Characterization of human sclera barrier properties for transscleral delivery of bevacizumab and ranibizumab

The objectives of this study were to (a) investigate transscleral permeation of antivascular endothelial growth factor drugs bevacizumab and ranibizumab and (b) examine the effects of molecular structures of macromolecules upon permeation across human sclera using bevacizumab, ranibizumab, fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (FITC-BSA), FITC-labeled ficoll (FITC-ficoll), and FITC-labeled dextrans (FITC-dextrans) in vitro. The hydrodynamic radii of the macromolecules were measured using dynamic light scattering, their partition coefficients to sclera were determined in uptake experiments, and their permeability coefficients and transport lag times across sclera were evaluated in transport experiments of side-by-side diffusion cells. Macromolecules showed relatively low partition coefficients to sclera. The partition coefficient of FITC-BSA was found to be related to its concentration in the equilibration solution, whereas for other macromolecules, no specific concentration dependency was observed. The macromolecules displayed relatively low permeability coefficients and long transport lag times because of their molecular sizes and hindered diffusion. Bevacizumab, ranibizumab, and FITC-BSA exhibited lower transscleral permeability and longer transport lag times than FITC-dextrans and FITC-ficoll of comparable molecular weights possibly because of the flexible structures of the polysaccharides. Thus, the polysaccharides may not be good surrogate permeants to model transscleral transport of therapeutic proteins in transscleral delivery studies.

Dibenzo[def,p]chrysene (DBC) suppresses antibody formation in spleen cells following oral exposures of mice

Dibenzo[def,p]chrysene (DBC) is a potent environmental carcinogen in rodents, fish, and human cells examined in culture. There are numerous similarities between the patterns of cytochrome P-450 (P450) activation of DBC and its covalent binding to DNA and proteins with another polycyclic aromatic hydrocarbon (PAH), 7,12-dimethylbenz[a]anthracene (DMBA). Our lab has previously shown that DMBA produces immunosuppression in rodents and human cell systems. Therefore, the purpose of these studies was to examine the immunotoxicity of DBC in a rodent model that was found to be sensitive to the immunosuppressive effects of DMBA. Data showed that DBC had similar potency to DMBA in producing suppression of a T-dependent antibody response (TDAR) and altered spleen cell subsets in a similar manner as DMBA when DMBA was given by gavage for 5 d in corn oil to mice at doses of 1-100 mg/kg total cumulative doses. T-cell-independent antigen (TNP-Ficoll) responses were quantitatively less sensitive to DBC suppression. It was also found that as with DMBA, DBC produced a persistent immunosuppression, which lasted for at least 4 wk following dosing with a novel pill method for self-administration of DBC. In conclusion, DBC appears to possess many of the same characteristics of DMBA in terms of its immunotoxicity.

Inhibitory effect of the alkaloid warifteine purified from Cissampelos sympodialis on B lymphocyte function in vitro and in vivo

The aqueous fraction of the ethanolic extract of the plant CISSAMPELOS SYMPODIALIS (Menispermaceae) was previously described to inhibit B cell function. The alkaloid warifteine is the major component of this extract. In the present study we investigated the effect of warifteine on B lymphocyte function and characterized its mechanism of action. Purified splenic murine B lymphocytes were stimulated with either Toll-like receptor (TLR) ligands (LPS, Pam (3)Cys and CpG oligodeoxynucleotides) or anti-IgM antibody and the effect of warifteine on B cell response was investigated. Warifteine inhibited both the proliferative response and immunoglobulin (Ig) secretion induced by these stimuli. Kinetics studies demonstrated that warifteine blocked B cell function even when added after 24 h of a 72 h culture. The inhibitory effect of warifteine was also detected in cultures activated by phorbol myristate acetate and calcium ionophore. We investigated the signal transduction pathways blocked by warifteine. It did not modify the total protein phosphorylation pattern in LPS and anti-IgM-stimulated B cell cultures. It did, however, decrease the rise in intracellular calcium levels, the phosphorylation of the mitogen activated protein kinase (MAPK) ERK and the intranuclear levels of the transcription factor NFkappaB. Warifteine also induced an increase in cAMP and its effect on LPS-induced proliferation was mimicked by the control adenyl cyclase activator forskolin. IN VIVO Ig production induced by the TI-2 antigen TNP-ficoll was also inhibited by warifteine. Taking together, our data suggest that warifteine is a potent inhibitor of B cell response both IN VITRO and IN VIVO and that this effect may be due to the induction of increased intracellular cAMP levels, suggesting that this substance may be useful as a modulator of B cell function.

Similarity of permeabilities for Ficoll, pullulan, charge-modified albumin and native albumin across the rat peritoneal membrane

AIM

Compared to neutral globular proteins, neutral polysaccharides, such as dextran, pullulan and Ficoll, appear hyperpermeable across the glomerular filtration barrier. This has been attributed to an increased flexibility and/or asymmetry of polysaccharides. The present study investigates whether polysaccharides are hyperpermeable also across the continuous capillaries in the rat peritoneum.

METHODS

In anaesthetized Wistar rats, FITC-Ficoll or FITC-pullulan together with (125)I-human serum albumin (RISA) or neutralized (125)I-bovine serum albumin (nBSA) were given intravenously, after which peritoneal dialysis (PD) using conventional PD fluid (Gambrosol 1.5%) was performed for 120 min. Concentrations of FITC-polysaccharides and radioactive albumin species in plasma and dialysis fluid were analysed with high-performance size exclusion chromatography and a gamma counter respectively. Transperitoneal clearance values were calculated for polysaccharides in the molecular radius range 36-150 A, and for RISA and nBSA.

RESULTS

Ficoll and pullulan showed more or less identical permeabilities, compared to RISA and nBSA, across the peritoneal membrane. Although RISA-clearance, 5.50 +/- 0.28 (microL min(-1); +/-SEM), tended to be lower than the clearances of Ficoll(36A) (6.55 +/- 0.25), pullulan(36A) (6.08 +/- 0.22) and nBSA (6.56 +/- 0.23), the difference was not statistically significant. This is in contrast to the hyperpermeability exhibited by polysaccharides across the glomerular filtration barrier and also contrasts with the charge selectivity of the latter.

CONCLUSION

The phenomenon of molecular flexibility is more important for a macromolecule's permeability through the glomerular filter than across the continuous peritoneal capillary endothelium. Furthermore, it seems that charge plays a subordinate role in the steady-state transport across the combined peritoneal capillary-interstitial barrier.

Size and charge selectivity of the glomerular filter in early experimental diabetes in rats

Microalbuminuria is an early sign of diabetic nephropathy. The aim of the present study was to investigate whether the changes of the glomerular filtration barrier in early experimental diabetes are due to size- or charge-selective alterations. Wistar rats, made diabetic by streptozotocin (STZ) and having their blood glucose maintained at ∼20 mM for 3 or 9 wk, were compared with age-matched controls. Glomerular clearances of native albumin (Cl-HSA) and neutralized albumin (Cl-nHSA) were assessed using a renal uptake technique. Glomerular filtration rate and renal plasma flow were assessed using51Cr-EDTA and [125I]iodohippurate, respectively. In a separate set of animals, diabetic for 9 wk, and in controls, glomerular sieving coefficients (θ) for neutral FITC-Ficoll (molecular radius: 15–90 Å) were assessed using size exclusion chromatography. At 3 wk of diabetes, Cl-HSA and Cl-nHSA remained unchanged, indicating no alteration in either size or charge selectivity. By contrast, at 9 wk of diabetes, there was a twofold increase of Cl-HSA, whereas Cl-nHSA remained largely unchanged, at first suggesting a glomerular charge defect. However, according to a two-pore model, the number of large pores, assessed from both Ficoll and Cl-HSA, increased twofold. In addition, a small reduction in proximal tubular reabsorption was observed at 3 wk, which was further reduced at 9 wk. In conclusion, no functional changes were observed in the glomerular filtration barrier at 3 wk of STZ-induced diabetes, whereas at 9 wk there was a decrease in size selectivity due to an increased number of large glomerular pores.

Plasma cell differentiation in T-independent type 2 immune responses is independent of CD11c(high) dendritic cells

Dendritic cells (DC) play an important role as antigen-presenting cells in T cell stimulation. Interestingly, a number of recent studies also imply DC as critical accessory cells in B cell activation, isotype switching and plasma blast maintenance. Here we use the conditional in vivo ablation of CD11c(high) DC to investigate the role of these cells in T-independent type 2 immune responses. We show that CD11c(high) DC are dispensable for the initiation and maintenance of a primary immune response against the T-independent type 2 antigen (4-hydroxy-3-nirophenyl)acetyl-Ficoll. Our results suggest that support for plasma cell formation in T cell-independent immune responses can be provided by non-DC such as stromal cells, or is independent of external signals. Interestingly, we found plasma blasts to express CD11c and to be diphtheria toxin-sensitive in CD11c-diphtheria toxin receptor-transgenic mice, providing a unique tool for future analysis of in vivo aspects of plasma cell biology.

