Immunology. Long live the mature B cell--a baffling mystery resolved

What determines whether transitional B cells newly emerged from the bone marrow will differentiate further to become mature, long-lived, circulating B lymphocytes? In a Perspective, Waldschmidt and Noelle discuss new findings showing that the TNF family ligand BAFF and its receptor BAFF-R are crucial for selecting transitional B cells into the mature B cell pool (Thompson et al., Schiemann et al.).

TH1 cytokine response of CD57+ T-cell subsets in healthy controls and patients with alcoholic liver disease

Patients with chronic inflammatory diseases, including Crohn's disease and rheumatoid arthritis, as well as those with certain viral infections, and patients who are transplant recipients or who have certain hematologic malignancies have been observed to have CD57+ T cell expansion in both CD4+ and CD8+ subsets. We have reported previously that alcoholic patients also have CD57+ T cell expansion. Because many alcoholics become seriously deficient in cell-mediated immunity, it is of interest to determine whether the expanded CD57+ subsets can respond to stimulation with normal T helper cell subtype 1 (TH1) cytokine production. We report evaluation of the CD57 T-cell subsets of patients with alcoholic liver disease (ALD) with the use of cytoplasmic staining after stimulation through the T-cell receptor (TCR). The CD57+ subsets of the T cells of both healthy individuals and patients with ALD express significantly higher amounts of cytoplasmic tumor necrosis factor-alpha (TNF-) and interferon-gamma (IFN-) after 6 h of stimulation than do the CD57- subsets. This increased production can persist up to 46 h of continuous stimulation. Under these assay conditions, very little cytoplasmic interleukin (IL)-4 is observed in the T cells of either healthy control subjects or patients with ALD. Measurement of cytokine secretion by sort-purified CD57 T-cell subsets with the use of enzyme-linked immunosorbent assay (ELISA) shows that the CD57+ T-cell subset produces 18- to 30-fold more TNF- and IFN-, respectively, than does the CD57- subset in the first 12 h of stimulation. This response requires only stimulation through the TCR for the CD57+ subset, whereas significant secretion by the CD57- subset requires added IL-2 or anti-CD28 antibody. These results are consistent with the concept of the CD57+ T-cell subset as a differentiated effector cell and demonstrate that patients with ALD who are not drinking at the time of evaluation have normal or increased immediate TH1 T-cell responses.

Immunotoxicity of explosives-contaminated soil before and after bioremediation

Soils from the Yorktown Naval Base contaminated with trinitrotoluene (TNT) and other explosives were used to prepare eluates before and after bioremediation using microbial growth amendments in the presence (P1 eluates) or absence (P2 eluates) of exogenous white rot fungus. Effectiveness of bioremediation was examined by several immunotoxicity assays-viability/growth of lymphocytes, cytokine production, and expression of the interleukin-2 (IL-2) receptor-using human peripheral blood mononuclear cells exposed to the eluates. Although TNT concentrations decreased in both P1 and P2 eluates relative to untreated baseline soil (BL) eluates, a recovery in lymphocyte growth/viability and IL-2 secretion was seen with P2 but not P1 eluates relative to BL eluates. IL-2 receptor levels were higher in cells exposed to BL and P2 eluates than when exposed to P1 eluates. Interferon-gamma, tumor necrosis factor-beta, and IL-10 levels were highest in BL and P2 eluates and lowest in P1 eluates. Taken together, these results suggest that treatment of the soil with microbial growth amendments in the absence but not the presence of exogenous white rot fungi lead to partial bioremediation as assessed by lymphocyte functions.

Delineation among eight major hematopoietic subsets in murine bone marrow using a two-color flow cytometric technique

BACKGROUND

Many methods have been developed specifically for identifying hematopoietic progenitor cells in murine bone marrow, but few methods allow rapid identification of multiple bone marrow populations. We describe a new, simple method for identifying simultaneously eight populations in murine bone marrow with two-color flow cytometry and phenotypically define these populations.

METHODS

Bone marrow was stained with anti-Ly-6C and anti-B220 (CD45R) in one fluorochrome and wheat germ agglutinin (WGA) in another fluorochrome. The eight populations identified in this way were defined further primarily by four-color flow cytometry.

RESULTS

Six of the eight populations were characterized phenotypically as containing erythroid, granulocytic, mast, early B, mature B, and stem cell populations. Two additional populations with phenotypic characteristics of partially differentiated precursor cells also were identified. One population was Ly-6C/B220+ and WGA-. It also expressed markers associated with early B, T, and/or dendritic cell differentiation. The second population was Ly-6C(hi)WGA(hi)Mac-1+ and was negative for numerous other lineage-specific and precursor markers. Its morphology suggested monocytic differentiative potential.

CONCLUSIONS

A two-color flow cytometric assay profiles six bone marrow populations with identifiable phenotypes and two additional unique, putative hematopoietic precursor populations.

Murine B1 B cells require IL-5 for optimal T cell-dependent activation

T helper cell-driven activation of murine B cells has been shown to depend upon CD40-CD40 ligand (CD40L) interactions and a defined set of cytokines. These observations are primarily based on the use of conventional B cells obtained from the spleen. Therefore, it is presently unclear whether all mature B cell subsets found in the mouse have an equal dependence upon CD40-CD40L interactions and use the same T cell-derived cytokines. The present study tested the response of splenic follicular and marginal zone as well as peritoneal B2 and B1 B cells to Th cell stimulation. Splenic and peritoneal B cell subsets were sort purified based on CD23 expression, and cultured with rCD40L and cytokines or Th2 cells. The results demonstrate that follicular, marginal zone, and peritoneal B2 B cells require CD40-CD40L interactions and preferentially use IL-4 for optimal proliferation, differentiation, and isotype switching. In contrast, peritoneal B1 B cells use IL-5 in conjunction with CD40-CD40L interactions for maximal Th cell-dependent responses. Furthermore, B1 B cells are capable of proliferating, differentiating, and isotype switching in the absence of CD40-CD40L interactions. B1 B cells are able to respond to Th2 clones in the presence of anti-CD40L mAb as well as to Th2 clones derived from CD40L(-/-) mice. The CD40-CD40L-independent response of B1 B cells is attributable to the presence of both IL-4 and IL-5, and may explain the residual Ab response to T cell-dependent Ags in CD40L- or CD40-deficient mice, and in X-linked hyper-IgM (X-HIM) patients.

The immune response modifiers imiquimod and R-848 are potent activators of B lymphocytes

Imiquimod and R-848 are members of a family of immune response modifiers that stimulate cytokine production in monocyte/macrophages and dendritic cell cultures. This study evaluated the effects of the imidazoquinolines, imiquimod and R-848, on B lymphocyte activation. Both agents induced proliferation of murine T-cell-depleted and highly purified splenic B cell preparations as well as purified human B cells. Resting and activated B cells responded to these agents, with activated cells responding more efficiently. B cells from the LPS-hyporesponsive C3H/HeJ mice and guanosine-hyporesponsive SJL mice proliferated in response to imiquimod and R-848, indicating a different mechanism of action than lipopolysaccharide and guanine nucleosides. B cells were also stimulated by imiquimod and R-848 to produce increased immunoglobulin levels. Increased expression of a number of B cell activation markers were seen following imiquimod or R-848 stimulation. Finally, R-848 was shown to act as a vaccine adjuvant enhancing OVA-specific IgG2a levels while suppressing total IgE. These results indicate that R-848 and imiquimod are potent activators of B lymphocytes and are capable of augmenting antigen-specific immunoglobulin production.

