant increase in γδ T cells, circulating T follicular helper cells (Tfh), and decreased numbers of T regulatory cells. The ATM mutations in this patient are posited to have resulted in the perturbations in the frequencies and distributions of B and T cell subsets, resulting in the phenotype in this patient. KEY MESSAGES: A novel mutation creating a premature stop codon and a nonsense mutation in the ATM gene are postulated to have resulted in the unique clinical picture characterized by abnormal B and T cell populations, lymphocyte subset dysfunction, granuloma formation, and a hyper-IgM phenotype. CAPSULE SUMMARY: A patient presented with ataxia-telangiectasia, cutaneous granulomas, and a hyper-IgM phenotype; a novel combination of mutations in the ATM gene was associated with abnormal distributions, frequencies, and function of T and B lymphocyte subsets.

A tetrameric form of CD40 ligand with potent biological activities in both mouse and human primary B cells

CD40 ligand (CD40 L) expressed by activated T cells interacts with CD40 on B cells and triggers B cell survival, proliferation and differentiation. Deficiency in CD40 L or CD40 in humans causes hyper IgM syndrome due to a defect in T-B interaction that is essential for Ig gene class switch recombination (CSR). CD40 L belongs to the tumor necrosis factor family and normally forms a homotrimer on the cell surface, which is important for its biological activity. To generate a multimeric CD40 L that can be used to stimulate both mouse and human B cells, we fused the extracellular domain of mouse CD40 L, which is known to also bind human CD40, with streptavidin (SA) that forms a stable tetramer under physiological conditions. As expected, 293 T cells transiently transfected with an SA-CD40 L expression vector secreted tetrameric SA-CD40 L in the culture supernatant. The secreted SA-CD40 L exhibited > 25-fold stronger activities in inducing the survival, activation and proliferation of both mouse and human primary B cells than did an agonistic anti-mouse or anti-human CD40 antibody. In the presence of IL-4, SA-CD40 L also induced efficient CSR and plasma cell differentiation in both mouse and human B cells. Moreover, administration of SA-CD40 L in mice induced activation and proliferation of spleen B cells in vivo. These results demonstrate that the SA-CD40 L fusion protein generated in the present study recapitulates the function of membrane-bound trimeric CD40 L and has potent biological activities in both mouse and human primary B cells.

Hyper IgM Syndrome with low IgM and thrombocytosis: an unusual case of immunodeficiency

We report a 5 years old male child with low serum IgG, IgA and IgM levels, who presented with recurrent perianal and oral ulcers, intermittent fever, and protracted diarrhea. Despite the lack of typical respiratory symptoms, low serum IgM level and persistent thrombocytosis, an X-linked hyper-IgM syndrome (X-HIGM) was considered. Laboratory investigations revealed a diagnosis of hyper-IgM syndrome caused by CD40L deficiency.

Novel and recurrent AID mutations underlie prevalent autosomal recessive form of HIGM in consanguineous patients

Immunoglobulin class switch recombination deficiencies (Ig-CSR-D) are characterized by normal or elevated serum IgM level and absence of IgG, IgA, and IgE. Most reported cases are due to X-linked CD40L deficiency. Activation-induced cytidine deaminase deficiency is the most frequent autosomal recessive form, whereas CD40 deficiency is more rare. Herein, we present the first North African study on hyper IgM (HIGM) syndrome including 16 Tunisian patients. Phenotypic and genetic studies allowed us to determine their molecular basis. Three CD40LG mutations have been identified including two novels (c.348_351dup and c.782_*2del) and one already reported mutation (g.6182G>A). No mutation has been found in another patient despite the lack of CD40L expression. Interestingly, three AICDA mutations have been identified in 11 patients. Two mutations were novel (c.91T>C and c.389A>C found in one and five patients respectively), and one previously reported splicing mutation (c.156+1T>G) was found in five patients. Only one CD40-deficient patient, bearing a novel mutation (c.109T>G), has been identified. Thus, unlike previous reports, AID deficiency is the most frequent underlying molecular basis (68%) of Ig-CSR-D in Tunisian patients. This finding and the presence of specific recurrent mutations are probably due to the critical role played by inbreeding in North African populations.

[The role of immunodeficiencies in development of complications during vaccination of children with BCG vaccine]

AIM

Study of the interrelation between the presence of immune deficiency and development of complications during vaccination of newborns with BCG vaccine.

