Augmentation of in vitro humoral immune responses in the mouse by an antibody to IgD

Development and pharmacological validation of novel methods of B cell activation in rat whole blood

INTRODUCTION

Whole blood functional assays are pharmacologically relevant in the drug discovery process to evaluate potency in a relevant biological matrix, to support establishment of PK/PD relationships and to aid in human dose predictions. However development of B cell activation assays by BCR ligation in rat whole blood has not been previously described. The aim of the present study was to develop novel methods of B cell activation in rat whole blood.

METHODS

B cell activation in rat whole blood was evaluated by measuring CD86 up-regulation via flow cytometry. Rat B cells in whole blood were stimulated with dextran-coupled anti-IgD or a combination of anti-IgD and TLR9 agonist. BTK, SYK, and PI3Kδ inhibitors were added to rat whole blood prior to activation with dextran-coupled anti-IgD or anti-IgD and TLR9 agonist combination for pharmacological validation of the assay.

RESULTS

Both methods of stimulation in rat whole blood evoked robust B cell activation in a uni-modal fashion. Highly selective inhibitors of BTK, SYK, and PI3Kδ dose-dependently attenuated B cell activity evoked by both dextran-coupled anti-IgD and combined anti-IgD and TLR9 agonist. Compound potencies and rank order determined by the two assays were comparable.

DISCUSSION

Two novel methods were developed to stimulate B cells in rat whole blood, that have the potential to be used to support drug discovery efforts in the therapeutic targeting of B cells. Furthermore, we pharmacologically validated these whole blood assays using highly selective inhibitors of BTK, SYK, and PI3Kδ, signaling kinases which are downstream of the B cell receptor.

Heterogeneity of M-cell-associated B and T cells in human Peyer's patches

The specialized M cells in the follicle-associated epithelium (FAE) of Peyer's patches (PP) represent an intimate interphase between luminal antigens and gut-associated lymphoid tissue (GALT). M cells form pockets that contain clusters of leucocytes probably involved in the first encounter with antigens from the gut lumen. Three-colour immunofluorescence in situ phenotyping of these leucocytes in humans revealed about equal numbers of B (CD19/20+) and T(CD3+) lymphocytes, the latter mainly CD4+ (median 73%, range 40-90%), but relatively few macrophages (CD68+). Most B cells (90%) were positive for surface IgM (sIgM) and often co-expressed sIgD (median 34%, range 6-60%). Occasional B cells (median 2%) did not express CD45RA (range 0-15%) and 13% virtually lacked HLA-DR (range 0-40%). Some B and T lymphocytes expressed the nuclear proliferation marker Ki-67 (range 1-10%). The M-cell pockets also contained occasional cells with cytoplasmic IgA or IgM. These sites thus contained a heterogeneous B-cell population with features of both follicular mantle (sIgD+ sIgM+) and marginal zone (sIgD- sIgM+) B lymphocytes. Adjacent T lymphocytes were generally of the memory phenotype (CD45RO+). Our findings suggest that the M-cell-associated B lymphocytes represent local extensions of B-cell follicles towards the gut lumen, developed topically to facilitate antigen presentation and diversification of mucosal immune responses.

Theiler's virus-induced demyelination in mice immunosuppressed with anti-IgM and in mice expressing the xid gene

Intracerebral infection with Theiler's murine encephalomyelitis virus produces chronic immune-mediated demyelination in susceptible strains of mice. We examined the role of Ig in the pathogenesis of demyelination. In susceptible SJL/J mice (H-2s), suppression of B cell responses with IgG fraction of goat anti-mu (anti-mu IgG) from birth resulted in increased numbers and severity of demyelinating lesions in the spinal cord 35 days after infection. In contrast, treatment of resistant C57BL/10 (H-2b), C57BL/6 (H-2b), or B10.D2 (H-2d) mice with anti-mu IgG had no apparent effect since these mice did not develop demyelination or inflammation in the spinal cord following infection. Similar results were obtained with certain strains of B-cell deficient mice that exhibit the xid gene mutation. Male CBA/NJ (xid) showed increased meningeal inflammation and demyelination compared to male CBA/J mice. However, B6.CBAN, C3.CBAN, or C.CBAn mice showed no or minimal evidence of demyelination despite the presence of the xid mutation. In the SJL/J mouse, the majority of the humoral immune response to virus antigen was restricted to the IgG2b and IgM isotypes. These data indirectly support the hypothesis that immunoglobulins protect partially against development of virus-induced demyelination in susceptible but not resistant animals. In addition, the data argue strongly against the hypothesis that TMEV-induced demyelination is mediated predominantly by humoral autoimmune or humoral viral immune mechanisms.