Identification of murine germinal center B cell subsets defined by the expression of surface isotypes and differentiation antigens

Germinal centers (GCs) are inducible lymphoid microenvironments that support the generation of memory B cells, affinity maturation, and isotype switching. Previously, phenotypic transitions following in vivo B cell activation have been exploited to discriminate GC from non-GC B cells in the mouse and to delineate as many as seven distinct human peripheral B cell subsets. To better understand the differentiative processes occurring within murine GCs, we sought to identify subpopulations of GC B cells corresponding to discrete stages of GC B cell ontogeny. We performed multiparameter flow-cytometric analyses of GC B cells at consecutive time points following immunization of BALB/c mice with SRBC. We resolved the murine GC compartment into subsets based on the differential expression of activation markers, surface Ig isotypes, and differentiation Ags. Class-switched and nonswitched GC B cells emerged contemporaneously, and their relative frequencies remained nearly constant throughout the GC reaction, perhaps reflecting the establishment of a steady state. A significant percentage of the nonswitched B cells with a GC phenotype exhibited surface markers associated with naive B cells, including CD23, surface IgD, and high levels of CD38 consistent with either prolonged recruitment into the GC reaction or protracted expression of these markers during differentiation within the GC. Expression of the activation marker BLA-1 was dynamic over time, with all GC B cells being positive early after immunization, followed by progressive loss as the GC reaction matured into the second and third week. Implications of these results concerning GC evolution are discussed.

CpG oligodeoxynucleotides do not require TH1 cytokines to prevent eosinophilic airway inflammation in a murine model of asthma

BACKGROUND

Oligodeoxynucleotides (ODNs) containing the dinucleotide CpG in a specific sequence context (CpG-ODNs) have the ability to prevent the development of eosinophilic airway inflammation and bronchial hyperreactivity in a murine model of asthma. We have previously demonstrated that CpG-ODNs stimulate expression of the T(H1)-inducing cytokines IFN-gamma and IL-12 in a murine model of asthma and that this stimulation is associated with the protection against asthmatic inflammation.

OBJECTIVE

The purpose of this study was to examine whether the protection conferred by CpG-ODNs in a schistosome egg-egg antigen murine model of asthma is dependent on the induction of IFN-gamma, IL-12, or both.

METHODS

C57BL/6 mice were sensitized to schistosome eggs in the presence or absence of CpG-ODNs or control ODNs and then stimulated with soluble egg antigen in the airway. The protection offered by CpG-ODNs in these mice was compared with the protection induced by CpG-ODNs in IL-12 and IFN-gamma knockout mice and in mice treated with anticytokine blocking antibodies. Double-knockout mice (IL-12/IFN-gamma) were also generated and used in these studies. Determinations included airway eosinophilic inflammation and bronchial hyperreactivity to inhaled methacholine.

RESULTS

We found that CpG-ODNs confer protection against both airway eosinophilia and bronchial hyperreactivity in the absence of IFN-gamma or IL-12 or in the presence of both cytokines together. However, in the absence of either IL-12 or IFN-gamma, mice require 10 times as much CpG-ODNs to be protected against the induction of airway eosinophilia. The T(H2) cytokines IL-4 and IL-5 were reduced in all of the CpG-treated mice, although less in the absence of IL-12 and IFN-gamma.

CONCLUSION

These data indicate that CpG-ODNs prevent the generation of T(H2)-like immune responses by multiple mechanisms, which involve, but do not require, IL-12 and IFN-gamma. A direct suppressive effect of CpG-ODNs on T(H2) responses is suggested by their reduction in IFN-gamma and IL-12 knockout mice.

SLP-76 expression is restricted to hemopoietic cells of monocyte, granulocyte, and T lymphocyte lineage and is regulated during T cell maturation and activation

The leukocyte-specific adapter protein SLP-76 is known to augment the transcriptional activity of nuclear factor of activated T cells and AP-1 following TCR ligation. A role for SLP-76 in additional receptor-mediated signaling events is less clear. To define the pattern of SLP-76 expression during murine hemopoiesis, we stained cells isolated from various tissues with a combination of surface markers followed by intracellular staining with a fluorochrome-labeled SLP-76-specific Ab. In the bone marrow, SLP-76 expression is largely restricted to cells of granulocyte and monocyte lineage. Heterogeneous SLP-76 expression is first detected in the CD44+ CD25- subset within the CD3- CD4- CD8- thymocyte population. Interestingly, SLP-76 expression increases as thymocyte maturation progresses within the CD4- CD8- compartment but decreases as cells mature to a CD4+ CD8+ phenotype. SLP-76 expression is then up-regulated following selection and concomitant with maturation to a CD4+ or CD8+ phenotype. In the periphery, SLP-76 is expressed in T lymphocytes with no detectable expression in the B cell compartment. Exposure to the superantigen staphylococcal enterotoxin B augments SLP-76 expression in the reactive T cell subset. Furthermore, in vitro stimulation with TCR-specific Abs augments the existing levels of SLP-76. These data reveal that SLP-76 expression is coordinately regulated with surface expression of a pre-TCR or mature TCR complex during thymocyte development and that TCR ligation elicits signals that result in increased expression of SLP-76.

Modulation of airway inflammation by CpG oligodeoxynucleotides in a murine model of asthma

Asthma has been increasing in industrialized countries. Evidence suggests that asthma is caused by a Th2 immune response to inhaled environmental Ags and that childhood infections protect against this. We have shown that bacterial DNA contains motifs, centered on unmethylated CpG dinucleotides, which induce Th1-type responses. We hypothesized that the Th1 effect of these CpG motifs may oppose the Th2 type allergic response and suggest that this may account for the protective effect of childhood infection against asthma. We examined the effects of CpG-motif oligodeoxynucleotides (CpG ODN) in a murine model of asthma. Airway eosinophilia, Th2 cytokine induction, IgE production, and bronchial hyperreactivity were prevented by coadministration of CpG ODN with the Ag. Significantly, in a previously sensitized mouse, CpG ODN can prevent allergen-induced airway inflammation. These studies suggest that exposure to CpG DNA may protect against asthma.

CpG DNA is a potent enhancer of specific immunity in mice immunized with recombinant hepatitis B surface antigen

Unmethylated CpG dinucleotides in bacterial DNA or synthetic oligodeoxynucleotides (ODN) cause B cell proliferation and Ig secretion, monocyte cytokine secretion, and activation of NK cell lytic activity and IFN-gamma secretion in vivo and in vitro. The potent immune activation by CpG ODN suggests possible utility for enhancing immune responses to vaccines. Mice immunized with recombinant hepatitis B virus surface Ag and a CpG ODN as an immune enhancer have titers of Abs against HBsAg (anti-HBs) that are five times higher than those of mice immunized with HBsAg and the standard adjuvant, aluminum hydroxide (alum). Ab titers in mice immunized with HBsAg and both CpG ODN plus alum were 35 times higher than the titers in mice immunized with alum alone, indicating a strong synergistic interaction between the CpG ODN and alum. ODN without CpG motifs had little or no immune-enhancing activity at the doses used herein. Alum induces a Th2 humoral response (mostly IgG1) and no CTL. In contrast, CpG ODN gives a strong Thl response with predominantly IgG2a Abs and CTL, even when mixed with alum. In vitro studies to determine possible mechanisms of CpG immune-enhancing effects show that CpG ODN induce expression of costimulatory molecules on Ag-presenting cells and drive B cell isotype switching in the appropriate cytokine milieu. These studies demonstrate that CpG ODN are promising new immune enhancers for vaccination applications.