MATERIALS AND METHODS

In 24 children with complications of vaccine process in the form of cold abscess and lymphadenitis indicators of lymphocyte subpopulation levels were studied by flow cytofluorimetry on Beckman Coulter cytofluoriemter by using monoclonal antibodies with markers CD45+CD3+ - T-cell, CD45+CD3+CD4+ - T-helpers, CD45+CD3+CD8+ - T-supressors-cytotoxic killers, CD45+CD3 CD16+CD56+ - natural killers, CD45+CD3-CD19+ - B-lymphocytes. The level of IgG, IgA, IgM in sera was determined by immune diffusion method in agar by Mancini.

RESULTS

In 4 children selective deficiency of IgA, in 5 - hyper-IgM syndrome was detected, which is an innate immunodeficiency and is characterized by the lack of sera IgA, reduction of IgG level and increase of IgM. In 9 children a reduction of CD16+ natural killer lymphocytes was detected, in some cases combined with a reduction of CD8+ T-supressors-cytotoxic killers.

CONCLUSION

The reason of development of complications during BCG administration is the presence of immunodeficiency in children. In these children severe course of the vaccine process, presence of axillary lymphadenitis was observed, therapy of these children continued from 4 to 6 months.

The loss of Gnai2 and Gnai3 in B cells eliminates B lymphocyte compartments and leads to a hyper-IgM like syndrome

B lymphocytes are compartmentalized within lymphoid organs. The organization of these compartments depends upon signaling initiated by G-protein linked chemoattractant receptors. To address the importance of the G-proteins Gα_i2 and Gα_i3 in chemoattractant signaling we created mice lacking both proteins in their B lymphocytes. While bone marrow B cell development and egress is grossly intact; mucosal sites, splenic marginal zones, and lymph nodes essentially lack B cells. There is a partial block in splenic follicular B cell development and a 50-60% reduction in splenic B cells, yet normal numbers of splenic T cells. The absence of Gα_i2 and Gα_i3 in B cells profoundly disturbs the architecture of lymphoid organs with loss of B cell compartments in the spleen, thymus, lymph nodes, and gastrointestinal tract. This results in a severe disruption of B cell function and a hyper-IgM like syndrome. Beyond the pro-B cell stage, B cells are refractory to chemokine stimulation, and splenic B cells are poorly responsive to antigen receptor engagement. Gα_i2 and Gα_i3 are therefore critical for B cell chemoattractant receptor signaling and for normal B cell function. These mice provide a worst case scenario of the consequences of losing chemoattractant receptor signaling in B cells.

Ataxia-telangiectasia in a patient presenting with hyper-immunoglobulin M syndrome

Ataxia-telangiectasia (AT) and hyper-immunoglobulin M (HIGM) syndrome are both primary immunodeficiency diseases caused by different genetic defects. While a small proportion of AT patients have increased serum immunoglobulin (Ig) M concentrations during the course of a disease, a high level of IgM at onset is rare. We report the case of an 8-year-old girl who had experienced recurrent respiratory infection, cutaneous abscesses, and hepatosplenomegaly since the age of 2 years. She was diagnosed with HIGM based on the results of immunological studies, including low IgG and IgA levels and raised serum IgM concentrations. However, at the age of 4 years, a neurological examination revealed gait disturbance and telangiectatic lesions on the conjunctiva; therefore, a diagnosis of AT was suggested. In spite of regular intravenous immunoglobulin infusions and antimicrobial prophylaxis, the patient experienced several episodes of respiratory infection and eventually died of respiratory failure at the age of 8 years. Further molecular analysis revealed a novel homozygous missense mutation in exon 53 (c.8250C>T, p.2622Ala>Val) of the ATM gene. Patients with AT and the HIGM phenotype may not develop clinical characteristics of AT for some time. While patients with AT and increased serum IgM levels could have a considerably more severe disease course and a shorter survival, IgM levels could be considered a prognostic factor.

