Follicular dendritic cells mediated maintenance of primary lymphocyte cultures for long-term analysis of a functional in vitro immune system

Follicular dendritic cells (FDCs) periodically arrange membrane-bound immune complexes (ICs) of T-dependent Ags 200–500Å apart, and in addition to Ag, they provide B cells with costimulatory signals. This prompted the hypothesis that Ag in FDC-ICs can simultaneously cross-link multiple BCRs and induce T cell-independent (TI) B cell activation. TI responses are characterized by rapid IgM production. OVA-IC-bearing FDCs induced OVA-specific IgM in anti-Thy-1-pretreated nude mice and by purified murine and human B cells in vitro within just 48 h. Moreover, nude mice immunized with OVA-ICs exhibited well-developed GL-7+ germinal centers with IC-retaining FDC-reticula and Blimp-1+ plasmablasts within 48 h. In contrast, FDCs with unbound-OVA, which would have free access to BCRs, induced no germinal centers, plasmablasts, or IgM. Engagement of BCRs with rat-anti-mouse IgD (clone 11–26) does not activate B cells even when cross-linked. However, B cells were activated when anti-IgD-ICs, formed with Fc-specific rabbit anti-rat IgG, were loaded on FDCs. B cell activation was indicated by high phosphotyrosine levels in caps and patches, expression of GL-7 and Blimp-1, and B cell proliferation within 48 h after stimulation with IC-bearing FDCs. Moreover, anti-IgD-IC-loaded FDCs induced strong polyclonal IgM responses within 48 h. Blockade of FDC-FcγRIIB inhibited the ability of FDC-ICs to induce T-independent IgM responses. Similarly, neutralizing FDC-C4BP or -BAFF, to minimize these FDC-costimulatory signals, also inhibited this FDC-dependent IgM response. This is the first report of FDC-dependent but TI responses to T cell-dependent Ags.

Section: Discussionmentioning

confidence: 99%

T-Independent Antibody Responses to T-Dependent Antigens: A Novel Follicular Dendritic Cell-Dependent Activity

Shikh

Sayed²,

Szakal³

et al. 2009

“…In the absence of FDC, most B cells died, and although they produced Abs between days 0 and 7, very little Ab production was obtained between days 7-14. FDC are known to protect B cells from apoptotic death (10,44), and the B cells surviving and producing Ab in the day 7-14 period have interacted with the FDC and associated CD23. Addition of Tg FDC resulted in a decrease of IgE from 2030 to 470 ng/ml (p Ͻ 0.03), whereas no difference in IgG production was obtained when Tg and LM-FDC were compared.…”

Section: Discussionmentioning

confidence: 99%

Suppression of IgE Responses in CD23-Transgenic Animals Is Due to Expression of CD23 on Nonlymphoid Cells

Payet-Jamroz

Helm

et al. 2001

Self Cite

Serum IgE is suppressed in CD23-transgenic (Tg) mice where B cells and some T cells express high levels of CD23, suggesting that CD23 on B and T cells may cause this suppression. However, when Tg B lymphocytes were compared with controls in B cell proliferation and IgE synthesis assays, the two were indistinguishable. Similarly, studies of lymphokine production suggested that T cell function in the Tg animals was normal. However, adoptive transfer studies indicated that suppression was seen when normal lymphocytes were used to reconstitute Tg mice, whereas reconstitution of controls with Tg lymphocytes resulted in normal IgE responses, suggesting that critical CD23-bearing cells are irradiation-resistant, nonlymphoid cells. Follicular dendritic cells (FDC) are irradiation resistant, express surface CD23, and deliver iccosomal Ag to B cells, prompting us to reason that Tg FDC may be a critical cell. High levels of transgene expression were observed in germinal centers rich in FDC and B cells, and IgE production was inhibited when Tg FDCs were cultured with normal B cells. In short, suppressed IgE production in CD23-Tg mice appears to be associated with a population of radioresistant nonlymphoid cells. FDCs that interface with B cells in the germinal center are a candidate for explaining this CD23-mediated IgE suppression.

“…FDCs function in capture and long-term retention of immune complexes (ICs) (5-7), the blocking of apoptosis, the survival of specific B cells (8,9), and the promotion of the development of potent high-affinity (10) recall responses (11,12). The capture and retention of ICs are mediated by an array of cell surface receptors that include Fc␥RII (13,14) and complement receptors (complement receptors 1 and 2 (CR1/ 2)) (15)(16)(17).…”

Section: T He Follicular Dendritic Cells (Fdcs)mentioning

confidence: 99%

“…Numerous studies indicate the importance of Fc␥RII and CR1/2 in IC trapping and mediation of costimulatory signals to B cells in humans as well as mice (3,7,9,11,13). However, potential age-related changes in the function and molecular interactions of the Fc␥RII and CR1/2 have not been determined.…”

Section: T He Follicular Dendritic Cells (Fdcs)mentioning

confidence: 99%

Altered Regulation of FcγRII on Aged Follicular Dendritic Cells Correlates with Immunoreceptor Tyrosine-Based Inhibition Motif Signaling in B Cells and Reduced Germinal Center Formation

Aydar¹,

Balogh²,

Tew

et al. 2003

Aging is associated with reduced trapping of Ag in the form of in immune complexes (ICs) by follicular dendritic cells (FDCs). We postulated that this defect was due to altered regulation of IC trapping receptors. The level of FDC-M1, complement receptors 1 and 2, FcγRII, and FDC-M2 on FDCs was immunohistochemically quantitated in draining lymph nodes of actively immunized mice for 10 days after Ag challenge. Initially, FDC FcγRII levels were similar but by day 3 a drastic reduction in FDC-FcγRII expression was apparent in old mice. FDC-M2 labeling, reflecting IC trapping, was also reduced and correlated with a dramatic reduction in germinal center (GC) B cells as indicated by reduced GC size and number. Nevertheless, labeling of FDC reticula with FDC-M1 and anti-complement receptors 1 and 2 was preserved, indicating that FDCs were present. FDCs in active GCs normally express high levels of FcRs that are thought to bind Fc portions of Abs in ICs and minimize their binding to FcRs on B cells. Thus, cross-linking of B cell receptor and FcR via IC is minimized, thereby reducing signaling via the immunoreceptor tyrosine-based inhibition motif. Old FDCs taken at day 3, when they lack FcγRII, were incapable of preventing immunoreceptor tyrosine-based inhibition motif signaling in wild-type B cells but old FDCs stimulated B cells from FcγRIIB−/− mice to produce near normal levels of specific Ab. The present data support the concept that FcR are regulated abnormally on old FDCs. This abnormality correlates with a reduced IC retention and with a reduced capacity of FDCs to present ICs in a way that will activate GC B cells.