Mouse complement receptors type 1 (CR1;CD35) and type 2 (CR2;CD21): expression on normal B cell subpopulations and decreased levels during the development of autoimmunity in MRL/lpr mice

Human complement receptors type 1 (hCR1;CD35) and type 2 (hCR2;CD21) are expressed on B lymphocytes at specific stages during differentiation and activation. These receptors play critical roles in the immune response to T-dependent Ags in addition to germinal center formation. Expression of both hCR2 and hCR1 is decreased on B lymphocytes of patients with systemic lupus erythematosus (SLE). We have studied the expression of mouse CR2 and CR1 on normal populations of mouse B lymphocytes in BALB/c mice. Our results demonstrate that expression of these receptors in the normal state closely parallels that of hCR2. During bone marrow development, expression is first detected on low B220/high IgM cells, demonstrating that complement receptors appear after central tolerance mechanisms are completed. In the splenic microenvironment the highest levels of receptor expression are found on marginal zone B lymphocytes. Mouse CR2 and CR1 are also found on peritoneal B1a and B1b cells in addition to IgA+ Peyer's patch B cells. Activation of splenic B cells under Th2 conditions results in a marked decrease in receptor expression. To determine whether the patterns of receptor expression also parallel those found in human disease, we studied the MRL lpr/lpr (MRL/lpr) model of SLE. Interestingly, we found an early decrease in complement receptor expression that is progressive and first detectable before major clinical manifestations of nephritis. We hypothesize that the early decrease in complement receptor expression such as that demonstrated by MRL/lpr mice plays an important role in the pathogenesis of murine and perhaps human SLE.

Mouse complement receptors type 1 (CR1;CD35) and type 2 (CR2;CD21): expression on normal B cell subpopulations and decreased levels during the development of autoimmunity in MRL/lpr mice

Human complement receptors type 1 (hCR1;CD35) and type 2 (hCR2;CD21) are expressed on B lymphocytes at specific stages during differentiation and activation. These receptors play critical roles in the immune response to T-dependent Ags in addition to germinal center formation. Expression of both hCR2 and hCR1 is decreased on B lymphocytes of patients with systemic lupus erythematosus (SLE). We have studied the expression of mouse CR2 and CR1 on normal populations of mouse B lymphocytes in BALB/c mice. Our results demonstrate that expression of these receptors in the normal state closely parallels that of hCR2. During bone marrow development, expression is first detected on low B220/high IgM cells, demonstrating that complement receptors appear after central tolerance mechanisms are completed. In the splenic microenvironment the highest levels of receptor expression are found on marginal zone B lymphocytes. Mouse CR2 and CR1 are also found on peritoneal B1a and B1b cells in addition to IgA+ Peyer's patch B cells. Activation of splenic B cells under Th2 conditions results in a marked decrease in receptor expression. To determine whether the patterns of receptor expression also parallel those found in human disease, we studied the MRL lpr/lpr (MRL/lpr) model of SLE. Interestingly, we found an early decrease in complement receptor expression that is progressive and first detectable before major clinical manifestations of nephritis. We hypothesize that the early decrease in complement receptor expression such as that demonstrated by MRL/lpr mice plays an important role in the pathogenesis of murine and perhaps human SLE.

Distribution of Ly-6C on lymphocyte subsets: I. Influence of allotype on T lymphocyte expression

The expression patterns of the Ly-6C Ag were examined on splenic and thymic lymphocyte subsets of Ly-6.1 and Ly-6.2 strains of mice using the rat mAb 15.1. Ly-6C is expressed on subsets of CD4+ and CD8+ splenocytes, and a portion of NK cells. Within the splenic and lymph node CD4+ T cell compartment, Ly-6C expression is restricted to Ly-6.2 strains of mice, and is present on a subset of naive cells. Ly-6C is expressed on the majority of peripheral CD8+ T cells in both Ly-6.1 and Ly-6.2 strains, and is found primarily on the Ag-experienced subset. In the thymus, Ly-6C is present on subpopulations of CD4- CD8+, CD4- CD8-, and CD4+ CD8- cells. Ly-6C+ CD4- CD8+ thymocytes show a mature phenotype, while Ly-6C+ CD4- CD8- and Ly-6C+ CD4+ CD8- thymocytes appear to be part of the recently described NK1.1+ alphabeta TCR+ population. On account of the marked differences in Ly-6C expression on peripheral CD4+ T cells from Ly-6.1 and Ly-6.2 strains of mice, additional experiments were undertaken to assess Ly-6C expression in parental and Ly-6.1 x Ly-6.2 F1 mice. Neither phenotype dominated in the F1 offspring, with frequencies of Ly-6C+ CD4+ splenocytes falling in the intermediate range. Further experiments compared the staining patterns of the rat anti-pan Ly-6C (Ly-6.1 and Ly-6.2) Ab with a mouse anti-Ly-6.2 allotype specific Ab, with emphasis on both Ly-6.2 and Ly-6.1 x Ly-6.2 F1 mice. The results demonstrate the presence of lymphocytes that express the pan form of Ly-6C but not the form recognized by the alloantibody. This latter finding suggests the presence of more than one form of the Ly-6C Ag.

Estrogen inhibits fetal thymocyte development in vitro

PROBLEM

Transient involution of the maternal thymus in mice is known to occur during pregnancy. We have previously reported that the hormone responsible for this involution is estrogen. Interestingly, although estrogen crosses the placenta, fetal thymus gland enlarges with advancing gestational age. It is not known if fetal thymocytes are resistant to estrogen or if there are other factors that prevent estrogen from exerting an effect on the development of fetal thymocytes. Therefore we studied the effect of estrogen on isolated fetal thymic glands in vitro. METHOD OR STUDY: Pregnant Balb/c mice were sacrificed at 15 days gestation and fetal thymic lobes were obtained from all fetuses. The glands were cultured in vitro using either control medium or medium to which estrogen was added in two concentrations of 0.5 mg/ 100 ml and 1.0 mg/100 ml. After 12 days of organ culture, total thymocyte counts and phenotypic analysis by three color flow cytometry were performed by using monoclonal antibodies to surface markers of T cells subsets.

RESULTS

Estrogen treatment caused a marked suppression of the total number of fetal thymocytes. All CD4 and CD8 defined T cell subsets were reduced with a disproportionate loss of CD4+ single positive (SP), CD8+ SP: CD4+CD8+ double positive (DP) cells. The early thymocyte developmental stages, based on CD44 and CD25 expression, revealed the CD4-CD8-CD3- triple negative compartment (TN) to be composed of almost entirely the earliest population (CD44+CD25-) with the remaining maturational stages depleted.

CONCLUSIONS

This study demonstrates that fetal thymus removed from the intact fetus is susceptible to the inhibitory effects of estrogen. Since the fetal thymus enlarges with advanced gestational age, it is clear that the intact fetus invokes a regulatory mechanism which neutralizes the anti-lymphopoietic action of estrogen observed in the adult female.

Fas-mediated apoptosis in human prostatic carcinoma cell lines

Of six prostatic carcinoma cell lines examined (ALVA31, DU145, JCA1, LNCaP, ND1, and PC3) by flow cytometric analysis, all were found to be positive for Fas antigen. Furthermore, of the prostate tissue specimens studied (six cases), all revealed Fas expression in benign and malignant epithelial cells. The agonistic anti-Fas monoclonal antibody (IPO-4) induced apoptosis in only two of six cell lines investigated, PC3 and ALVA31. PCR analysis indicated that all cell lines expressed normal transmembrane and death domains of Fas antigen. Using Western blot analysis, we found abundant expression of p53 in the cytoplasm of two Fas-resistant cell lines, DU145 and ND1, and did not find p53 in two Fas-sensitive cell lines, PC3 and ALVA31. Western blot and PCR analysis did not show consistent differences between cell lines examined in the expression of Bcl-2, Bcl-X(L), Bcl-X(S), and Bak. In contrast, Bax protein was not detected in two Fas-resistant cell lines, DU145 and ND1. We also showed that three Fas-resistant cell lines, DU145, ND1, and JCA1, expressed CD40, whereas the two Fas-sensitive cell lines, PC3 and ALVA31, were CD40 negative. Fas-sensitive cell lines were transfected with the cDNA encoding CD40, and the CD40-positive transfectant became more resistant to growth inhibition mediated by treatment with TNF-alpha and anti-Fas monoclonal antibody. Treatment with cycloheximide converted the phenotype of resistant cell lines from Fas resistant to Fas sensitive. Moreover, anti-Fas treatment of both resistant and sensitive cell lines induced rapid tyrosine phosphorylation or dephosphorylation of multiple proteins. These results suggest that the apoptotic machinery involved in DNA fragmentation is already in place in Fas-resistant cell lines, and thus, Fas-mediated apoptosis could be a target for therapeutic intervention.