Genistein suppresses antigen-specific immune responses through competition with 17beta-estradiol for estrogen receptors in ovalbumin-immunized BALB/c mice

OBJECTIVE

The aim of this study was to determine the effects of phytoestrogen genistein on antigen (Ag)-specific immune responses and elucidate the mechanisms underlying those effects.

METHODS

Ovalbumin (OVA)-immunized BALB/c mice were administered genistein for 35 d, and OVA-specific immune responses were examined by measuring OVA-specific proliferative responses, production of cytokines, and antibody responses. To assess the effect of genistein on antibody responses to thymus-independent Ag, mice were immunized with 2,4,6-trinitrophenyl (TNP)-Ficoll instead of OVA. Effect of genistein on the functions of CD11c(+) dendritic cells was also examined. Finally, to determine the contribution of estrogen receptor to genistein-mediated immune regulation, mice that had been administered genistein were treated with the estrogen receptor antagonist ICI 182,780 and OVA-specific proliferative responses were examined.

RESULTS

OVA-specific proliferative responses and interferon-gamma production levels were decreased in mice administered 20 mg/kg genistein compared with those in control mice without reduction in responses to anti-CD3 monoclonal (m)antibody. The level of OVA-specific immunoglobulin (Ig)G1 was also decreased in mice administered genistein. Levels of OVA-specific IgG2a and IgG2b production and interleukin-4 production in response to OVA were not significantly different but tended to decrease in genistein-treated mice. Genistein administration did not influence the TNP-specific IgM and IgG levels. Furthermore, genistein did not affect the Ag-presenting activity of CD11c(+) dendritic cells. Treatment with ICI 182,780 decreased OVA-specific proliferative responses, but genistein did not suppress these responses synergistically in mice treated with ICI 182,780.

CONCLUSIONS

The results of this study suggest that genistein suppresses Ag-specific immune responses. The mechanism underlying the suppression is responsible for the competition of genistein with endogenous 17beta-estradiol for estrogen receptors.

Transvascular protein transport in mice lacking endothelial caveolae

Caveolae are Ω-shaped vesicular structures postulated to play a role in transvascular protein transport. Studies on mice lacking endothelial caveolae, caveolin-1 knockout (Cav-1-KO) mice, indicate increased macromolecular transport rates. This was postulated to be due to the appearance of an alternative pathway. The present study tested whether an alternative pathway had appeared in Cav-1-KO mice. Male Cav-1-KO ( n = 12) and male control mice ( n = 13) were intubated and anesthetized using 2% isoflurane.125I-labeled albumin,131I-labeled immunoglobulin M (IgM), and polydisperse FITC-Ficoll were administered intravenously. During tracer administration, a 90-min peritoneal dialysis dwell was performed. Clearance of tracers to dialysate and permeability-surface area product for glucose were assessed. Transvascular protein transport was higher in Cav-1-KO compared with control mice. Albumin clearance from plasma to peritoneum was 0.088 ± 0.008 μl/min in control and 0.179 ± 0.012 μl/min in Cav-1-KO ( P = 0.001) mice. IgM clearance was 0.049 ± 0.003 and 0.083 ± 0.010 μl/min in control and Cav-1-KO mice, respectively ( P = 0.016). Ficoll clearance was increased in Cav-1-KO mice. In conclusion, the lack of caveolae in Cav-1-KO mice resulted in a marked increase in macromolecular transport. A two-pore analysis of the Ficoll clearance data revealed that the higher transport rate in Cav-1-KO mice was not compatible with the appearance of an alternative pathway for macromolecular transport. In contrast, the higher transperitoneal protein and Ficoll clearance is consistent with passive porous transport through an unperturbed two-pore system, presumably at an elevated capillary hydraulic pressure. Alternatively, the data may be explained by reductions in the selectivity of the endothelial glycocalyx, leading to an increased capillary hydraulic conductivity and large solute filtration.

A novel role for caveolin-1 in B lymphocyte function and the development of thymus-independent immune responses

Caveolin-1 (Cav-1) functions as a scaffold or platform for many molecules involved in signal transduction. However, the expression and function of Cav-1 in the immune system has been controversial. Here, we show that Cav-1 mRNA and protein is indeed expressed in murine B-lymphocytes in a regulated mannerin response to LPS. Cav-1 deficient mice displayed reduced levels of antibody in their serum. In order to examine the role of Cav-1 in the development of immunoglobulin-mediated immune responses, we immunized wild-type and Cav-1 deficient mice with thymus-dependent and thymus independent antigens. Our results show that Cav-1 deficient mice have a normal response to thymus-dependent antigens, but have a reduced response to both type I and type II thymus independent antigens. However, lymphocyte populations in the spleen and peritoneum were not altered and no changes were observed in splenic architecture. Caveolin-1 deficient B-lymphocytes did not display altered proliferation in response to different stimuli. However, we found that Cav-1 deficient B cells have reduced IgG(3) secretion in vitro in response to LPS. Finally, we also demonstrate that human plasma cells (mature B lymphocytes) express Cav-1 in vivo. Taken, together these results provide convincing evidence for the expression of Cav-1 in activated B-lymphocytes and demonstrate a role for Cav-1 in the development of thymus-independent immune responses.

[A correlation between respiration and synthesis of ATP in mitochondria at different degree of uncoupling of oxidative phosphorylation]

It is known that mitochondrial respiration in state 3 is due to three simultaneous and independent processes: synthesis of ATP (1), endogenous passive proton leakage (2), and proton leakage by protonophoric uncoupler (3). The total rate of processes (2) and (3) is equal to the product of respiration rate in state 4 and coefficient KR, which is defined as the ratio of the deltamuH+ value in state 3 to that in state 4. It is shown that it is possible to calculate both the rates of processes (1), (2) and (3) separately and the protonophoric activity of uncoupler using the coefficient KR and other coefficients, which are determined as the ratio of deltamuH+ values in state 3 or in state 4 to its maximal value. Simple methods of determination of these coefficients were developed, which are based on the study of the dependence of respiration rate in states 3 and 4 on the concentration of protonophoric uncoupler. It was found that the uncoupling action of palmitate, a natural uncoupler of oxidative phosphorylation, unlike classic uncoupler-protonophores DNP and FCCP, depends not only on its protonophoric activity but also on the inhibition of the process (1).

B cell hyperresponsiveness and expansion of mature follicular B cells but not of marginal zone B cells in NFATc2/c3 double-deficient mice

Marginal zone (MZ) B cells and peritoneal B-1 cells provide a first defense system of thymus-independent Ab responses against foreign pathogens and therefore share a number of functional properties. Recently, development of B-1a cells was shown to be controlled by the transcription factor NFATc1. We show here that mice deficient for NFATc2 and c3 display a distinct lower representation of MZ B cells, which is correlated with a reduced capturing of trinitrophenyl-Ficoll. In contrast, mature follicular B cells from NFATc2/c3-/- mice are strongly increased in number. NFATc2/c3-/- B cells exhibit a marked increase in BCR-induced intracellular Ca2+ mobilization and proliferation. However, trinitrophenyl-Ficoll-specific IgM and IgG3 responses of NFATc2/c3-deficient mice are intact, and chimeric mice reconstituted with NFATc2/3-deficient B cells show a normal number of MZ B cells and normal BCR responses. These observations suggest that the strongly elevated Th2 cytokine milieu in NFATc2/c3-deficient mice leads to a hyperactivation of mature, follicular B cells, whereas MZ B cells are less responsive to these signals.

Concentration-dependent bifunctional effect of TGF-beta 1 on immunoglobulin production: a role for Smad3 in IgA production in vitro

Injury to the liver results in rapid induction of transforming growth factor-beta1 (TGF-beta(1)) consistent with a role for TGF-beta(1) in repairing damaged tissue. In addition to its ubiquitous role in injury repair, TGF-beta(1) is also well established as a critical regulator of immune homeostasis; however, its mechanisms of action remain enigmatic. We have previously demonstrated that the hepatotoxic chlorinated hydrocarbon, carbon tetrachloride, suppresses helper T-lymphocyte function in a TGF-beta(1)-dependent manner. Here, we report that, in opposition to its immunosuppressive effects at picomolar concentrations, femtomolar concentrations of TGF-beta(1) augment T cell-dependent anti-sRBC IgM antibody forming cell (AFC) and T cell-independent DNP-Ficoll-induced AFC responses. These data support a concentration-dependent bifunctional effect by TGF-beta(1) on humoral immune responses in vitro. We further investigated a putative mechanistic role for Smad3, an intracellular mediator of TGF-beta(1) signaling, in propagating the inhibitory effects of TGF-beta(1) on humoral immune responses. Relative to wild type littermates, splenocytes from mice homologous for a null mutation in the gene encoding the TGF-beta receptor-activated Smad3 (Smad3(Exon8-/-)) were less sensitive to inhibition by TGF-beta(1) following anti-sRBC- and LPS-sensitization in vitro. In agreement, inhibition of IgM protein production by TGF-beta(1) was also dampened in LPS-sensitized Smad3(Exon8-/-) splenic B cells. Moreover, stimulation of IgA by TGF-beta(1) was abrogated in LPS-sensitized Smad3(Exon8-/-) splenocytes suggesting an additional role for Smad3 in regulating IgA production in vitro. Our results suggest that the effects of TGF-beta(1) on humoral immune responses fundamentally differ in a concentration-dependent manner and are mediated, in part, through Smad3 signaling.