Studies of the immunological activities of the outer membrane protein from Escherichia coli

The outer membrane protein (OMP) prepared from Escherichia coli was found to be a potent mitogen for murine B cells and to be capable of inducing polyclonal antibody formation as well as a proliferative response. Spleen cells from nude mice responded equally as well to OMP as those from their normal litter-mates, whereas nylon-wool-purified T cells or thymocytes failed to respond. The proliferative response was dependent on the presence of macrophages. The macrophage dependency of the polyclonal antibody response seemed to be less than that of the proliferation. OMP was mitogenic for lipopolysaccharide (LPS)-resistant C3H/HeJ spleen cells, further indicating that OMP is an unique B-cell mitogen distinct from LPS.

OMP also enhanced the specific antibody response sixty-seven-fold to an optimal dose of sheep red blood cells (SRBC) in vitro. The kinetics of the response, however, was not altered from that of cultures without OMP. The anti-SRBC response of spleen cells from C3H/HeJ mice was also enhanced by the addition of OMP, suggesting that the adjuvant effects were not due to the LPS in the preparation. Antibody responses in vitro to TI-1 antigens, trinitrophenyl-LPS (Boivin) (TNP-LPS^B) and TNP-Brucella abortus, were not enhanced in the presence of OMP. In contrast OMP enhanced the response to TI-2 antigens, TNP-LPS^W (Westphal) and dinitrophenyl-Ficoll and T cells were shown to be required for these augmented antibody responses. Enhancement was not seen in nude mouse spleen cell cultures but was seen when nylon-wool-purified T cells were added to the cultures.

Effect of anti-delta antibodies on clonal expansion and maturation of B lymphocytes

The effect of a monoclonal anti-delta antibody on the in vitro B cell response to the B cell mitogen lipopolysaccharide (LPS) has been studied. Titration of anti-delta antibody in mass cultures stimulated by LPS resulted in a dose-dependent reduction of thymidine incorporation. IgM and IgG plaque forming cell (PFC) responses were poorly affected at high concentration, and slightly increased at low concentrations of anti-delta antibody. By limiting dilution analysis it was shown that anti-delta antibody inhibit 30-50% of LPS-reactive B cells to grow as IgM secreting clones, while increasing the average size of clones that grew in the presence of anti-delta as compared to control cultures. Anti-delta also results in increased frequencies of IgG secreting clones. By immunofluorescence it was possible to show the presence of a higher relative number of cells containing immunoglobulin as an effect of anti-delta antibodies. Observations made at early times of culture indicate that the cells that do not proliferate in the presence of anti-delta undergo an early maturation to secretion. Experiments performed on LPS blasts suggest that the effects of anti-delta on cell proliferation require the presence of antibodies at early times in the response, while the effects on maturation can be manifested during clonal development. The relevance of membrane IgD and of the IgM-to-IgD ratio in the maintenance versus exhaustion of the clone is discussed.

Physiology of IgD. I. Compensatory phenomena in B lymphocyte activation in mice treated with anti-IgD antibodies

The role of delta-positive cells in the immune response was studied by comparing the effects of treatment with allotype-specific IgD hybridoma antibody on homozygous BALB/c or SJL/J and heterozygous (BALB x SJL)F1 mice. Homozygous mice, injected from birth with the relevant anti-delta antibody, made primary or secondary immune responses to intravenously injected trinitrophenyl (TNP)-Brucella abortus, TNP-Ficoll, and TNP-keyhole limpet hemocyanin, which did not differ significantly from those of control mice, despite the fact that IgD+ cells were depleted and Ig+ cells were markedly reduced in the spleens of treated mice. Responses in nodes draining a local injection of TNP-Brucella abortus were, however, significantly suppressed. Heterozygous mice, injected from birth with either anti-Ig-5a or anti-Ig-5b, showed a marked reduction in the number cells producing IgG antibody of linked allotype specificity in the secondary response to intravenously injected sheep erythrocytes. A corresponding decrease in the amount of serum IgG2a of that allotype specificity was also noted. However, in agreement with the results obtained in homozygotes, heterozygotes injected simultaneously with anti-IgD directed against each of the allotypes made normal, if not enhanced, plaque-forming cell responses of both allotype specificities. Similarly, serum IgG2a levels were normal in all but one mouse treated in this fashion. These results indicate that IgD+ cells are not essential for an immune response in vivo. Although the delta-positive cell is used preferentially under normal conditions, it appears that an alternative mechanism exists by which, in the absence of these cells, the animal is able to make a normal immune response.