Distribution of Ly-6C on lymphocyte subsets: I. Influence of allotype on T lymphocyte expression

The expression patterns of the Ly-6C Ag were examined on splenic and thymic lymphocyte subsets of Ly-6.1 and Ly-6.2 strains of mice using the rat mAb 15.1. Ly-6C is expressed on subsets of CD4+ and CD8+ splenocytes, and a portion of NK cells. Within the splenic and lymph node CD4+ T cell compartment, Ly-6C expression is restricted to Ly-6.2 strains of mice, and is present on a subset of naive cells. Ly-6C is expressed on the majority of peripheral CD8+ T cells in both Ly-6.1 and Ly-6.2 strains, and is found primarily on the Ag-experienced subset. In the thymus, Ly-6C is present on subpopulations of CD4- CD8+, CD4- CD8-, and CD4+ CD8- cells. Ly-6C+ CD4- CD8+ thymocytes show a mature phenotype, while Ly-6C+ CD4- CD8- and Ly-6C+ CD4+ CD8- thymocytes appear to be part of the recently described NK1.1+ alphabeta TCR+ population. On account of the marked differences in Ly-6C expression on peripheral CD4+ T cells from Ly-6.1 and Ly-6.2 strains of mice, additional experiments were undertaken to assess Ly-6C expression in parental and Ly-6.1 x Ly-6.2 F1 mice. Neither phenotype dominated in the F1 offspring, with frequencies of Ly-6C+ CD4+ splenocytes falling in the intermediate range. Further experiments compared the staining patterns of the rat anti-pan Ly-6C (Ly-6.1 and Ly-6.2) Ab with a mouse anti-Ly-6.2 allotype specific Ab, with emphasis on both Ly-6.2 and Ly-6.1 x Ly-6.2 F1 mice. The results demonstrate the presence of lymphocytes that express the pan form of Ly-6C but not the form recognized by the alloantibody. This latter finding suggests the presence of more than one form of the Ly-6C Ag.

Estrogen blocks early T cell development in the thymus

PROBLEM

Pregnancy and estrogen are known to suppress B lymphopoiesis as well as lead to thymic involution in the mouse. Additionally, estrogen deficiency by oophorectomy reportedly causes a selective increase in the B220+ B cells in the murine bone marrow. The purpose of this study was to determine if estrogens played a regulatory role in T cell development.

METHODS

The first experimental group consisted of 5-6-week-old Balb/c mice that received subcutaneous pellets of placebo, estriol, estradiol, or progesterone. The thymus glands were examined 2-4 weeks after treatment. The second group consisted of 6-week-old Balb/c mice who underwent either bilateral oophorectomy or a sham procedure. Two weeks after the surgery, extensive phenotypic characterization of the thymus and spleen cells was performed by flow cytometry using monoclonal antibodies to surface markers of T cell subsets.

RESULTS

Estrogen treatment causes a dramatic reduction of thymic size and cellularity. All defined T cell subsets of CD4 and CD8 were reduced, with a disproportionate loss of CD4+CD8+ double positive cells. Examination of the triple negative (CD3-CD4-CD8-) subset revealed a striking loss of TN developmental progression of the early precursor cells. Based on the expression of CD44 (pgp-1) and CD25 (IL-2R alpha) markers, the TN thymic compartment was composed almost entirely of the earliest population (CD44+, CD25-), with the remaining maturational stages (CD44+, CD25+; CD44-, CD25+; CD44-, CD25-) depleted. In contrast, all T cell developmental stages in the thymus were found to be in normal proportions in the oophorectomized mice, with no differences in the splenic T and B cell subsets.

CONCLUSIONS

The study demonstrates that estrogen but not progesterone blocks T cell development in the thymus. However, contrary to our expectation, estrogen deprivation by oophorectomy does not enhance T cell development.

Differential expression of CD22 (Lyb8) on murine B cells

Previous studies have established the distribution, biochemistry and functional attributes of human CD22, a B cell-restricted glycoprotein. Recently, molecular cloning of the murine CD22 equivalent revealed this molecule to be the same as the previously described Lyb8 alloantigen. Using the anti-Lyb8 mAb Cy34.1.2, the present report documents the expression patterns of CD22 within the murine B cell compartment. The results demonstrate that in the bone marrow, murine CD22 is absent on the surface of pro-B cells, pre-B cells and newly emerging IgM+ B cells. CD22 is present at a low density on immature IgMhi B cells and fully expressed on mature recirculating B cells. In the periphery, murine CD22 is expressed at mature levels on all B cell subsets including follicular, marginal zone, B1 and switched B cells. Further studies showed CD22 to be retained on activated murine B cells for extended periods. Finally, in combination with CD23 and heat stable antigen, CD22 can be used to delineate the immature splenic B cells, and distinguish them from follicular and marginal zone cells. Together, the results demonstrate murine CD22 to be a useful pan marker for all mature B cell subsets.

Effect of pregnancy on thymic T cell development

PROBLEM

The thymus gland decreases in size during pregnancy. The significance of this alteration is not known.

METHOD

In this report, we examined thymic function by evaluating the development of T lymphocytes in the thymus of pregnant Balb/c mice at 15 and 20 days gestation using multi-color flow cytometry. Comparative analysis was made with non-pregnant mice, post-partum lactating mice, and postpartum non-lactating mice.

RESULTS

Progressive reduction of thymic size and cellularity during pregnancy was observed. All of the CD4 and CD8 defined subsets were reduced, with a disproportionate loss of CD4+, CD8+ double positive cells. Examination of the CD4-, CD8- double negative compartment revealed a predominance of TCR alpha, beta+ double negative cells, and a striking loss of precursor cells. The CD3-, CD4-, CD8- triple negative thymic subset was composed almost entirely of the earliest population (CD44+, CD25-), with the remaining maturational stages (CD44+, CD25+; CD44-, CD25+; and CD44-, CD25-) depleted. At 2 weeks postpartum, the subset ratios normalized, and the total cell count showed recovery.

CONCLUSION

T cell development is blocked at the precursor level during the mouse pregnancy. These effects are transient, and gradual recovery is observed in the postpartum period.

Loss of the CD5+ and CD45RAhi B cell subsets in alcoholics

Chronic alcoholics are frequently immunodeficient, have polyclonal hypergammaglobulinaemia, and often have autoantibodies. Recent work in other diseases has shown that functional distinctions of possible relevance to autoimmunity and immunodeficiency can be found among the B cell subsets defined by differential expression of the surface markers CD5 and CD45RA. Therefore, we have evaluated the CD5, CD45RA B cell subsets of both chronic alcoholics without evidence of active liver disease (AWLD), and alcoholics admitted for acute alcoholic liver disease (ALD). Mean B cell numbers were normal in AWLD, but significantly reduced in ALD. Analysis of B cells by three-colour flow cytometry in 20 patients and 29 controls revealed a sharp decrease in the percentage of alcoholics' B cells which were CD5+, 37.6% versus 16.3%, P < 0.000 01; absolute CD5+ B cell numbers were similarly reduced (58.9 cells/microliters versus 20.9; P = 0.0012). In addition to the loss of CD5+ B cells, there was a reduction in the percentage of B cells which are CD5- CD45RAhi, leaving many patients with a B cell profile which was predominantly CD19+ CD5- CD45RAlo. This subset appears phenotypically similar to the IgM-producing CD5- CD45RAlo subset described by others, and may be enriched for autoantibody-producing cells. One outlier patient was an ALD with 61% of B cells which were CD5+, which also is a profile consistent with increased autoantibody production.