Anomalous fractional clearance of negatively charged Ficoll relative to uncharged Ficoll

Recent studies, using low-temperature perfusion of rat kidneys, have claimed the existence of renal charge selectivity simply on the basis of the differential excretion rates of uncharged Ficoll and charged proteins. To test for the existence of charge selectivity in vivo, we examined the clearance of negatively charged Ficoll compared with uncharged Ficoll. A short-term approach to steady state was used to study the fractional clearances. Relative clearances were also examined using an osmotic pump technique where the tracers reach a steady-state value in conscious rats after 7 days. Carboxymethyl Ficoll was stable during filtration and renal passage, was not taken up by the kidneys, and did not bind to plasma proteins. There was no significant difference in the fractional clearance of molecules with radius of 36 A for Ficoll (fractional clearance = 0.048 +/- 0.038, n = 5) and negatively charged carboxymethyl Ficoll (fractional clearance = 0.028 +/- 0.019, n = 5). For molecules with radii greater than 36 A, carboxymethyl Ficoll had facilitated clearance with respect to uncharged Ficoll [for example, at a radius of 60 A fractional clearance for Ficoll = 0.0012 +/- 0.0005 (n = 5), whereas that for carboxymethyl Ficoll = 0.015 +/- 0.005 (n = 5)]. Renal function was not compromised by carboxymethyl Ficoll as uncharged Ficoll in urine exhibited similar hydrodynamic size profiles when studied in the presence of excess unlabeled carboxymethyl Ficoll. The facilitated clearance of negatively charged Ficoll with respect to uncharged Ficoll reveals a property of the capillary wall, which has been previously observed with other nonproteinaceous polyanions. This study demonstrates that the glomerular capillary wall is not charge selective in the form of excluding negatively charged Ficoll. However, the charge properties of the capillary wall may influence the facilitated transport of charged Ficoll compared with uncharged Ficoll.

T-bet regulates T-independent IgG2a class switching

The IgG2a Ig subclass plays a critical role in the pathogenesis of humoral autoimmunity and protection against pathogens. The T-box transcription factor T-bet has been implicated as a critical mediator of class-switch recombination (CSR) to IgG2a, but its relative importance to this process in various immune contexts remains incompletely defined. We report here that, surprisingly, T-bet is selectively required for IgG2a class switching in response to T-independent, but not T-dependent, stimuli. Specifically, T-dependent signaling through CD40, in contrast to T-independent signaling via lipopolysaccharide, can bypass a requirement for T-bet in IgG2a germline transcription and subsequent isotype switching. In contrast, T-bet-deficient B cells undergo class switching to other IgG isotypes at least as well as wild-type counterparts. Thus, T-bet is a class-specific regulator of IgG CSR and represents a unique regulator of B cell differentiation by participating in a T-independent, but not a T-dependent, activation pathway. T-bet-deficient B cells therefore represent a novel paradigm by which to investigate the regulation of humoral immune responses.

Glomerular size and charge selectivity in the mouse after exposure to glucosaminoglycan-degrading enzymes

This is the first functional study of glomerular size and charge selectivity in mice. The aim was to investigate the controversial issue of glomerular permselectivity in animals exposed to glucosaminoglycan-degrading enzymes, hyaluronidase, and heparinase. Fractional clearances (theta) for FITC-Ficoll and albumin were estimated in isoflurane anesthetized mice in vivo and in cooled isolated perfused kidneys (cIPK). In cIPK, a significant increase of theta(albumin) from 0.0023 (95% confidence interval, 0.0014 to 0.0033) in controls to 0.0130 (95% confidence interval, 0.0055 to 0.0206) was seen after hyaluronidase treatment. The theta for neutral Ficoll of similar size as albumin was 0.063 to 0.093 in all groups. According to a heterogeneous charged fiber model, the fiber volume fraction of negatively charged fibers decreased by 10% after enzyme treatments. It is concluded that glomerular size and charge selectivity in mice is similar to that previously shown for rats. Moreover, hyaluronic acid, chondroitin sulfate, and heparan sulfate are of importance for charge selectivity.

Antibody production in early life supported by maternal lymphocyte factors

To examine the influence of maternal lymphocyte factors on the immune responses in offspring in early life, antibody production in neonates born to either normal or lymphocyte-deficient mothers was analyzed. Recombination activating gene (Rag)-2(+/-) mouse neonates born to Rag-2(+/+), Rag-2(+/-)or Rag-2(-/-)mothers were injected with goat anti-mouse IgD antiserum, and IgE and IgG(1) production was evaluated. The levels of IgE and IgG(1) were higher in the pups born to Rag-2(+/+)and Rag-2(+/-) dams than to lymphocyte-deficient Rag-2(-/-) dams. The enhanced antibody production in the former compared with the latter neonates was also found following immunization with ovalbumin or TNP-Ficoll. Thus, the presence of maternal lymphocyte factors was suggested in neonates that augmented antigen-specific antibody production in both T cell-dependent and -independent pathways. A reduction in antibody production was observed in normal neonates when they were foster-nursed by Rag-2(-/-) mothers. Thus, the maternal lymphocyte factors enhancing the immune responses in newborns were shown to be present in breast-milk.

Incomplete block of B cell development and immunoglobulin production in mice carrying the muMT mutation on the BALB/c background

The expression of the preB cell receptor (preBCR), composed of the mu chain, surrogate light chains and the Igalpha /Igbeta signal transduction unit, permits further differentiation of Bcell precursors. C57BL/6 mice homozygous for an inactivating mutation of the membrane exon of the mu chain gene (C57BL/6muMT/muMT)) cannot form a preBCR and are, consequently, devoid of mature B lymphocytes. Here we present evidence that the block of B cell development by the muMT mutation is incomplete in BALB/c mice. Unlike C57BL/6muMT/muMT), BALB/cmuMT/muMT) mice generate small numbers of mature B cells, accumulate plasma cells and produce high levels of all immunoglobulin isotypes, except IgM. The observed phenomenon seems to be controlled by a single genetic locus that is not linked to IgH.

BOB.1/OBF.1 deficiency affects marginal-zone B-cell compartment

Marginal-zone (MZ) B cells represent a first line of defense against particulate blood-borne antigens. Together with the B1 cells, they are responsible for the early response against type II T-independent antigens. The molecular pathways controlling the development of MZ B cells are only poorly understood. We found that these cells are virtually absent in mice deficient in the BOB.1/OBF.1 coactivator. Loss of these B cells was demonstrated by the lack of cells showing the appropriate cell surface phenotype but also by histological analyses and tri-nitro-phenol-Ficoll capturing. The lack of these cells is a B-cell-intrinsic defect, as shown by bone marrow complementation experiments. We also show that the expression of BOB.1/OBF.1 in peripheral B cells is required for the development of MZ B lymphocytes. Our analysis of BOB.1/OBF.1-deficient splenic B cells reveals alterations in cell motility, tumor necrosis factor receptor expression, and B-cell receptor (BCR) signaling. These changes could contribute to the loss of MZ B lymphocytes by altering the maturation of the cells. Interestingly, development of and BCR signaling in B1 B cells are completely normal in BOB.1/OBF.1 mutant mice.

