Long-term immunosuppressive treatment of a child with Takayasu's arteritis and high IgE immunoglobulins

Transcriptional Analysis of the Human IgE-Expressing Plasma Cell Differentiation Pathway

IgE is secreted by plasma cells (PCs) and is central to allergic disease. Using an ex vivo tonsil B cell culture system, which mimics the Th2 responses in vivo, we have recently characterized the development pathway of human IgE-expressing PCs. In this system, as in mice, we reported the predisposition of IgE-expressing B cells to differentiate into PCs. To gain a comprehensive understanding of the molecular events involved in the differentiation of human IgE⁺ B cells into PCs we have used the Illumina HumanHT-12 v4 Expression BeadChip array to analyse the gene expression profile of ex vivo generated human IgE⁺ B cells at various stages of their differentiation into PCs. We also compared the transcription profiles of IgE⁺ and IgG1⁺ cells to discover isotype-specific patterns. Comparisons of IgE⁺ and IgG1⁺ cell transcriptional profiles revealed molecular signatures specific for IgE⁺ cells, which diverge from their IgG1⁺ cell counterparts upon differentiation into PCs. At the germinal center (GC) stage of development, unlike in some mouse studies of IgE biology, we observed similar rates of apoptosis and no significant differences in the expression of apoptosis-associated genes between the IgE⁺ and IgG1⁺ B cells. We identified a gene interaction network associated with early growth response 1 (EGR1) that, together with the up-regulated IRF4, may account for the predisposition of IgE⁺ B cells to differentiate into PCs. However, despite their swifter rates of PC differentiation, the transcription profile of IgE⁺ PCs is more closely related to IgE⁺ and IgG1⁺ plasmablasts (PBs) than to IgG1⁺ PCs, suggesting that the terminal differentiation of IgE⁺ cells is impeded. We also show that IgE⁺ PCs have increased levels of apoptosis suggesting that the IgE⁺ PCs generated in our in vitro tonsil B cell cultures, as in mice, are short-lived. We identified gene regulatory networks as well as cell cycle and apoptosis signatures that may explain the diverging PC differentiation programme of these cells. Overall, our study provides a detailed analysis of the transcriptional pathways underlying the differentiation of human IgE-expressing B cells and points to molecular signatures that regulate IgE⁺ PC differentiation and function.

Allergy for a lifetime?

As the key molecule of type-I-hypersensitivity, IgE provides specificity for the allergen and links it to the allergic effector functions. Antibodies are secreted by plasma cells and their precursors, the plasma blasts. The fate of plasma cells is a subject of controversy, with respect to their lifetime and persistence in the absence of allergen. In general, plasma cells were for a long time considered as short-lived end products of B-cell differentiation, and many of them are short-lived, although already for more than 20 years evidence has been provided that IgE-secreting plasma cells can persist over months. Today long-lived, "memory" plasma cells are considered to represent a distinct cellular entity of immunological memory, with considerable therapeutic relevance. Long-lived plasma cells resist current therapeutic and experimental approaches such as immunosuppression, e.g. cyclophosphamide, steroids, X-ray irradiation, anti-CD20 antibodies and anti-inflammatory drugs, while the chronic generation of short-lived plasma cells is sensitive to conventional immunosuppression. The seasonal variation in pollen-specific IgE can be suppressed by immunotherapy, indicating that component of the IgE response, which is stimulated with pollen allergen is susceptible to suppression. Targeting of the remaining long-lived, allergen-specific plasma cells, providing the stable IgE-titers, represents a therapeutic challenge. Here we discuss recent evidence suggesting, why current protocols for the treatment of IgE-mediated allergies fail: Memory plasma cells generated by inhalation of the allergen become long-lived and are maintained preferentially in the bone marrow. They do not proliferate, and are refractory to conventional therapies. Current concepts target plasma cells for depletion, e.g. the proteasome inhibitor bortezomib, BAFF and APRIL antagonists and autologous hematopoietic stem cell transplantation.

