B-cell extrinsic CR1/CR2 promotes natural antibody production and tolerance induction of anti-αGAL–producing B-1 cells

Abstract

B-1b cells produce IgM natural antibodies against ␣1-3Gal␤1-4GlcNAc (␣Gal). These can be tolerized by nonmyeloablative induction of mixed chimerism using ␣Gal-positive (␣Gal؉) donor marrow. We assessed the role of CR1/2 in this model for induction of tolerance of B-1b cells. Mixed hematopoietic chimerism was induced in ␣1-3galactosyltransferase (GalT ؊/؊ ) and GalT ؊/؊ Cr2 ؊/؊ mice with ␣Gal؉ BALB/c marrow donors. Anti-␣Gal Ab and anti␣Gal Ab-producing B cells became undetectable in GalT ؊/؊ chimeras, whereas they persisted in chimeric GalT ؊/؊ Cr2 ؊/؊ mice. To determine whether CR1/2 expression on stromal cells and/or hematopoietic cells was critical for B-1-cell tolerance, we generated GalT ؊/؊ radiation chimeras in which CR1/CR2 was expressed on either stromal cells, hematopoietic cells, neither, or both. After induction of mixed chimerism from ␣Gal؉ IntroductionHumans and old-world primates lack functional ␣1-3galactosyltrans-ferase (GalT) and produce natural antibodies (NAbs) that recognize Gal␣1-3Gal␤1-4GlcNAc (␣Gal). Pigs express high levels of ␣Gal antigen on their cell surfaces, and hyperacute rejection is induced by anti-␣Gal NAb in pig-to-primate xenotransplantation. 1 GalT Ϫ/Ϫ mice lack the ability to produce ␣Gal and, like humans, produce anti-␣Gal NAb. These mutant mice thereby provide a model for the investigation of anti-␣Gal B-cell responses and tolerance. 2,3 Using myeloablative and nonmyeloablative conditioning regimens, we have previously shown that NAb-producing B cells in GalT Ϫ/Ϫ mice can be tolerized via mixed chimerism induction. [4][5][6] Both pre-existing and newly developing B cells producing anti␣Gal Ab are tolerized by the achievement of chimerism from ␣Gal-positive (␣Galϩ) donors. Using nonmyeloablative bone marrow transplantation (BMT), permanent acceptance of ␣Galϩ heart allografts and xenografts was achieved in GalT Ϫ/Ϫ mice. 7 We have observed that B-1b cells bearing anti-␣Gal receptors in the peritoneal cavity (PerC), which are IgM high CD5 Ϫ CD43 ϩ Mac1 ϩ and lack CD21 (CR2) expression, are the main progenitors of anti-␣Gal Ab-producing cells. These PerC cells lose Mac1 expression in association with migration into the spleen and transition to Ab-secreting cells. 8,9 Complement receptor 1 (CR1, CD35), the receptor for C3b and C4b, and CR2 (CD21), the receptor for iC3b and C3d, g, are coexpressed on B cells and follicular dendritic cells (FDCs) in both humans and mice. [10][11][12] CD21 is a splice variant of CD35, and Cr2 Ϫ/Ϫ mice therefore lack both CD21 and CD35. Coupled with CR1 or CD19, CR2 regulates B-cell activation and differentiation and promotes memory generation and immunoglobulin class switching. 13 CR1/CR2 on marginal zone B cells also contributes an initial step toward adaptive immunity by transporting immune complexes onto FDCs. 14-17 Impaired B-cell responses to T-dependent and T-independent antigens have been observed using Cr2 Ϫ/Ϫ mice. 13,[17][18][19][20][21][22] Complement and complement receptors have also been implicated in self-tolerance of B cells in a...

TLR9 in Peritoneal B-1b Cells Is Essential for Production of Protective Self-Reactive IgM To Control Th17 Cells and Severe Autoimmunity

“…mice. However, MyD88 signaling is not only involved in the TLR9-dependent development of anti-nucleosome IgG2c and IgG2b autoantibodies but also in cell maturation via other TLRs (e.g., TLR7) (7-12, 14, 15, 17, 40, 41 analyzed by CD5 expression at day 7. that B-1b cells have a tolerogenic function, but underlying mechanisms have been unknown (44,45 Taken together, our data suggest that the tolerogenic function of MyD88-dependent TLR9 signaling is mediated by the production of self-reactive serum IgM Abs by peritoneal B-1b cells, which protects from uncontrolled accumulation of Th17 cells and severe autoimmunity. These findings provide new insight in the tolerogenic function of TLR9, B-1b cells, and self-reactive IgM to control autoimmunity and have implications for the development of TLR ligand-dependent therapies and B cell depletion protocols as a treatment for autoimmunity.…”

Rapidly induced, T-cell–independent xenoantibody production is mediated by marginal zone B cells and requires help from NK cells

“…On a FACSVantage (Becton Dickinson, San Jose, CA), CD21 neg CD23 neg B1b and CD21 high CD23 low MZB cells were sorted, 15,19 collected, and resuspended in PBS for intravenous injection. Purity of selected cell populations was more than 90%.…”

“…Accordingly, xenografts transplanted on day 2 or 14 were accepted indefinitely (Table 1; groups F,G) without IgM xenoantibody production (not shown). In contrast, xenografting at week 4 after TBI, when MZB cells had recovered, again resulted in acute vascular rejection (Table 1; group H) accompanied with high IgM xenoantibody levels (not shown).In order to confirm that MZB cells and not B1b lymphocytes were responsible for rapidly induced IgM xenoantibody production, MACS-enriched CD19 ϩ B cells from BALB/c nude spleens were purified using fluorescence-activated cell sorter (FACS) sorting into CD21 high CD23 low MZB cells and CD21 neg CD23 neg B1b cells 15,19 (Figure 3A). CB17 severe combined immunodeficiency (SCID) mice were given 2 to 5 ϫ 10 6 subset B cells intravenously on day 0, and 200 L whole hamster blood on day 7.…”

Immunological Challenges and Therapies in Xenotransplantation

“…The resulting activation of helper T lymphocytes enables the B cells to complete their activation process, ultimately resulting in proliferation, isotype switching, and the generation of plasma cells and high-affinity anti-aGal antibodies (Tanemura et al 2000). Finally, there are reports of follicular dendritic cells expressing complement receptors 1 and 2 being involved in the presentation of immune complexes to aGal-reactive B cells and being needed for antigen-specific antiaGal response (Shimizu et al 2007). At this stage, thanks to the many approaches pursued with a view to removing preexisting anti-aGal antibodies and controlling their effector functions, HAR of a solid organ xenograft has become a rare event.…”