BALB/c mice orally pretreated with diclofenac have augmented and accelerated PLNA responses to diclofenac

The nonsteroidal anti-inflammatory drug (NSAID) diclofenac (DF) is associated with idiosyncratic hepatotoxicity and several other distinct hypersensitivity reactions. The mechanism(s) are unknown but evidence suggests both cell-mediated and antibody-mediated immune effector systems may be involved. In the present studies, the immunostimulating potential of DF was evaluated using the direct and TNP-Ficoll (trinitrophenyl (TNP)-Ficoll) popliteal lymph node assays (PLNA). These assays were conducted in naive mice, T-cell-deficient mice, or in mice that had been pretreated with a single oral dose of DF. In naive mice, DF induced a dose-, and time-dependent reaction in the direct PLNA. A significant increase in popliteal lymph node (PLN) weight and PLN cellularity was detected 7 days after the injection of 0.50 and 0.75 mg DF, whereas 0.25 mg DF produced no observable effect. With 0.75 mg, there was a rapid accumulation of cells in the PLN between days 5 and 6, with maximum PLN cellularity observed between days 7 and 10. The immunostimulating effects of DF were significantly attenuated in T-cell-deficient mice. In the TNP-Ficoll PLNA conducted in naive mice, DF caused a dose-dependent increase in PLN cellularity on day 7 with a time-dependent increase in anti-TNP antibody forming cells (AFCs) in the PLN; the reaction was dominated by IgM anti-TNP AFCs from day 4 through day 7, but IgG1 anti-TNP AFCs and IgG3 anti-TNP AFCs were detected beginning on day 5 and day 6, respectively. Relative to mice pretreated with vehicle (ddH2O), mice orally pretreated with DF had a significantly greater increase in PLN weight 5 days following the injection of 0.25 mg DF and a significantly greater increase in PLN weight and cellularity 4 days following the injection of 0.50 mg DF. Oral pretreatment with DF had no observable effect on the direct PLN reaction induced following the footpad injection of the irrelevant drugs, D-penicillamine (D-PEN) or streptozotocin. When 0.50 mg DF was co-injected with TNP-Ficoll, mice orally pretreated with DF, compared to vehicle-pretreated mice, and had a significantly greater increase in IgM anti-TNP AFCs on day 4, and a significant increase in both IgG1 and IgG3 anti-TNP AFCs on day 7. Additionally, IgG1 anti-TNP AFCs were detected in the PLN of DF-pretreated mice as early as day 4. No differences in anti-TNP AFCs were detected when orally pretreated mice were injected with 0.50 mg D-PEN. Collectively, these results demonstrated that DF (i) is an immunostimulating drug that induced a dose-, time- and T-cell-dependent PLN reaction in naive mice, (ii) provided non-cognate help that produced antibody against co-injected TNP-Ficoll, and (iii) mice orally pretreated with DF had DF-specific increased responsiveness in the direct PLNA, which (iv) resulted in accelerated and augmented AFC production against co-injected TNP-Ficoll. These novel findings suggest that oral administration of DF may result in primed T cells that respond with footpad injection. Thus, the oral pretreatment modification of the PLNA should be further explored as a possible alternative to hypersensitivity testing with drugs administered via the oral route. Additional studies with other compounds known to produce hypersensitivity reactions are needed.

Generation of adult-like antibody avidity profiles after early-life immunization with protein vaccines

The capacity to induce high-avidity antibodies following early-life immunization has long been questioned, and the possibility of inducing such antibodies soon after birth is a recognized goal for a number of vaccination strategies. Therefore, we assessed the capacity to develop high-avidity antibodies to peptidic vaccines in 1-week-old BALB/c mice. The dynamics of the generation of antibody molecules of increasing avidity were analyzed on circulating serum antibodies and, where feasible, at the single-cell level on spleen and bone marrow antibody-secreting cells. Two alum-adsorbed protein-based human vaccines, tetanus toxoid (TT) and pertussis toxin, induced neonatal antibody responses with adult-like avidity profiles. This was confirmed at the level of spleen and bone marrow ASC. In contrast, immunization with TT-P30, a 21-mer synthetic peptide containing a TT-immunodominant epitope, trinitrophenyl hapten (TNP) conjugated to ovalbumin or TNP conjugated to Ficoll, induced a much lower avidity profile in early life than in adults. These observations indicate that in murine models the avidity maturation of T cell-dependent antibody responses induced by structurally complex protein vaccines can be fully elicited after early life immunization, as opposed to the maturation of responses induced with short peptides or hapten-based vaccines.

Reduction of marginal zone B cells in CD22-deficient mice

CD22 is a B cell-specific member of the immunoglobulin superfamily and binds to sialic acid. CD22 inhibits B cell receptor signaling. Mice deficient for CD22 show a largely normal B cell development. Here, we have performed a detailed analysis of the splenic B cell population and found that the subset of marginal zone (MZ) B cells was selectively reduced in CD22-deficient mice. CD22-deficient mice showed a lack of TNP-ficoll capturing cells in the MZ and a reduced response to TNP-ficoll, particularly when the antigen was applied intravenously. CD22-deficient B cells showed both enhanced motility as well as enhanced chemotaxis to certain chemokines. The altered chemokine responsiveness or the higher signaling capacity of CD22-deficient B cells may lead to the compromised MZ B cell compartment, as both processes have previously been shown to affect MZ composition.

Interleukin-1 beta, but not interleukin-1 alpha, is required for T-cell-dependent antibody production

Interleukin-1 (IL-1) consists of two molecules, IL-1 alpha and IL-1 beta, and IL-1 receptor antagonist (IL-1Ra) is a natural inhibitor of these molecules. Although the adjuvant effects of exogenously administered IL-1 in the humoral immune response are well known, the roles of endogenous IL-1 and the functional discrimination between IL-1 alpha and IL-1 beta have not been elucidated completely. In this report, we investigated the role of IL-1 in the humoral immune response using gene-targeted mice. Both primary and secondary antibody production against T-dependent antigen, sheep red blood cells (SRBC), was significantly reduced in IL-1 alpha/beta-/- mice, and was enhanced in IL-1Ra-/- mice. The intrinsic functions of B cells, such as antibody production against type 1 T-independent antigen, trinitrophenyl-lipopolysaccharide and proliferative responses against mitogenic stimuli, were normal in IL-1 alpha/beta-/- mice. The proliferative response of T cells and cytokine production upon stimulation with anti-CD3 monoclonal antibody were also normal, as was the phagocytotic ability of antigen-presenting cells (APCs). However, SRBC-specific proliferative response and cytokine production of T cells through the interaction with APCs were markedly impaired in IL-1 alpha/beta-/- mice, and enhanced in IL-1Ra-/- mice. Moreover, we show that SRBC-specific antibody production was reduced in IL-1 beta-/- mice, but not in IL-1 alpha-/- mice. These results show that endogenous IL-1 beta, but not IL-1 alpha, is involved in T-cell-dependent antibody production, and IL-1 promotes the antigen-specific T-cell helper function through the T-cell-APC interaction.

Bullatacin, a potent antitumor annonaceous acetogenin, inhibits proliferation of human hepatocarcinoma cell line 2.2.15 by apoptosis induction

Bullatacin, isolated from the fruit of Annona atemoya, is one of the most potentially effective antitumor annonaceous acetogenins. Bullatacin was studied here for its ability to inhibit the proliferation of 2.2.15 cells, hepatitis B virus (HBV) DNA transfected human hepatocarcinoma cell line. It was found that bullatacin induced cytotoxicity of 2.2.15 cells in a time- and dose-dependent manner. Fifty percent effective dose (ED50) on day 1 of exposure to bullatacin were 7.8 +/- 2.5 nM for 2.2.15 cells. [3H]-Thymidine incorporation assays showed almost the same results. Bullatacin-treatment also reduced concentrations of hepatitis B surface antigen (HBsAg) in the cultured medium released from 2.2.15 cells, coincident with the decrease in the cell proliferation. Analysis of mophological changes of bullatacin-treated 2.2.15 by inverted phase-contrast microscope and eletron microscopy revealed a possible model of action for bullatacin to inhibit proliferation of 2.2.15 cells by inducing apoptosis. Most of the bullatacin-induced cell death was found to be due to apoptosis, as determined by double staining with fluorescein-isothiocyanate (FITC)-labeled annexin V and propidium iodide (PI).

Cytoplasmic segment interactions in the alpha1-subunit of the rat Na+, K+-atpase

The currently accepted topographical model for the organization of the alpha-subunit of the Na+, K+-ATPase in the membrane considers that the protein has ten transmembrane segments and six cytoplasmic loops. Evidence of interaction between the cytoplasmic regions may contribute to a better understanding of the structure/function relationship of this protein. In this study, the first four cytoplasmic segments (C1, C2, C3 and C4) of the rat alpha1 subunit were expressed in Escherichia Coli. The large cytoplasmic loop between transmembrane segments four and five (C3) retained its native structure as demonstrated by the ability of ATP to protect against chemical modification by Fluorescein 5-isothiocyanate (FITC). Interaction studies were conducted by an overlay assay (Far Western blots) and surface plasmon resonance technology. We observed that C3 interacts with the N-terminal segment of the Na+, K+-ATPase, C1; and that both C1 and C3 interact with the cytoplasmic segments C2 and C4.