Induction of long-lived allergen-specific plasma cells by mucosal allergen challenge

BACKGROUND

Allergen-specific IgE antibodies are responsible for the pathogenesis of type I hypersensitivity. In patients with allergy, IgE titers can persist in the apparent absence of allergen for years. Seasonal allergen exposure triggers clinical symptoms and enhances allergen-specific IgE. Whether allergen-specific plasma cells originating from seasonal allergen exposures can survive and become long-lived is so far unclear.

OBJECTIVE

We analyzed the localization and lifetimes of allergen-specific IgE-secreting, IgA-secreting, and IgG(1)-secreting plasma cells after allergen inhalation in an ovalbumin-induced murine model of allergic asthma.

METHODS

Ovalbumin-specific IgG(1)-secreting, IgA-secreting, and IgE-secreting cells in lungs, spleen, and bone marrow were isolated and tested for antibody secretion by the ELISpot technique. Longevity of ovalbumin-specific plasma cells was determined by cyclophosphamide treatment, which depletes proliferating plasmablasts but leaves plasma cells untouched. Ovalbumin aerosol-induced infiltrates in lungs were localized by confocal microscopy.

RESULTS

Long-lived ovalbumin-specific plasma cells were generated by systemic sensitization and survived in bone marrow and spleen, maintaining systemic ovalbumin-specific titers of IgG, IgA, and IgE. On inhalation of ovalbumin-containing aerosol, sensitized mice developed airway inflammation and more ovalbumin-specific IgG(1)-secreting, IgA-secreting, and IgE-secreting cells in the lungs and in secondary lymphoid organs. These plasma cells joined the pool of ovalbumin-specific plasma cells in the bone marrow and became long-lived-that is, they are resistant to cyclophosphamide. Termination of ovalbumin inhalation depleted ovalbumin-specific plasma cells from the lungs, but they persisted in spleen and bone marrow.

CONCLUSION

Our results show that inhalation of aerosolized allergen generates long-lived, allergen-specific IgG(1)-secreting, IgA-secreting, and IgE-secreting plasma cells that survive cytostatic treatment.

Takayasu arteritis in children

Takayasu arteritis (TA) is a large vessel vasculitis that usually affects young female patients during the second and third decades of life, but has been reported in children as young as 24 months of age. Aim of this report was to describe four children (two girls) with TA, as well as summarizing main published studies. The mean age at presentation of our cases was 11 years (range 8-15). Three patients were Caucasians and one Asian. Arterial hypertension was the commonest mode of presentation followed by systemic symptoms. Other related symptoms were due to ischemia and consisted of abdomen, chest, and limb pain. An abdominal bruit was noted in only one patient. Inflammation markers were always abnormal. Angiography was performed in all cases; left subclavian artery and common carotid artery were more frequently involved. Renal artery stenosis was observed in two patients. One boy was diagnosed as having an associated immune deficiency (Wiskott-Aldrich syndrome). Treatment modalities included prednisone (n = 4), methotrexate (n = 3), and mycophenolate mofetil (MMF) (n = 1). Surgery was required in two patients. Follow-up ranged from 3 to 10 years since diagnosis. In three cases antihypertensive drugs and methotrexate were stopped, and prednisone was reduced to 7.5 mg/day.

Competence and competition: the challenge of becoming a long-lived plasma cell

Plasma cells provide humoral immunity. They have traditionally been viewed mainly as short-lived end-stage products of B-cell differentiation that deserve little interest. This view is changing, however, because we now know that plasma cells can survive for long periods in the appropriate survival niches and that they are an independent cellular component of immunological memory. Studies of the biology of plasma cells reveal a mechanism of intriguing simplicity and elegance that focuses memory provided by plasma cells on recently encountered pathogens while minimizing the 'fading' of memory for pathogens encountered in the distant past. This mechanism is based on competition for survival niches between newly generated plasmablasts and older plasma cells.