Definition of a Novel Cellular Constituent of the Bone Marrow That Regulates the Response of Immature B Cells to B Cell Antigen Receptor Engagement

120

101

NK cells are innate immune lymphocytes and play a key role in both innate and adaptive immunity. Their pivotal functions in vivo have been illustrated in mice by means of their ablation with NK cell-depleting Abs, particularly anti-asialo GM1 (ASGM1). In this study, we show that the whole population of basophils constitutively expresses ASGM1 as well as CD49b (DX5) as does the NK cell population and was ablated in vivo by anti-ASGM1 as efficiently as by a basophil-depleting anti-FcεRIα Ab. Anti-ASGM1–mediated basophil depletion was operative as for NK cell depletion in various mouse strains, irrespective of NK1 allotype and MHC H2 haplotype, including C57BL/6, BALB/c, C3H, and A/J mice. These results identified basophils as a previously unrecognized target of anti-ASGM1–mediated cell depletion and raised concern about possible contribution of basophils, rather than or in addition to NK cells, to some of phenotypes observed in anti-ASGM1–treated mice. Indeed, regardless of the presence or absence of NK cells in mice, anti-ASGM1 treatment abolished the development of IgE-mediated chronic cutaneous allergic inflammation as efficiently as did the treatment with basophil-depleting Ab. Given the fact that basophils have recently been shown to play crucial roles in a variety of immune responses, our finding of the off-target effect on basophils issues a grave warning about the use of anti-ASGM1 and underscores the need for careful interpretation of phenotypes observed in anti-ASGM1–treated mice.

Section: Discussionmentioning

confidence: 99%

NK Cell-Depleting Anti-Asialo GM1 Antibody Exhibits a Lethal Off-Target Effect on Basophils In Vivo

Nishikado

Mukai

Kawano

et al. 2011

120

101

“…Anti-Ig␤ stimulation of sIgM high transitional splenic B cells from 6-1/V 1A mice was found to result in slight to moderate up-regulation of RAG expression but not L chain rearrangement as scored by dsDNA breaks at J coding elements (59). However, when BCRinduced apoptosis of cultured sIgM high transitional splenic B cells is inhibited by coculture with Thy1 dull DX5 ϩ cells from normal BM, up-regulated expression of both RAG and dsDNA breaks at J coding elements is observed (76,77). These results suggest that BCR-stimulated sIgM high transitional splenic B cells may undergo apoptosis or receptor editing, depending on the microenvironment in which these cells encounter Ag (76,77).…”

Section: Rag Expression and L Chain Editing In B Cells Deficient For mentioning

confidence: 98%

“…However, when BCRinduced apoptosis of cultured sIgM high transitional splenic B cells is inhibited by coculture with Thy1 dull DX5 ϩ cells from normal BM, up-regulated expression of both RAG and dsDNA breaks at J coding elements is observed (76,77). These results suggest that BCR-stimulated sIgM high transitional splenic B cells may undergo apoptosis or receptor editing, depending on the microenvironment in which these cells encounter Ag (76,77). Our findings with 56RV 8 and nontransgenic C57BL/6 mice extend the studies cited above and show that sIgM low T3 transitional SPL B cells contain dsDNA breaks indicative of ongoing L chain rearrangement.…”

Section: Rag Expression and L Chain Editing In B Cells Deficient For mentioning

confidence: 99%

Antigen Receptor Editing in Anti-DNA Transitional B Cells Deficient for Surface IgM

Kiefer

Nakajima

Oshinsky

et al. 2008

In response to encounter with self-Ag, autoreactive B cells may undergo secondary L chain gene rearrangement (receptor editing) and change the specificity of their Ag receptor. Knowing at what differentiative stage(s) developing B cells undergo receptor editing is important for understanding how self-reactive B cells are regulated. In this study, in mice with Ig transgenes coding for anti-self (DNA) Ab, we report dsDNA breaks indicative of ongoing secondary L chain rearrangement not only in bone marrow cells with a pre-B/B cell phenotype but also in immature/transitional splenic B cells with little or no surface IgM (sIgM−/low). L chain-edited transgenic B cells were detectable in spleen but not bone marrow and were still found to produce Ab specific for DNA (and apoptotic cells), albeit with lower affinity for DNA than the unedited transgenic Ab. We conclude that L chain editing in anti-DNA-transgenic B cells is not only ongoing in bone marrow but also in spleen. Indeed, transfer of sIgM−/low anti-DNA splenic B cells into SCID mice resulted in the appearance of a L chain editor (Vλx) in the serum of engrafted recipients. Finally, we also report evidence for ongoing L chain editing in sIgMlow transitional splenic B cells of wild-type mice.

“…Although the mechanism by which myeloid DCs were increased during the progression of leukemia is unclear, the ability of NK cells to kill immature DCs (26,27) suggests that an increase in the number of immature NK cells with low killing activity may lead to the overproduction of DCs in this model. DX5 ϩ cells are a heterogeneous population, and subsets of CD8 ϩ T cells (28) and immature B cells (29) have been reported to express DX5. To confirm that our DX5 ϩ cells are actually NK cells, we assayed their surface markers.…”

Section: Discussionmentioning

confidence: 99%

Immature NK Cells Suppress Dendritic Cell Functions during the Development of Leukemia in a Mouse Model

Ebata¹,

Shimizu²,

Nakayama³

et al. 2006

To analyze the mechanisms by which cancer cells escape from hosts’ immune surveillance, we investigated the changes in immune status during the progression of leukemia induced by injecting mice with WEHI-3B cells. In the bone marrow (BM) of leukemic mice, only DX5+CD3− cells were continuously increased, despite the progression of leukemia. In addition, DX5+CD3− cells were rapidly increased in peripheral blood (PB) 20 days after inoculation. We also found that myeloid dendritic cells (DCs) expressing low levels of I-Ad and having low allo-T cell stimulatory activity were markedly increased in PB and spleen. The increase in DX5+ cells in BM was thought to be induced by soluble factors from leukemic cells. DX5+ cells from leukemic mice were CD3−, B220−, Gr-1−, CD14−, CD94−, Ly-49C/F−, asialo GM1+, CD25+, CD122+, Thy-1bright, and c-kitdim and showed low killing activity against YAC-1 cells, suggesting that those DX5+ cells were immature NK cells. NK cells from leukemic PB down-regulated the expression of I-Ad on DCs, an effect mediated by TGF-β. Moreover, these NK cells significantly suppressed the allo-T cell stimulatory activity of DCs, an effect requiring cell-to-cell contact between NK cells and DCs and thought to involve CD25. Importantly, NK cells from leukemic PB inhibited generation of autotumor-specific CTL induced by DCs in primary MLR or by DC immunization. In conclusion, we identified circulating immature NK cells with immunosuppressive activities. These cells may be important for understanding the involvement of the host immune system during the development of leukemia.