Inappropriate expression of IgD from a transgene inhibits the function of antigen-specific memory B cells

IgD expression has been shown to be downmodulated upon mitogenic or antigenic activation of B cells. To investigate whether this decrease is of functional significance we studied a mouse strain that expresses transgenic IgD on all B cells. The rearranged gene encoding the heavy chain of this IgD requires endogenous gene rearrangement before it can be expressed; therefore, normal B cell development is not affected. As a result, both transgenic IgD and endogenous IgM and IgD are expressed on all peripheral B cells. We show that the presence of extraneous IgD does not affect normal B cell activation by polyclonal stimulators, nor does it affect the primary IgM or IgG responses to TI or TD antigens. However, the secondary memory response is significantly diminished. The decrease is not attributable to a defective generation of memory B cells; instead the activation of memory cells appears to be compromised. Since the depressed response can be overcome by prior aggregation of the transgenic IgD with allotype-specific anti-IgD antibodies, it appears that persistence of the transgenic IgD on memory cells may influence their ability to be activated. Thus, the decrease in IgD expression on normal B cells after activation may be necessary for optimal activation of memory cells.

ICOS is essential for effective T-helper-cell responses

The outcome of T-cell responses after T-cell encounter with specific antigens is modulated by co-stimulatory signals, which are required for both lymphocyte activation and development of adaptive immunity. ICOS, an inducible co-stimulator with homology to CD28, is expressed on activated, but not resting T cells, and shows T-cell co-stimulatory function in vitro. ICOS binds specifically to its counter-receptor B7RP-1 (refs 5,6,7), but not to B7-1 or B7-2. Here we provide in vivo genetic evidence that ICOS delivers a co-stimulatory signal that is essential both for efficient interaction between T and B cells and for normal antibody responses to T-cell-dependent antigens. To determine the physiological function of ICOS, we generated and characterized gene-targeted ICOS-deficient mice. In vivo, a lack of ICOS results in severely deficient T-cell-dependent B-cell responses. Germinal centre formation is impaired and immunoglobulin class switching, including production of allergy-mediating IgE, is defective. ICOS-deficient T cells primed in in vivo and restimulated in vitro with specific antigen produce only low levels of interleukin-4, but remain fully competent to produce interferon-gamma.

Adjuvant effects of CpG oligodeoxynucleotides on responses against T-independent type 2 antigens

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) are potent in vitro B-cell activators and they have been successfully used to increase in vivo antibody responses to T-dependent peptide and protein antigens. In contrast, the use of CpG-ODN to enhance in vivo antibody responses to various T-independent type 2 (TI-2) antigens has recently generated contradictory results. In this study, we compared the CpG-ODN stimulatory effect on antibody responses of adult and young BALB/c mice to trinitrophenylaminoethyl-carboxymethyl (TNP) -Ficoll and to polysaccharides (PS) from several distinct serotypes of Streptococcus pneumoniae (SPn). CpG-ODN co-administration significantly enhanced antigen-specific immunoglobulin M (IgM), IgG, IgG1 and IgG2a titres to TNP-Ficoll. The depletion of CD4+ cells by monoclonal antibodies (GK1.5) identified their essential role in CpG-ODN-mediated enhancement of antibody responses. In contrast to TNP-Ficoll, CpG-ODN failed to enhance IgM and IgG responses to any of the 18 SPnPS serotypes tested. Providing T-cell epitopes by the conjugation of SPnPS to the carrier protein tetanus toxoid again allowed CpG-ODN to mediate enhancement of IgG, IgG2a and IgG3 responses to most SPnPS serotypes. Thus, antigen-presenting cell/T-cell interaction appears to largely mediate the in vivo influence of CpG-ODN on antibody responses to TI-2 antigens. In early life, additional factors limit CpG-ODN modulation of antibody responses to TI-2 antigens.

Genetic analyses of NFKB1 and OCA-B function: defects in B cells, serum IgM level, and antibody responses in Nfkb1-/-Oca-b-/- mice

Defined patterns of gene expression during cell differentiation are likely to be ensured by multiple factors playing redundant roles. By generating mice deficient in both NFKB1 and OCA-B, we show here that the two transcription factors are required for B-1 cell differentiation and serum IgM production. In addition, relative to Nfkb1(-/-) or Oca-b(-/-) mice, the Nfkb1(-/-)Oca-b(-/-) mice show a decrease in conventional B cell frequencies in the spleen and augmented reductions in T-independent and T-dependent Ab responses. These results suggest that NFKB1 and OCA-B play compensatory roles in multiple aspects of B cell differentiation.

Commitment of B lymphocytes to a plasma cell fate is associated with Blimp-1 expression in vivo

B lymphocyte-induced maturation protein-1 (Blimp-1) is a transcriptional repressor that is sufficient to trigger terminal differentiation in the B cell lymphoma BCL-1. In this study, we have determined the expression pattern of Blimp-1 in vivo in primary and secondary lymphoid organs of humans and immunized mice. Blimp-1 is expressed in plasma cells derived from either a T-independent or T-dependent response in plasma cells that have undergone isotype switching and those resulting from secondary immunization. Blimp-1 is also present in long-lived plasma cells residing in the bone marrow. However, Blimp-1 was not detected in memory B cells. This expression pattern provides further evidence of a critical role for Blimp-1 in plasma cell development, supporting earlier studies in cultured lines. Significantly, Blimp-1 was also found in a fraction (4-15%) of germinal center B cells in murine spleen and human tonsils. Blimp-1 expression in the germinal center is associated with an interesting subset of cells with a phenotype intermediate between germinal center B cells and plasma cells. In the mouse, Blimp-1(+) germinal center B cells peak at day 12 postimmunization and disappear soon thereafter. They are not apoptotic, some are proliferating, they express germinal center markers peanut agglutinin or CD10 but not Bcl-6, and most express CD138 (syndecan-1), IRF4, and cytoplasmic Ig. Together, these data support a model in which B cell fate decisions occur within the germinal center and Blimp-1 expression is critical for commitment to a plasma cell, rather than a memory cell, fate.

Cutting edge: essential role of phospholipase C-gamma 2 in B cell development and function

Cross-linking of the B cell Ag receptor (BCR) induces the tyrosine phosphorylation of multiple cellular substrates, including phospholipase C (PLC)-gamma 2, which is involved in the activation of the phosphatidylinositol pathway. To assess the importance of PLC-gamma 2 in murine lymphopoiesis, the PLC-gamma 2 gene was inducibly ablated by using IFN-regulated Cre recombinase. Mice with a neonatally induced loss of PLC-gamma 2 function displayed reduced numbers of mature conventional B cells and peritoneal B1 cells and defective responses in vitro to BCR stimulation and in vivo to immunization with thymus-independent type II Ags. In contrast, T cell development and TCR-mediated proliferation were normal. Taken together, PLC-gamma 2 is a critical component of BCR signaling pathways and is required to promote B cell development.

Targeted inactivation of the tetraspanin CD37 impairs T-cell-dependent B-cell response under suboptimal costimulatory conditions

CD37 is a membrane protein of the tetraspanin superfamily, which includes CD9, CD53, CD63, CD81, and CD82. Many of these molecules are expressed on leukocytes and have been implicated in signal transduction, cell-cell interactions, and cellular activation and development. We generated and analyzed mice deficient for CD37. Despite the high expression of CD37 on cells of the immune system, no changes in development and cellular composition of lymphoid organs were observed in mice lacking CD37. Analyses of humoral immune responses revealed a reduced level of immunoglobulin G1 (IgG1) in the sera of nonimmunized mice and an alteration of responses to T-cell-dependent antigens. Antibody responses to model antigen administered in the absence of adjuvant and to viral infections were generally poor in CD37-deficient mice. These poor antibody responses could be overcome by the immunization of antigen together with adjuvant. These results suggest a role for CD37 in T-cell-B-cell interactions which manifests itself under suboptimal costimulatory conditions.

Glomerular size and charge selectivity in the rat as revealed by FITC-ficoll and albumin

The fractional clearances (theta) for FITC-Ficoll and albumin were estimated in isolated perfused rat kidneys in which the tubular activity was inhibited by low temperature (8 degrees C) and/or 10 mM NH(4)Cl. The Ficoll data were analyzed according to a two-pore model giving small and large pore radii of 46 A and 80-87 A, respectively. The estimated negative charge density was 35-45 meq/l at 8 degrees C. Perfusion with erythrocyte-free solutions of kidneys at 37 degrees C reduced glomerular size and charge permselectivity. Thus the large pore fraction of the glomerular filtrate (f(L)) was 1.64% at 37 degrees C compared with 0.94% at 8 degrees C. The theta for albumin was four times higher at 37 degrees C than at 8 degrees C (0.86% vs. 0.19%, respectively). NH(4)Cl caused further irreversible damage to the glomerular barrier. We conclude that there are no deleterious effects on the glomerular barrier of a reduction in temperature from 37 degrees C to 8 degrees C. Therefore our data seem to disprove the hypothesis of low glomerular permselectivity and transtubular uptake of intact albumin and support the classic concept of a highly selective glomerular barrier.