An essential role for gp39, the ligand for CD40, in thymic selection

The interactions between CD40 on B cells and its ligand gp39 on activated T helper cells are known to be essential for the development of thymus-dependent humoral immunity. However, CD40 is also functionally expressed on thymic epithelial cells and dendritic cells, suggesting that gp39-CD40 interactions may also play a role in thymic education, the process by which self-reactive cells are deleted from the T cell repertoire. Six systems of negative selection were studied for their reliance on gp39-CD40 interactions to mediate negative selection. In all cases, when the antigen/superantigen was endogenously expressed (in contrast to exogenously administered), negative selection was blocked by loss of gp39 function. Specifically, blockade of gp39-CD40 interactions prevented the deletion of thymocytes expressing V beta 3, V beta 11, and V beta 12, specificities normally deleted in BALB/c mice because of the endogenous expression of minor lymphocyte-stimulating determinants. Independent verification of a role of gp39 in negative selection was provided by studies in gp39-deficient mice where alterations in T cell receptor (TCR) V beta expression were also observed. Studies were also performed in the AND TCR transgenic (Tg) mice, which bear the V alpha 11, V beta 3 TCR and recognize both pigeon cytochrome c (PCC)/IEk and H-2As. Neonatal administration of anti-gp39 to AND TCR Tg mice that endogenously express H-2As or endogenously produce PCC prevented the deletion of TCR Tg T cells. In contrast, deletion mediated by high-dose PCC peptide antigen (administered exogenously) in AND TCR mice was unaltered by administration of anti-gp39. In addition, deletion by Staphylococcus enterotoxin B in conventional mice was also unaffected by anti-gp39 administration. gp39 expression was induced on thymocytes by mitogens or by antigen on TCR Tg thymocytes. Immunohistochemical analysis of B7-2 expression in the thymus indicated that, in the absence of gp39, B7-2 expression was substantially reduced. Taken together, these data suggest that gp39 may influence negative selection through the regulation of costimulatory molecule expression. Moreover, the data support the hypothesis that, for negative selection to some endogenously produced antigens, negative selection may be dependent on TCR engagement and costimulation.

Modulation of T-cell adhesion markers, and the CD45R and CD57 antigens in human alcoholics

Direct and indirect evidence indicates that T cells are altered in alcoholics. The most commonly reported changes under direct examination have been consistent with an increased level of activation as reflected by shifts in the ratio of common leukocyte antigen isoforms expressed at the cell surface, by increases in the expression of class II antigen, or by alterations in the expression of various adhesion molecules. Functional evidence for T-cell abnormality includes loss of delayed hypersensitivity and a number of findings attributed to dysregulation of B cells by alcoholic T cells; these include the widely reported distrubances of immunoglobulin production in vivo and a range of abnormal responses when T and B cells are combined in vitro. Detailed flow cytometric examination of T cells from alcoholics with or without active liver disease reveals a significant loss of L-selectin CD8+ T cells, but not usually of CD4+ T cells. There is an inverse increase in the expression of CD11b on the CD8+ cells that have decreased L-selectin+ percentages. Both CD8+ and CD4+ T cells in alcoholics display a significant loss of the CD45RA isoform and a gain of cells exhibiting the CD45RO isoform. Other surface alterations include increased expression of CD57, a marker most commonly associated on T cells with conditions of chronic increased antigenic exposure. It is argued that these and other T-cell alterations in alcoholics are cytokine-driven in part and result in T-cell differentiation states that are functionally inappropriate.(ABSTRACT TRUNCATED AT 250 WORDS)

CpG motifs in bacterial DNA trigger direct B-cell activation

Unmethylated CpG dinucleotides are more frequent in the genomes of bacteria and viruses than of vertebrates. We report here that bacterial DNA and synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides induce murine B cells to proliferate and secrete immunoglobulin in vitro and in vivo. This activation is enhanced by simultaneous signals delivered through the antigen receptor. Optimal B-cell activation requires a DNA motif in which an unmethylated CpG dinucleotide is flanked by two 5' purines and two 3' pyrimidines. Oligodeoxynucleotides containing this CpG motif induce more than 95% of all spleen B cells to enter the cell cycle. These data suggest a possible evolutionary link between immune defence based on the recognition of microbial DNA and the phenomenon of 'CpG suppression' in vertebrates. The potent immune activation by CpG oligonucleotides has implications for the design and interpretation of studies using 'antisense' oligonucleotides and points to possible new applications as adjuvants.

The effect of in vivo IL-7 deprivation on T cell maturation

A number of previous studies have suggested a key role for interleukin 7 (IL-7) in the maturation of T lymphocytes. To better assess the function of IL-7 in lymphopoiesis, we have deprived mice of IL-7 in vivo by long-term administration of a neutralizing anti-IL-7 antibody. In a previous report (Grabstein, K. H., T. J. Waldschmidt, F. D. Finkelman, B. W. Hess, A. R. Alpert, N. E. Boiani, A. E. Namen, and P. J. Morrissey. 1993. J. Exp. Med. 178:257-264), we used this system to demonstrate the critical role of IL-7 in B cell maturation. After a brief period of anti-IL-7 treatment, most of the pro-B cells and all of the pre-B and immature B cells were depleted from the bone marrow. In the present report, we have injected anti-IL-7 antibody for periods of up to 12 wk to determine the effect of in vivo IL-7 deprivation on the thymus. The results demonstrate a > 99% reduction in thymic cellularity after extended periods of antibody administration. Examination of thymic CD4- and CD8- defined subsets revealed that, on a proportional basis, the CD4+, CD8+ subset was most depleted, the CD4 and CD8 single positive cells remained essentially unchanged, and the CD4-, CD8- compartment actually increased to approximately 50% of the thymus. Further examination of the double negative thymocytes demonstrated that IL-7 deprivation did, indeed, deplete the CD3-, CD4-, CD8- precursors, with expansion of this subset being interupted at the CD44+, CD25+ stage. The proportional increase in the CD4-, CD8- compartment was found to be due to an accumulation of CD3+, T cell receptor alpha, beta + double negative T cells. Additional analysis revealed that anti-IL-7 treatment suppressed the audition/selection process of T cells, as shown by a significant reduction of single positive cells expressing CD69 and heat stable antigen. Finally, the effects of IL-7 deprivation on the thymus were found to be reversible, with a normal pattern of thymic subsets returning 4 wk after cessation of treatment. The present results thus indicate a central role for IL-7 in the maturation of thymic-derived T cells.

