The rat mAbs R52.120 and R52.625 inhibit the action of IL-5 on both IL-5-sensitive cell lines and freshly isolated splenic B lymphocytes. Neither antibody inhibits the proliferative cell responses promoted by IL-2, IL-3, or IL-4. Purified R52.120+ lymphoid spleen cells contain 15-20-fold higher numbers of B lymphocytes responding to IL-5 in the form of maturation into antibody-producing cells. By immunofluorescence staining and flow fluorocytometry, the R52.120 and R52.625 antibodies bound to all 12 IL-5-sensitive cell lines tested. Both antibodies react with 2-4% cells in the spleen, 5% lymphoid cells, and 10-15% myeloid cells in the bone marrow, and 10-14% in the peritoneum of C57BL/6, DBA/2, and BALB/c adult mice. No positive cells for either antibody were detected in the thymus and lymph nodes of these mice. Both R52.120 and R52.625 antibodies specifically inhibit the binding of radiolabeled IL-5 to its receptor. Finally, R52.120 and R52.625 antibodies precipitate from 35S-methionine-labeled IL-5-R+ cell lysates three proteins with Mr 46,000, 130,000, and 140,000. Taken together from these results, we conclude that the R52.120 and R52.625 mAbs recognize epitopes on the IL-5-R complex very close or identical to the IL-5 binding sites.

10.1084/jem.169.5.1693

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THE FUSION GENE PAX5/TEL AS A MODEL FOR FUNCTIONAL ALTERATIONS OF THE PAX5 GENE IN PEDIATRIC LAL; IDENTIFICATION OF NEW INJURIES IN AIEOP PATIENTS

G. Fazio Cazzaniga Chiara Palmi Luciana Impera Marta Galbiati

PAX5

Identification

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In vivo evidence for an instructive role of fms-like tyrosine kinase-3 (FLT3) ligand in hematopoietic development

Haematologica (2014)

Panagiotis Tsapogas Lee Kim Swee Anja Nusser Natko Nuber Matthias Kreuzaler

Cytokines are essential regulators of hematopoiesis, acting in an instructive or permissive way. Fms-like tyrosine kinase 3 ligand (FLT3L) is an important cytokine for the development of several hematopoietic populations. Its receptor (FLT3) is expressed on both myeloid and lymphoid progenitors and deletion of either the receptor or its ligand leads to defective developmental potential of hematopoietic progenitors. In vivo administration of FLT3L promotes expansion of progenitors with combined myeloid and lymphoid potential. To investigate further the role of this cytokine in hematopoietic development, we generated transgenic mice expressing high levels of human FLT3L. These transgenic mice displayed a dramatic expansion of dendritic and myeloid cells, leading to splenomegaly and blood leukocytosis. Bone marrow myeloid and lymphoid progenitors were significantly increased in numbers but retained their developmental potential. Furthermore, the transgenic mice developed anemia together with a reduction in platelet numbers. FLT3L was shown to rapidly reduce the earliest erythroid progenitors when injected into wild-type mice, indicating a direct negative role of the cytokine on erythropoiesis. We conclude that FLT3L acts on multipotent progenitors in an instructive way, inducing their development into myeloid/lymphoid lineages while suppressing their megakaryocyte/erythrocyte potential.

Lymphopoiesis

Megakaryocytopoiesis

10.3324/haematol.2013.089482

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FRI0476 Reconstitution of the Peripheral B Lymphocyte Compartment in Patients with Anca-Associated Vasculitides Treated with Rituximab for Relapsing or Refractory Disease

Annals of the Rheumatic Diseases (2014)

Nils Venhoff Lena Nießen Matthias Kreuzaler A Rolink Marta Rizzi

Background

The dynamics of B cell reconstitution in relapsing or refractory ANCA-associated vasculitides (AAV) treated with rituximab (RTX) followed by standard immunosuppressants are not clear. While in patients with rheumatoid arthritis B cell repopulation generally starts 6 to 9 months after RTX therapy, an impaired early B-lymphocyte development resulting in a protracted peripheral B cell repopulation was reported recently in some AAV patients after B cell depletion with RTX.

Objectives

This is of clinical importance as the relapse rates in AAV after discontinuation of RTX therapy are high, and there are no data on safety and efficacy of RTX retreatment in persistently B cell depleted patients. Furthermore, there are no defined parameters that could guide RTX retreatment. To date the frequency of AAV patients with impaired peripheral B cell regeneration and the mechanism leading to the constricted regenerative capacity of the B cell compartment are unknown.

Methods

We analysed in a single center cohort comprising 125 patients with granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) the B cell repopulation kinetics in 37 patients treated for relapsing or refractory disease with RTX followed by maintenance immunosuppressants in most patients. Furthermore, we report on serum concentrations of the B cell-activating factor of the TNF family (BAFF, BLyS) and immunoglobulin concentrations as well as on peripheral B cell subpopulations in a subgroup of patients that relapsed after RTX treatment.

Results

B cells were re-detectable in only one patient within the 9 months period after RTX treatment. After a mean observation time of 21 months 14 patients (41%) had started repopulating the peripheral B cell compartment, with 7 of the 14 patients having re-detectable B cells within the first year after RTX treatment. In 20 patients (59%) no repopulation occurred within the observation period. Eight of these patients were observed for more than 24 months without a starting B cell repopulation. BAFF concentrations in serum of AAV patients after RTX treatment were increased compared to healthy controls and correlated inversely with peripheral B cell numbers, IgG- and IgA concentrations. Serum immunoglobulin concentrations declined significantly after RTX treatment, and serum IgG concentrations correlated with peripheral B cell numbers after RTX therapy. 13 patients relapsed after RTX treatment. All of the 13 relapses either occurred after beginning B cell reconstitution or were accompanied by rising ANCA titres. In patients that relapsed after RTX the B lymphocyte compartment consisted mainly of switched memory B cells.

Conclusions

In summary, in our cohort of GPA and MPA patients treated with RTX followed by a standard maintenance immunosuppressive therapy a high proportion of patients had a long-lasting B cell depletion. Retreatment with RTX in long-term B cell depleted patients warrants close monitoring for adverse events and especially infectious complications and monitoring of serum immunoglobulin. Relapses after RTX treatment either occurred after beginning B cell reconstitution or were accompanied by rising ANCA titres.

Disclosure of Interest

None declared

DOI

10.1136/annrheumdis-2014-eular.4213

Refractory (planetary science)

10.1136/annrheumdis-2014-eular.4213

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Repopulation of SCID mice with long-term in vitro proliferating pre-B-cell lines from normal and autoimmune disease-prone mice

Research in Immunology (1994)

A Rolink Luc Reininger Yoshihiro Oka Christian P. Kalberer Thomas Winkler

Repopulation

10.1016/s0923-2494(94)80199-1

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Citations (9)