Absence of lipopolysaccharide high-dose paralysis in B-cell responses: implications for the one-signal theory

Over 20 years ago, Coutinho and Möller reported that high concentrations of LPS were paralytic for the development of antibody secreting cells (ASC). This data was used to explain bell-shaped dose-response curves observed for antihapten antibody formation in response to haptenated LPS. In turn, this bell curve was used to formulate the one-signal model of B cell activation, which argued that antigen signalling was generally unimportant to B cell responses. The present paper re-examines LPS dose-response curves and finds results that do not support the view that high doses of LPS inhibit B cell differentiation to ASC. If high-dose paralysis is not an attribute of LPS stimulation, then the bell-shaped dose curve for hapten-specific ASC originally observed by Coutinho and Möller required an alternative explanation. Through the use of haptenated Ficoll, it was possible to show that the generation of LPS-induced antitrinitrophenol ASC could be inhibited by antigen presented on an inert substrate. Thus, the transmission of surface Ig-mediated (antigen) signals at higher concentrations can explain the antihapten bell-shaped dose curves, in contradiction to the conclusions of the one-signal model.

A dual role for Src homology 2 domain-containing inositol-5-phosphatase (SHIP) in immunity: aberrant development and enhanced function of b lymphocytes in ship -/- mice

In this report, we demonstrate that the Src homology 2 domain-containing inositol-5-phosphatase (SHIP) plays a critical role in regulating both B cell development and responsiveness to antigen stimulation. SHIP(-/-) mice exhibit a transplantable alteration in B lymphoid development that results in reduced numbers of precursor B (fraction C) and immature B cells in the bone marrow. In vitro, purified SHIP(-/)- B cells exhibit enhanced proliferation in response to B cell receptor stimulation in both the presence and absence of Fcgamma receptor IIB coligation. This enhancement is associated with increased phosphorylation of both mitogen-activated protein kinase and Akt, as well as with increased survival and cell cycling. SHIP(-/)- mice manifest elevated serum immunoglobulin (Ig) levels and an exaggerated IgG response to the T cell-independent type 2 antigen trinitrophenyl Ficoll. However, only altered B cell development was apparent upon transplantation into nonobese diabetic-severe combined immunodeficient (NOD/SCID) mice. The in vitro hyperresponsiveness, together with the in vivo findings, suggests that SHIP regulates B lymphoid development and antigen responsiveness by both intrinsic and extrinsic mechanisms.

Anti-4-1BB monoclonal antibodies abrogate T cell-dependent humoral immune responses in vivo through the induction of helper T cell anergy

The 4-1BB receptor (CDw137), a member of the tumor necrosis factor receptor superfamily, has been shown to costimulate the activation of T cells. Here we show that anti-mouse 4-1BB monoclonal antibodies (mAbs) inhibit thymus-dependent antibody production by B cells. Injection of anti-4-1BB mAbs into mice being immunized with cellular or soluble protein antigens induced long-term anergy of antigen-specific T cells. The immune response to the type II T cell-independent antigen trinintrophenol-conjugated Ficoll, however, was not suppressed. Inhibition of humoral immunity occurred only when anti-4-1BB mAb was given within 1 wk after immunization. Anti-4-1BB inhibition was observed in mice lacking functional CD8(+) T cells, indicating that CD8(+) T cells were not required for the induction of anergy. Analysis of the requirements for the anti-4-1BB-mediated inhibition of humoral immunity revealed that suppression could not be adoptively transferred with T cells from anti-4-1BB-treated mice. Transfer of BALB/c splenic T cells from sheep red blood cell (SRBC)-immunized and anti-4-1BB-treated mice together with normal BALB/c B cells into C.B-17 severe combined immunodeficient mice failed to generate an anti-SRBC response. However, B cells from the SRBC-immunized, anti-4-1BB-treated BALB/c mice, together with normal naive T cells, exhibited a normal humoral immune response against SRBC after transfer, demonstrating that SRBC-specific B cells were left unaffected by anti-4-1BB mAbs.

CpG oligodeoxynucleotides overcome the unresponsiveness of neonatal B cells to stimulation with the thymus-independent stimuli anti-IgM and TNP-Ficoll

Neonates are very vulnerable to pathogenic encapsulated bacteria due to their inability to mount an antibody response to capsular polysaccharides, which are thymus-independent type 2 (TI-2) antigens (Ag). Oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides induced neonatal B cells to proliferate to anti-IgM, a TI-2 stimulus. CpG ODN inhibited the spontaneous and B cell receptor-mediated apoptosis of neonatal B cells and reduced the amount of the pro-apoptotic Bcl-xS, strongly correlated with anti-IgM-induced apoptosis of neonatal B cells. CpG ODN protected neonatal B cells from apoptosis by down-regulation of the Bcl-xS protein. Neonatal B cells underwent polyclonal differentiation upon stimulation with CpG ODN, but unlike in adult B cells, this was not preceded by IL-6 secretion. CpG ODN stimulated neonatal B cells to mount an Ag-specific antibody response to TNP-Ficoll, another TI-2 Ag. Thus CpG ODN could provide a novel approach to induce the immune system in neonates to respond to harmful encapsulated bacteria.

A comparison of the direct and reporter antigen popliteal lymph node assay for the detection of immunomodulation by low molecular weight compounds

The direct popliteal lymph node assay (PLNA) is a predictive test used to detect the immune-stimulating potential of pharmaceuticals and other low molecular weight compounds (LMWCs) with known autoimmunogenic or sensitizing properties. Two limitations in the PLNA are the existence of false negatives and the inability of the assay to provide mechanistic information. Recently the direct PLNA was modified by incorporating reporter antigens (RA), either TNP-Ficoll or TNP-OVA. In the RA-PLNA, immune stimulation is detected by measuring IgM or IgG TNP-specific antibody-forming cells (AFC) using an enzyme-linked immunospot (ELISPOT) assay. The RA-PLNA, when using potent, known autoimmunogenic compounds, may provide greater sensitivity compared to the direct PLNA and might distinguish LMWCs that have intrinsic adjuvant activity from those that create neo-antigens, using TNP-OVA and TNP-Ficoll, respectively. The purpose of this study was to rigorously compare the two assays. Our first objective was to investigate the interlaboratory reproducibility of the RA-PLNA using four autoimmunogenic LMWC models, plus one negative control LMWC. Subsequently, we tested seven LMWCs with known sensitizing properties and compared the results from the direct and modified assay. The test group included LMWCs thought to be mechanistically distinct and similar to compounds typically encountered in preclinical safety assessment. All control and treatment AFC plaques were collected (76 total), pooled, coded to conceal their source, and counted. The interlaboratory reproducibility of the RA-PLNA was demonstrated with the model autoimmunogenic compounds HgCl2, diphenylhydantoin, D-penicillamine, and the negative control compound phenobarbital, by detecting TNP-specific IgM and polyclonal IgG production to both reporter antigens. Additionally, the sensitizing effects of streptozotocin were identified using an IgG2a ELISPOT with both TNP-OVA and TNP-Ficoll. With the extended test group, the sensitizing effects of aniline, a false negative LMWC in the direct PLNA, was not detected in this study when using the direct PLNA. However, there was an increase of IgG1 AFCs using TNP-OVA, when compared to control (508 +/- 113 vs. 12 +/- 4 respectively). Glafenine, diclofenac, and ibuprofen, all associated with drug-induced anaphylaxis in humans, produced significant increases in IgG1 production to TNP-OVA. Of these three LMWCs, only diclofenac, which has been documented to induce neo-antigen formation, was detected with TNP-Ficoll. Hydralazine immunomodulation could be detected only with the direct PLNA although significant increases in IgM were identified with the co-injection of either reporter antigen. Isoniazid and methyldopa consistently produced negative responses in both assays. In summary, this study has demonstrated acceptable interlaboratory reproducibility of the RA-PLNA, using model autoimmunogenic LMWCs. Additionally, it demonstrated that an advantage of the RA-PLNA was that it identified all anaphylactic-associated LMWCs tested, detected the false negative compound aniline, and revealed what is thought to be the mechanism(s) associated with diclofenac-induced immunostimulation.

Cutting edge: CD40 ligand is a limiting factor in the humoral response to T cell-dependent antigens

CD40 ligand (CD40L) plays a crucial role in T cell-dependent B cell responses, but whether its abundance is a limiting factor in their development is unclear. This question was addressed in transgenic mice expressing the murine CD40L gene under the control of the IL-2-promoter (CD40Ltg+). The fraction of activated T cells from the CD40Ltg+ mice with detectable levels of surface CD40L was modestly greater (1.1- to 2-fold) than littermate controls and paralleled an approximately 1.8-fold increase in CD40L mRNA abundance. In response to trinitrophenol (TNP)-keyhole limpet hemocyanin and tetanus/diphtheria vaccine, CD40Ltg+ mice developed higher titers of high-affinity IgG and IgG1 Ab than wild-type mice. In contrast, the Ab response of CD40Ltg+ and control mice was similar in response to the T-independent Ag TNP-Ficoll. These results suggest that a modest increment in expression of CD40L accelerates the development of T-dependent responses, and that CD40L plays a limiting role in the induction of high-affinity Ab and Ab-class switching.