Analysis of T-lymphocyte subpopulations in inflammatory bowel diseases by three-color flow cytometry

In order to better define changes in the relative proportion of peripheral blood T-lymphocyte subpopulations in patients with inflammatory diseases of the bowel, we performed simultaneous three-color fluorescence-activated cytometric (FACS) analysis using fluorophore-conjugated monoclonal antibodies with specificity for CD4, CD8, Leu 8, and CD45RA on 22 normal control subjects, 28 patients with Crohn's disease (CD), 15 patients with ulcerative colitis (UC), and 11 patients with intestinal inflammation secondary to etiologies other than inflammatory bowel disease (NIBD). This staining combination allowed enumeration of distinct T-cell subpopulations as follows: virgin CD4+, recall antigen helper T cells, nonspecific B-cell helper T cell, virgin CD8+, cytotoxic effector and suppressor effector and recall antigen cytotoxic T cells based on a synthesis of published functional analyses. No differences in the proportion of CD4+ or CD8+ cells or in the CD4+/CD8+ ratios were evident when UC and NIBD patients were compared to normal subjects. A significant reduction in the proportion of CD4+ cells and an increase in CD8+ cells was observed, however, in the CD group. When two-color analysis was performed, several significant differences in the proportions of circulating lymphocytes were seen. Specifically, these included significant increases in the number of CD4+, Leu 8- (P < 0.01) cells in all disease groups and an increase in CD4+, CD45RA+ cells in the NIBD group. Conversely, significant decreases in the proportions of CD8+, Leu 8+ (P < 0.01) cells were evident in the Crohn's disease group.(ABSTRACT TRUNCATED AT 250 WORDS)

Mice deficient for the CD40 ligand

To study the potential roles of CD40L in immune responses, we generated CD40L-deficient mice by gene targeting. Similar to the effects of CD40L mutations in humans (hyper-IgM syndrome), CD40L-deficient mice have a decreased IgM response to thymus-dependent antigens, fail altogether to produce an antigen-specific IgG1 response following immunization, yet respond normally to a T-independent antigen, TNP-Ficoll. Moreover, these mice do not develop germinal centers in response to thymus-dependent antigens, suggesting an inability to develop memory B cell responses. Although CD40L-deficient mice have low levels of most circulating immunoglobulin isotypes, they do not exhibit the spontaneous hyper-IgM syndrome seen in humans, at least up to 12 weeks of age. In summary, our study confirms the important role of CD40-CD40L interactions in thymus-dependent humoral immune responses and germinal center formation.

B-1 cells in systemic autoimmune responses: IgM+, Fc epsilon Rdull B cells are lost during chronic graft-versus-host disease but not in murine AIDS or collagen-induced arthritis

The potential role of B-1 cells (i.e. the CD5+ B cell and "sister" B cell subsets) in autoimmunity is controversial. CD5+ B cells have been shown to secrete antibodies of similar specificity as those found in many systemic autoimmune diseases; in addition, increases in CD5+ B cell frequency have been reported in patients suffering from rheumatoid arthritis, Sjögren's syndrome, myasthenia gravis, insulin-dependent diabetes mellitus and Hashimoto's thyroiditis. Whether these increases are due to expansion of B-1 lineage cells in the human or due to activation-induced expression of CD5 by conventional B cells is unclear. In the present study, we used three murine models of systemic autoimmunity: murine acquired immunodeficiency syndrome (MAIDS), chronic graft-versus-host disease (cGvHD), and collagen-induced arthritis (CIA) to determine whether increases in B-1 cell frequency are universally seen in models of autoimmunity which are mechanistically distinct. In contrast to the aforementioned human systemic autoimmune diseases which exhibit an increase in CD5+ B cell frequency, the percentage of CD5+ B cells declined in all three murine models of systemic autoimmune disease. Even though there was a decrease in the frequency of CD5+ B cells there was no change in the actual number of CD5+ B cells. Thus, the apparent decline in CD5+ B cell frequency was due to increases in either T cells, conventional Fc epsilon R+ B cells, or both. The only actual decline in a B cell subset was the loss of IgM+, Fc epsilon Rdull cells in both the spleen and peritoneal cavity of mice undergoing a chronic graft-versus-host reaction. Therefore, our data suggests that expansion of the B-1 subset does not occur as a general feature of murine systemic autoimmune disease. These observations, consistent with previous studies of Ig gene usage in autoreactive antibodies, support the view that expansion and differentiation of the CD5+ B cell subset is not a central event leading to autoantibody production.

Differential responses to Ig and class II-mediated signals in splenic B cell subsets from normal and autoimmune mice

B cells of mouse and human can be divided into distinct subpopulations, differing in distribution and phenotype. It is not known, however, whether B cell subsets respond similarly to signals mediated by cognate interactions with T cells, such as ligation of the B cell class II MHC molecule. Mouse splenic B cells proliferate in response to a combination of non-mitogenic anti-mu mAb, IL-4 and class II MHC-specific mAbs. In order to assess the response of B cell subpopulations to these signals, B cells were separated on the basis of CD23 expression. Previous studies have shown that CD23 expression is useful in distinguishing marginal zone from follicular B cells and peritoneal B1 from B2 B cells. B cells of both subsets responded to the combination of signals, but CD23- B cells showed a higher response. Splenic B cells were also purified from several strains of autoimmune mice, of interest because their disease features expansion of CD23- B cells and autoantibody production. While normal B cells showed no response to non-mitogenic anti-mu mAb alone, B cells from autoimmune mice showed a marked decrease in proliferation. Addition of IL-4 plus class II-specific mAbs restored increased proliferation. Again, responses were higher in CD23- than in CD23+ B cells. These findings suggest that CD23- B cells are especially responsive to signals delivered through class II and the IL-4 receptor. These signals may allow preferential rescue of CD23-B cells from antigen-mediated tolerance and result in their hyperexpansion in response to autoreactive T cells.

Tissue-specific expression of the human CD19 gene in transgenic mice inhibits antigen-independent B-lymphocyte development

CD19 is a B-cell-specific member of the immunoglobulin superfamily expressed from early pre-B-cell development until plasma cell differentiation. In vitro studies demonstrate that the CD19 signal transduction molecule can serve as a costimulatory molecule for activation through other B-lymphocyte cell surface molecules. However, much remains to be known regarding how CD19 functions in vivo and whether CD19 has different roles at particular stages of B-cell differentiation. Therefore, transgenic mice overexpressing the human CD19 (hCD19) gene were generated to determine whether this transgene would be expressed in a B-lineage-specific fashion and to dissect the in vivo role of CD19 in B-cell development and activation. Expression of the human transgene product was specifically restricted to all B-lineage cells and appeared early in development as occurs with hCD19. In addition, expression of hCD19 severely impaired the development of immature B cells in the bone marrow, with dramatically fewer B cells found in the spleen, peripheral circulation, and peritoneal cavity. The level of hCD19 expressed on the cell surface correlated directly with the severity of the defect in different transgenic lines. These results demonstrate that the hCD19 gene is expressed in a lineage-specific fashion in mice, indicating that the hCD19 gene may be useful for mediating B-lineage-specific expression of other transgene products. In addition, these results indicate an important role for the lineage-specific CD19 molecule during early B-cell development before antigen-dependent activation.

Fine T-cell subsets in alcoholics as determined by the expression of L-selectin, leukocyte common antigen, and beta-integrin

Alcoholics admitted to the hospital solely for detoxication have been studied by flow cytometry to evaluate changes in the surface markers of peripheral blood leukocytes. As we have shown previously, such patients have an elevated percentage of CD8hi lymphocytes that are HLA DR+; we now demonstrate that they also have striking alterations in the quantitative relationships of the fine T-cell subsets. Both CD4+ and CD8hi lymphocytes have a sharply reduced percentage of the L-selectin+ CD45RA+ subset, increased percentages of the CD45RA- subsets, and several other fine subset alterations. The fine subset profile suggests, according to current correlations of phenotype and function, that both CD4+ suppressor inducer and CD4-dependent CD8+ suppressor effector cells are reduced, whereas other subsets, including CD8+ CTL or their precursors, are increased in relative percentages. Some of the phenotypic changes are reversible over the several days following withdrawal. In other results, the percentage of CD8hi lymphocytes epxressing CD11b (beta-integrin) is shown to be reciprocal with the percentage expressing L-selectin both in normals and alcoholics. However, the regression function of CD11b vs. L-selectin on CD8hi cells is different for the alcoholics than for the normals, indicating an abnormality in the regulation of the expression of these two adhesion markers. Taken together, this abnormality of adhesion molecules and the fine subset alterations previously described indicate widespread changes in the peripheral lymphocytes of currently drinking alcoholics. These changes suggest functional deficiencies that may include alterations of lymphocyte traffic and other adhesion-dependent functions, and a shift in the balance of regulatory interactions.