Isolated growth hormone deficiency in a patient with immunoglobulin class switch recombination deficiency

Growth hormone deficiency (GHD) may be associated with a number of immunodeficiency diseases, but its association with immunoglobulin class switch recombination (Ig CSR) deficiencies is very rare. We report the case of a patient with a history of recurrent diarrhea and respiratory infections diagnosed with hyper IgM syndrome on the basis of immunological findings (low serum levels of IgG and IgA and an elevated serum level of IgM). In view of the patient's short stature, growth hormone evaluation was performed and growth hormone deficiency confirmed. The patient received growth hormone therapy in addition to Ig replacement therapy and antibiotics and responded well. As the coding regions of the genes known to be responsible for Ig CSR (CD40L, CD40, AICDA, and UNG) were intact in our patient, this might be a new form of Ig CSR deficiency.

Congenital rubella syndrome, hyper-IgM syndrome and autoimmunity in an 18-year-old girl

Congenital rubella syndrome can be associated with disgammaglobulinaemia and autoimmune phenomena in adult and paediatric population. The aim of this article is to present the association between a congenital rubella syndrome with hypogammaglobulinaemia and hyper IgM diagnosed at the age of 8 months and autoimmune manifestations in an 18-year-old girl. A medical chart review of this patient since admission at our institution at 8 months of age was carried out. During infancy she presented the classical manifestations of a rubella syndrome (sensorineural deafness and brain calcifications in basal ganglia) with respiratory and gastrointestinal infections. She was also diagnosed of localised scleroderma and thyroiditis. She has been on intravenous immunoglobulin since diagnosis, with rapid normalisation of IgG and IgM levels, decreased incidence of infectious processes, but with persistent autoimmune phenomena. At 18 years of age she was admitted because of a thyroid mass. Fine needle aspiration biopsy was not conclusive and thyroidectomy was performed. Pathology studies showed no malignancy. She is now on replacement therapy with thyroid hormones. Our aim is to emphasise the importance of the association between autoimmune phenomena in patients with immunodeficiencies, even secondary to some infections, and the increased frequency of malignancies owing to the persistent immunologic defect in this syndrome.

Immunodeficiency and Autoimmune Phenomena in Female Hyper-IgM Syndrome

We report an unusual case that highlights the clinical problems associated with autoimmune phenomena. A female (born 1972) was referred to our hospital with systemic lupus erythematosus (SLE) diagnosis. During the follow-up (7 years), we observed the appearance and the disappearance of a lot of autoantibodies detected. The history of recurrent bacterial sinopulmonary infections since puberty and enlargement of lymphonodes, elevated IgM, very low IgA and normal IgG levels, and the variable autoantibody profile oriented toward a "defective Ig class switch recombination" disorder: the hyper-IgM syndrome. Immunodeficiency and autoimmune phenomena may occur concomitantly in the same individual and sometimes the differential diagnosis is difficult.

Regulation of aicda expression and AID activity: relevance to somatic hypermutation and class switch DNA recombination

Expression and activity of activation-induced cytidine deaminase (AID) encoded by the aicda gene are essential for immunoglobulin (Ig) gene somatic hypermutation (SHM) and class switch DNA recombination (CSR). SHM and CSR unfold, in general, in germinal centers and/are central to the maturation of effective antibody responses. AID expression is induced by activated B-cell CD40 signaling, which is critical for the germinal center reaction, and is further enhanced by other stimuli, including interleukin-4 (IL-4) secreted from CD4+ T cells or Toll-like receptor (TLR)-activating bacterial and/or viral molecules. Integration of different intracellular signal transduction pathways, as activated by these stimuli, leads to a dynamic aicda-regulating program, which involves both positively acting trans-factors, such as Pax5, HoxC4, E47, and Irf8, and negative modulators, such as Blimp1 and Id2, to restrict aicda expression primarily to germinal center B cells. The phosphatidylinositol 3-kinase (PI 3-K), which functions downstream of activated B-cell receptor (BCR) signaling, likely plays an important role in triggering the downregulation of aicda expression in postgerminal center B cells and throughout plasmacytoid differentiation. In B cells undergoing SHM and CSR, AID activity, and, possibly, AID targeting to the Ig locus are regulated at a posttranslational level, including AID dimerization/oligomerization, nuclear/cytoplasmic AID translocation, and phosphorylation of the AID Ser38 residue by protein kinase A (PKA). Here, we discuss the role of B-cell activation signals, transcription regulation programs, and posttranslational modifications in controlling aicda expression and AID activity, thereby delineating an integrated model of modulation of SHM and CSR in the germinal center reaction.