Deficiency in Msh2 affects the efficiency and local sequence specificity of immunoglobulin class-switch recombination: parallels with somatic hypermutation

During maturation of the immune response, IgM+ B cells switch to expression of one of the downstream isotypes (IgG, A or E). This class switching occurs by region-specific recombination within the IgH locus through an unknown mechanism. A lack of switch recombination in mice deficient in components of the DNA-dependent protein kinase (DNA-PK)-Ku complex has pointed to a role for non-homologous end joining. Here we characterize a switching defect in mice lacking a protein involved in DNA mismatch recognition. Mice deficient in Msh2 give diminished IgG (but not IgM) responses following challenge with both T cell-dependent and T cell-independent antigens. This appears to reflect a B cell-intrinsic defect since B cells from Msh2-deficient mice also exhibit impaired switching (but not blasting or proliferation) on in vitro culture with lipopolysaccharide. Furthermore, those switches that do occur in Msh2-deficient B cells reveal a shift in the distribution of recombination sites used: the breakpoints are more likely to occur in consensus motifs. These results, which intriguingly parallel the effects of Msh2 deficiency on hypermutation, suggest a role for Msh2 in the mechanics of class-switch recombination.

Role of different lymphocyte subpopulations in the formation of non-specific immunoglobulins induced by antigen injection

The formation of antibody and non-specific immunoglobulin under the influence of T-dependent (TD) and type 2 T-independent (TI-2) antigens in mice of two congenic strains CBA (Lyb5-, Lyb5+) and CBA/N (Lyb5-) was studied. TD antigens induced in mice of both strains not only the appearance of antibody-forming cells (AFC), but also a great increase in the number of cells producing non-specific immunoglobulins (nIFC). TI-2 antigens induced the AFC and antigen-dependent nIFC formation in CBA mice only. It is concluded that during immune response to TI-2 antigens not only the AFC appearance but the increase in nIFC formation (polyclonal activation) is due mainly to the mature Lyb5+ B cells.

Augmentation of antigen receptor-mediated responses by histamine H1 receptor signaling

Histamine is considered one of the important mediators of immediate hypersensitivity and inflammation, and acts via G protein-coupled receptors. Here, we report that histamine may affect antigen receptor-mediated immune responses of T and B cells via a signal(s) from histamine H1 receptors (H1Rs). Histamine exhibited enhancing effects on the in vitro proliferative responses of anti-CD3epsilon- or anti-IgM-stimulated spleen T and B cells, respectively, at the culture condition that the fetal calf serum was dialyzed before culture and c-kit-positive cells were depleted from the spleen cells. In studies of histamine H1R knockout mice, H1R-deficient T cells had low proliferative responses to anti-CD3epsilon cross-linking or antigen stimulation in vitro. B cells from H1R-deficient mice were also affected, demonstrating low proliferative responses to B cell receptor cross-linking. Antibody production against trinitrophenyl-Ficoll was reduced in H1R-deficient mice. Other aspects of T and B cell function were normal in the H1R knockout mice. H1R-deficient T and B cells showed normal responses upon stimulation with interleukin (IL)-2, IL-4, CD40 ligand, CD40 ligand plus IL-4, and lipopolysaccharide. Collectively, these results imply that the signal generated by histamine through H1R augments antigen receptor-mediated immune responses, suggesting cross-talk between G protein-coupled receptors and antigen receptor-mediated signaling.

IL-12 enhances antibody responses to T-independent polysaccharide vaccines in the absence of T and NK cells

Polysaccharide vaccines to encapsulated bacteria such as Neisseria meningitidis and Streptococcus pneumoniae are weakly immunogenic due to their T-independent (TI) nature. Even when converted to T-dependent forms through conjugation to foreign proteins, polysaccharides induce responses that are deficient in many respects, such as induction of murine IgG2a Ab, the isotype that mediates optimal complement fixation and opsonization. We now show that IL-12 treatment of mice induces significantly increased levels of IgG2a Ab to the model TI-2 Ag, DNP-Ficoll, and to vaccines composed of polysaccharides from pneumococci and meningococci. Use of immunodeficient mice lacking T cells and/or NK cells demonstrated that such cells were not responsible for the observed Ab enhancement. Furthermore, the use of IFN-gamma knockout mice showed that stimulation of TI-2 Ab responses by IL-12 was only partially dependent on IFN-gamma. The ability of IL-12 to dramatically enhance TI Ab responses suggests that IL-12 will be useful as a powerful vaccine adjuvant to induce protective immune responses against encapsulated pathogens.

Neonatal murine B lymphocytes respond to polysaccharide antigens in the presence of IL-1 and IL-6

Unlike adults, neonates are unable to respond to polysaccharide Ags, making them especially vulnerable to pathogenic encapsulated bacteria. Since the Ab response to polysaccharides in adult mice requires certain cytokines, it was hypothesized that neonatal murine B cells may be competent to respond to such Ags, but may fail to do so due to a deficiency of cytokines. Neonatal splenocyte cultures, which were otherwise unresponsive to trinitrophenyl (TNP)-Ficoll, a haptenated polysaccharide Ag, mounted an adult-like Ab response when supplemented with IL-1. However, IL-1 failed to induce such a response to TNP-Ficoll when purified B cells were used instead. Although IL-6 alone did not induce a response in whole spleen cells or purified B cells from neonates, it synergized with IL-1 in inducing purified neonatal B cells to respond to TNP-Ficoll. The avidity of the cytokine-induced neonatal anti-TNP Abs was comparable to that of Abs made by adult splenocyte cultures. One effect of IL-1 may be at the level of clonal expansion, since it induced neonatal B cells to proliferate in response to anti-IgM, which was further enhanced by IL-6. The spontaneous secretion of IL-1 by neonatal splenocytes was below the detection limit, while adult splenocytes secreted 30.8 +/- 5.2 U/ml, which is of the same order of magnitude as what was required to stimulate neonatal B cells to respond to TNP-Ficoll. Thus, the neonatal unresponsiveness to polysaccharide Ags could be due to the inability of a non-B cell population resident in the neonatal spleen to secrete sufficient quantities of IL-1.

Immunological studies on PD-1 deficient mice: implication of PD-1 as a negative regulator for B cell responses

PD-1, an Ig superfamily member, contains an immunoreceptor tyrosine-based inhibitory motif in the cytoplasmic tail. It is expressed in a minor fraction of CD4-CD8- normal thymocytes and induced in peripheral lymphocytes following activation. To assess the possible roles of PD-1 in the immune responses, PD-1-deficient (PD-1-/-) mice were generated by a gene-targeting strategy. PD-1-4- mice developed and grew normally. Although the thymus was apparently normal, PD-1-/- mice showed moderate but consistent splenomegaly, which reflected the increased cellularity of both lymphoid and myeloid cells. The proliferative response of B cells by anti-IgM antibodies, but not of T cells by an anti-CD3 (145-2C11) mAb in vitro, was augmented in PD-1-/- mice as compared with control littermates. PD-1-/- mice showed increased serum levels of IgG2b, IgA and most strikingly IgG3, while those of IgM and IgG1 were comparable with control mice. Furthermore, PD-1-/- mice exhibited significantly augmented IgG3 anti-DNP antibody response to a type 2 T-independent antigen, DNP-Ficoll, with comparable IgM and IgG1 antibody responses with littermate controls. In the peritoneal cavity, the B-1 cell population in PD-1-/- mice exhibited significantly reduced expression of CD5, a negative regulator of B-1 cell activation, despite a marginal increase in the number of B-1 cells. Thus, PD-1 was suggested to be involved in the negative regulation for particular aspects of B cell proliferation and differentiation including class switching.