Switching capacity of Fc epsilon RII-positive and -negative murine B cells

In previous studies, our laboratory demonstrated the utility of the low affinity IgE Fc receptor (Fc epsilon RII) in delineating a number of murine B cell subsets. In the spleen, the Fc epsilon RII is expressed on mature conventional B cells but is absent on marginal zone B cells. In the peritoneal cavity, the receptor is present on all conventional B cells, but is not expressed on fresh peritoneal Ly1/sister B cells. The studies in this report compared the ability of these B cell populations to isotype switch. Using a lipopolysaccharide (LPS)- and interleukin (IL)-4-driven system, sort-purified Fc epsilon RII-positive and -negative B cells from peritoneum and spleen were tested for switching to IgG1, IgE, and IgA. The results demonstrated that regardless of their source, Fc epsilon RII+ B cells produced significant levels of IgG1 and IgE. Similar results were obtained with Fc epsilon RII- (marginal zone) B cells obtained from spleen. In contrast, Fc epsilon RII- (Ly1/sister) peritoneal B cells were found to produce IgG1 and IgA, but were incapable of secreting significant levels of IgE. Further studies tested for LPS and IL-4-induced expression of Fc epsilon RII and Thy1 on the various B cell populations. These experiments demonstrated the induction of the Fc epsilon RII on all B cells, regardless of their initial resting levels. Additionally, Thy1 was found to be induced only on those B cell subsets capable of producing IgE. Taken together, the results demonstrate a correlation between IgE secretion and Thy1 expression, and no apparent correlation between the presence of the Fc epsilon RII and isotype commitment.

Inhibition of murine B and T lymphopoiesis in vivo by an anti-interleukin 7 monoclonal antibody

The effects of interleukin 7 (IL-7) on the growth and differentiation of murine B cell progenitors has been well characterized using in vitro culture methods. We have investigated the role of IL-7 in vivo using a monoclonal antibody that neutralizes IL-7. We find that treatment of mice with this antibody completely inhibits the development of B cell progenitors from the pro-B cell stage forward. We also provide evidence that all peripheral B cells, including those of the B-1 and conventional lineages, are derived from IL-7-dependent precursors. The results are consistent with the rapid turnover of B cell progenitors in the marrow, but a slow turnover of mature B cells in the periphery. In addition to effects on B cell development, anti-IL-7 treatment substantially reduced thymus cellularity, affecting all major thymic subpopulations.

Ontogeny and distribution of the murine B cell Fc gamma RII

The distribution and expression of the IgG FcRII (Fc gamma RII) on normal murine B cells was examined. Using multicolor flow cytometry, spleens from neonatal mice of increasing age and adult bone marrow were analyzed for expression of the Fc gamma RII. In addition, B cells from peripheral lymphoid organs, as well as panel of B cell tumors, were tested. The results demonstrate that the Fc gamma RII is expressed on all pre-B cells and immature B cells in the neonatal spleen and adult bone marrow, on all mature B cells in peripheral lymphoid organs, and on switched B cells in Peyer's patches. Furthermore, the Fc gamma RII was found to be present on B cell tumors representative of all stages of B cell maturation and differentiation. Taken together, the results indicate that Fc gamma RII is expressed during the entire lifetime of the B cell. In addition, examination of spleen cells from neonatal mice revealed a large number of pre-B cells, phenotypically defined as B220+, IgM-. These pre-B cells were present at birth, peaked in number between 2 and 3 wk of age, and became a minor population by day 30. Further phenotypic analysis of these cells demonstrated the expression of the BLA-1 and BP-1 Ag, and the lack of T cell and NK cell markers, thus confirming their assignment to the B cell lineage. Finally, the Fc gamma RII present on these pre-B cells was shown to be functional, by virtue of its ability to bind aggregated IgG.

Ontogeny and distribution of the murine B cell Fc gamma RII

The distribution and expression of the IgG FcRII (Fc gamma RII) on normal murine B cells was examined. Using multicolor flow cytometry, spleens from neonatal mice of increasing age and adult bone marrow were analyzed for expression of the Fc gamma RII. In addition, B cells from peripheral lymphoid organs, as well as panel of B cell tumors, were tested. The results demonstrate that the Fc gamma RII is expressed on all pre-B cells and immature B cells in the neonatal spleen and adult bone marrow, on all mature B cells in peripheral lymphoid organs, and on switched B cells in Peyer's patches. Furthermore, the Fc gamma RII was found to be present on B cell tumors representative of all stages of B cell maturation and differentiation. Taken together, the results indicate that Fc gamma RII is expressed during the entire lifetime of the B cell. In addition, examination of spleen cells from neonatal mice revealed a large number of pre-B cells, phenotypically defined as B220+, IgM-. These pre-B cells were present at birth, peaked in number between 2 and 3 wk of age, and became a minor population by day 30. Further phenotypic analysis of these cells demonstrated the expression of the BLA-1 and BP-1 Ag, and the lack of T cell and NK cell markers, thus confirming their assignment to the B cell lineage. Finally, the Fc gamma RII present on these pre-B cells was shown to be functional, by virtue of its ability to bind aggregated IgG.

CD5+ B cells are decreased in peripheral blood of patients with Crohn's disease

B cells bearing the CD5 surface marker comprise a substantial minority of the circulating lymphocyte population in healthy individuals. These recently described cells have been implicated in T-independent humoral responses, immunoregulation, and autoimmunity. We undertook to enumerate circulating CD5+ B cells by three-color fluorescence activated flow cytometry in 28 patients with Crohn's disease (CD). None of the CD patients were using immunosuppressive medication. The CD patients were subdivided into "inactive" and "active" groups based upon their Crohn's disease activity index (CDAI). Thirty-two normal subjects served as a control population. The percentage of CD19+ B cells was significantly reduced in both active and inactive CD patients as compared with normal controls (P less than or equal to 0.01). CD5+ B cells were likewise found to be significantly decreased in both inactive and active CD patients (P less than or equal to 0.01) as compared with normal controls. The proportion of CD5+ B cells was significantly lower in the peripheral blood of active as compared with inactive CD patients (P less than or equal to 0.05). The finding that CD5+ B cells are reduced in CD may provide an important clue to immunological dysfunction in inflammatory bowel disease and merits further study.

The expression of B cell surface receptors. III. The murine low-affinity IgE Fc receptor is not expressed on Ly 1 or 'Ly 1-like' B cells

The distribution of IgE FcR (Fc epsilon R)-positive and -negative B cells was examined in normal adult mice. Using three-color flow cytometry, the expression of the Fc epsilon R was analyzed on various B-cell subsets present in the peritoneum and spleen. The results demonstrate that in the peritoneal cavity, the Fc epsilon R is not expressed on the large majority of Ly 1+ B cells and Ly 1-, Mac 1+ sister B cells. The receptor is present, however, on the small number of conventional B cells residing in the peritoneum. Although interleukin 4 (IL-4) can increase the levels of the Fc epsilon R on conventional B cells, incubation of Ly 1 and sister B cells with IL-4 did not result in the expression of the Fc epsilon R. When examining B cells present in the spleen, a small subset of B cells was consistently found to be Fc epsilon R-. These Fc epsilon R- cells were IgM-bright, IgD-dull and largely Ly 1- and Mac 1-negative. Staining of splenic tissue sections revealed that the Fc epsilon R- B cells were primarily localized to the marginal zones, whereas the Fc epsilon R+ B cells were found in the follicles. Taken together, the results indicate that the Fc epsilon R may be a useful marker in delineating the various B-cell subsets. In the peritoneum, the Fc epsilon R appears to discriminate conventional B cells from those of the Ly 1/sister lineage, and in the spleen it is likely to distinguish resting follicular B cells from Ly 1/sister and marginal zone B cells.