Assessment of the charge selectivity of glomerular basement membrane using Ficoll sulfate

The extent to which the glomerular basement membrane (GBM) contributes to the charge selectivity of the glomerular capillary wall has been controversial. To reexamine this issue, the size and charge selectivity of filters made from isolated rat GBM were assessed, using polydisperse Ficoll and Ficoll sulfate as test macromolecules. Ficoll sulfate, a novel tracer with spherical shape synthesized for this purpose, exhibited little or no binding to serum albumin, thereby avoiding a major difficulty that has been reported with dextran sulfate. The sieving coefficients of Ficoll sulfate were not different from those of Ficoll at physiological ionic strength, although the values for Ficoll sulfate were depressed at low ionic strength. These results confirm that the GBM possesses fixed negative charges but suggest that its charge density is insufficient to confer significant charge selectivity under physiological conditions, where electrostatic interactions are relatively well screened. The sieving coefficients of Ficoll sulfate and Ficoll were elevated significantly and by similar amounts when bovine serum albumin (BSA) was present in the retentate at 4 g/dl. This could be explained as the combined effect of two nonspecific physical factors, namely, the reduction in filtration velocity due to the osmotic pressure of BSA and the effect on macromolecular partitioning of repulsive solute-solute interactions. The view that BSA does not affect the intrinsic properties of the GBM is supported also by the absence of an effect on the hydraulic permeability of isolated GBM. The sieving coefficient of BSA was roughly half that of Ficoll or Ficoll sulfate of similar Stokes-Einstein radius. Given the finding of negligible charge selectivity, this difference may be attributed to the nonspherical shape of albumin. The results suggest that, to the extent that isolated GBM is similar to GBM in vivo, the charge selectivity of the glomerular capillary wall must be due to the endothelial and/or epithelial cell layers.

Selective immunomodulation by the autoimmunity-inducing xenobiotics streptozotocin and HgCl2

Exposure to certain drugs and environmental chemicals can provoke the onset of autoimmune disease in susceptible individuals by releasing (self) epitopes for which tolerance has not been established, while simultaneously providing the necessary adjuvant activity. The resulting response type is influenced by the genotype of exposed individuals and relates to susceptibility to the adverse immune effects of the chemicals. Here, we assessed the modulatory role of the chemical compounds themselves. A single injection of streptozotocin (STZ) increased the number of CD8+ cells, macrophages, apoptotic cells, and IFN-gamma-producing T helper and T cytotoxic cells, whereas the number of CD4+ cells and B cells was reduced in the draining lymph node. Coinjection with the reporter antigen TNP-OVA resulted in primary and secondary production of TNP-specific antibodies that were predominantly of IgG2a and IgG2b isotype, whereas STZ did not enhance priming for delayed-type hypersensitivity (DTH) responses to TNP-OVA. Injection of HgCl2 on the other hand, reduced the number of IFN-gamma-producing cells, induced accumulation of B cells and CD4+ and CD8+ T cells, enhanced IgG1 and IgE production to TNP-OVA, and primed for secondary IgG1 and IgE production as well as for DTH reactions. Together these results indicate that a single injection of STZ stimulates type-1 responses, whereas HgCl2 enhanced mixed type-1 and -2 responses in BALB/c mice. These response types match the (auto)immune effects elicited to unknown (auto)antigens following multiple injections of these chemicals.

Antibodies with idiotypic and anti-idiotypic reactivity (epibodies) in conventional immune responses to dinitrophenylated carriers

A number of monoclonal antibodies were derived from the spleen cells of dinitropheryl (DNP)-immunized mice. Both T-dependent and T-independent carriers were used, and the intensity and length of immunization were varied. It was found that some of the antibodies had only idiotypic (Ab1) reactivity, while others had both idiotypic (Ab1) and anti-idiotypic (Ab2) reactivity. Among the latter antibodies some molecules reacted specifically with DNP and with the combining site of anti-DNP antibodies (epibodies), while others bound DNP and anti-DNP Abs as well as a variety of unrelated antigens (polyreactive antibodies). The proportion of the three types of antibodies (antigen-specific, epibodies and polyreactive antibodies) varied with the nature of the carrier, the intensity of the immunization, and the length of the immunization process. Further characterization of the epibodies, which were predominant in the secondary response to DNP-keyhole limpet haemocyanin (KLH), showed that both Ab1 and Ab2 reactivities were inhibited by both soluble ligands (DNP and anti-DNP), indicating that the specific combining site of the monoclonal antibodies (mAbs) (and/or of the rabbit anti-DNP antibody in the case of Ab2) was involved in both activities. Both Ab1 and Ab2 reactivities were removed by absorption of the mAbs with either immobilized DNP or immobilized rabbit anti-DNP. The mAbs were capable of binding themselves as well as to other mAbs with the same characteristics. The affinity constants of several mAbs for both the DNP and anti-DNP ligands were determined.

Beta 2-microglobulin-deficient mice are protected from hypergammaglobulinemia and have defective antibody responses because of increased IgG catabolism

The goal of this study was to determine whether class I proteins play an important role in the regulation of Ig and to elucidate the mechanism(s) involved. We analyzed the phenotype imposed by a null allele of beta 2-microglobulin (beta 2m). Serum Ig levels of several mouse strains showed a beta 2m dependence that was most evident in mice genetically predisposed to develop chronic systemic lupus erythematosus, was preferential to IgG isotypes, and was greatly exaggerated in aging mice that normally develop hypergammaglobulinemia. Beta 2m-deficient mice, regardless of genetic background, also displayed a substantial reduction of specific Ab in response to a prototypic T cell-dependent Ag and a prototypic T cell-independent 2 Ag. This reduction could be accounted for by a selective diminution of Abs of the IgG class. Therefore, class I proteins play a considerable role in the regulation of Ig. The beta 2m dependence could not be explained by class I-dependent immunoregulatory cells (CD8+ cells, NK1.1+ T cells, or conventional NK+ cells) or by the transfer of maternal IgG into the prenatal/neonatal mouse made possible by the beta 2m-dependent Fc receptor (FcRn). However, a beta 2m-dependent increase in the half-lives of IgG, presumably conferred by lifelong FcRn expression, was observed in all mice regardless of genetic background and age. We conclude that FcRn-mediated protection of IgG from catabolism is a generic mechanism that best explains the lifelong beta 2m dependence of Ig in both normal and pathologic situations.

The effect of linomide, an immunoregulator in experimental autoimmune diseases, on humoral antibody responses in mice

Linomide (quinoline-3-carboxamide), a well tolerated, orally administered compound was recently shown to be effective in the prevention and treatment of several autoimmune diseases in experimental animal models. We have investigated its effect on specific humoral immune responses directed to T-cell-dependent soluble or particulate antigens and to a T cell-independent antigen in several mouse strains. Linomide administered after antigen priming did not affect primary and secondary antibody responses directed to T-cell particulate antigens (SRBC) or soluble antigens given with or without complete Freund's Adjuvant (CFA). Linomide treatment given prior to antigen priming did not affect the antibody response to a soluble antigen (TNP-KLH) given with an adjuvant. In contrast, dose-dependent down regulation of primary antibody responses was observed when T cell-dependent (BSA-dextran) or T-cell-independent (TNP-Ficoll) antigens were administered in an immunogenic form without adjuvant after starting Linomide treatment. The primary anti-SRBC antibody response was also suppressed by high dose Linomide given prior to immunization although normal secondary responses were retained. It is worth noting that no immunosuppressive effects on antibody responses were found at low dose ranges which effectively reversed T cell dependent autoimmune manifestation.

Translational diffusion of macromolecule-sized solutes in cytoplasm and nucleus

Fluorescence recovery after photobleaching (FRAP) was used to quantify the translational diffusion of microinjected FITC-dextrans and Ficolls in the cytoplasm and nucleus of MDCK epithelial cells and Swiss 3T3 fibroblasts. Absolute diffusion coefficients (D) were measured using a microsecond-resolution FRAP apparatus and solution standards. In aqueous media (viscosity 1 cP), D for the FITC-dextrans decreased from 75 to 8.4 x 10(-7) cm2/s with increasing dextran size (4-2,000 kD). D in cytoplasm relative to that in water (D/Do) was 0.26 +/- 0.01 (MDCK) and 0.27 +/- 0.01 (fibroblasts), and independent of FITC-dextran and Ficoll size (gyration radii [RG] 40-300 A). The fraction of mobile FITC-dextran molecules (fmob), determined by the extent of fluorescence recovery after spot photobleaching, was >>0.75 for RG << 200 A, but decreased to <<0.5 for RG >> 300 A. The independence of D/Do on FITC-dextran and Ficoll size does not support the concept of solute "sieving" (size-dependent diffusion) in cytoplasm. Photobleaching measurements using different spot diameters (1.5-4 micron) gave similar D/Do, indicating that microcompartments, if present, are of submicron size. Measurements of D/Do and fmob in concentrated dextran solutions, as well as in swollen and shrunken cells, suggested that the low fmob for very large macromolecules might be related to restrictions imposed by immobile obstacles (such as microcompartments) or to anomalous diffusion (such as percolation). In nucleus, D/Do was 0.25 +/- 0.02 (MDCK) and 0.27 +/- 0.03 (fibroblasts), and independent of solute size (RG 40-300 A). Our results indicate relatively free and rapid diffusion of macromolecule-sized solutes up to approximately 500 kD in cytoplasm and nucleus.