Several types of adherent cells elaborate a dialyzable lymphopoietic cofactor (Abelson Growth Promoter)

We have cloned a stromal cell from mouse bone marrow selected on the basis of its ability to promote the growth of an Abelson virus-transformed pre-B cell line. These stromal cells have smooth muscle features, and the ultrafiltrate of stromal cell-conditioned medium has proliferative effects on all feeder layer-responsive mouse pre-B cell lines tested, as well as on normal pre-B cells. One of these low MW substances is a protease-resistant factor with an MW of approximately 450 Da which we designate Abelson Growth Promoter (AGP). AGP was initially characterized as an activity which promotes the growth of Abelson virus-transformed mouse pre-B cells, but it also promotes the growth of a ras-transformed pre-B cell line as a single agent and in synergistic fashion with recombinant interleukin (IL) 7. AGP as a single agent has no effect on normal pre-B cells, which have a brisk response to IL-7. In contrast, transformed pre-B cells display a blunted response to IL-7. We propose that AGP plays a role in normal lymphopoiesis by expanding clones of pre-B cells which have been activated by other stromal cell-derived signals, such as IL-7, and directly promotes the growth of nascently transformed pre-B cells.

Dissociation of tissue destruction induced by cytolytic T cells in vivo and cytotoxicity as measured in vitro

Two forms of local cutaneous graft-versus-host reactions were used to examine the in vivo activity of cytolytic T cells in a large number of antigen systems and mouse strain combinations. In immune lymphocyte transfer reactions (TrRs), CTL were injected intradermally into allogeneic hosts to which they were sensitized; in bystander reactions (ByRs), CTL were mixed with target cells and the mixture injected into hosts syngeneic to the CTL. Both reactions frequently culminate in full-thickness skin destruction. However, CTL highly active in cell-mediated lympholysis assays in vitro sometimes failed to induce significant reactions in vivo, and CTL with negligible CML activity often induced severe, necrotizing lesions. In addition, Clone 58, a non-MHC-specific CD8+ clone that originated from cells extracted from a sponge matrix allograft, lost its CML activity but continued to induce necrotizing TrRs and ByRs. Insofar as these reactions may exemplify the specific (TrR) and nonspecific (ByR) tissue injury that occurs in the rejection process, these findings question the reliability of CML for predicting the ability of CTL to induce the tissue destruction seen in allograft rejection.

IgA-induced avidity maturation of IgA Fc receptors on murine T lymphocytes

The analysis of 30 well characterized murine T lymphocyte populations using a cytofluorometric IgA binding assay has identified many populations that are constitutive and/or inducible for IgA receptor expression, and has identified two distinct mechanisms by which IgA up-regulates the IgA-binding properties of murine T cells. Studies with lymphomas, hybridomas, Ag-specific clones and activated normal splenic T cells identified many examples of CD4 and CD8 lineage cells that constitutively expressed IgA receptors. T cell populations that constitutively expressed IgA receptors exhibited enhanced IgA binding after incubation with oligomeric IgA for 18 h. The IgA-induced up-regulation of IgA binding resulted from two distinct processes: 1) an increase in the number of surface membrane IgA binding sites and 2) an increase in the avidity of IgA binding without a change in the number of binding sites. The IgA-induced avidity increase was reflected by a 5- to 10-fold decrease in the apparent Kd. Depending on the T cell population examined the enhanced binding of IgA involved one or both of these mechanisms. T cell populations that did not constitutively express IgA receptors failed to bind IgA after prolonged incubation with oligomeric IgA suggesting that if such cells can express IgA receptors they require other signals to induce their expression. Consistent with this possibility is the finding that resting splenic T cells did not bind IgA but their activation with Con A or mAb anti-T3 resulted in high level expression of IgA receptors. These studies have identified multiple distinct mechanisms that alter the IgA-binding properties of murine T cells and are discussed in terms of their possible physiologic significance.

IgA-induced avidity maturation of IgA Fc receptors on murine T lymphocytes

The analysis of 30 well characterized murine T lymphocyte populations using a cytofluorometric IgA binding assay has identified many populations that are constitutive and/or inducible for IgA receptor expression, and has identified two distinct mechanisms by which IgA up-regulates the IgA-binding properties of murine T cells. Studies with lymphomas, hybridomas, Ag-specific clones and activated normal splenic T cells identified many examples of CD4 and CD8 lineage cells that constitutively expressed IgA receptors. T cell populations that constitutively expressed IgA receptors exhibited enhanced IgA binding after incubation with oligomeric IgA for 18 h. The IgA-induced up-regulation of IgA binding resulted from two distinct processes: 1) an increase in the number of surface membrane IgA binding sites and 2) an increase in the avidity of IgA binding without a change in the number of binding sites. The IgA-induced avidity increase was reflected by a 5- to 10-fold decrease in the apparent Kd. Depending on the T cell population examined the enhanced binding of IgA involved one or both of these mechanisms. T cell populations that did not constitutively express IgA receptors failed to bind IgA after prolonged incubation with oligomeric IgA suggesting that if such cells can express IgA receptors they require other signals to induce their expression. Consistent with this possibility is the finding that resting splenic T cells did not bind IgA but their activation with Con A or mAb anti-T3 resulted in high level expression of IgA receptors. These studies have identified multiple distinct mechanisms that alter the IgA-binding properties of murine T cells and are discussed in terms of their possible physiologic significance.

Expression of B cell surface receptors. II. IL-4 can accelerate the developmental expression of the murine B cell IgE Fc receptor

The ability of IL-4 to influence the developmental expression of the murine B cell IgE Fc receptor (Fc epsilon R) was examined. Spleen cells from neonatal mice of increasing age were incubated overnight with IL-4 and subsequently examined with multicolor flow cytometry. The results demonstrate that IL-4 can significantly increase the number of maturing B cells which express the Fc epsilon R. This effect was only seen however, on those neonatal B cells which already displayed surface IgD. Splenic B cells which were IgM+, IgD- failed to express the Fc epsilon R when treated with IL-4, even though they responded by increasing their level of class II Ag expression. Further experiments showed that the inability of IgD- immature B cells to express the Fc epsilon R could not be entirely explained by their assignment to the Ly-1 lineage. Taken together, these results indicate that IL-4 can accelerate the developmental expression of the B cell Fc epsilon R, but only on those B cells that are mature enough to express IgD.

Expression of B cell surface receptors. II. IL-4 can accelerate the developmental expression of the murine B cell IgE Fc receptor

The ability of IL-4 to influence the developmental expression of the murine B cell IgE Fc receptor (Fc epsilon R) was examined. Spleen cells from neonatal mice of increasing age were incubated overnight with IL-4 and subsequently examined with multicolor flow cytometry. The results demonstrate that IL-4 can significantly increase the number of maturing B cells which express the Fc epsilon R. This effect was only seen however, on those neonatal B cells which already displayed surface IgD. Splenic B cells which were IgM+, IgD- failed to express the Fc epsilon R when treated with IL-4, even though they responded by increasing their level of class II Ag expression. Further experiments showed that the inability of IgD- immature B cells to express the Fc epsilon R could not be entirely explained by their assignment to the Ly-1 lineage. Taken together, these results indicate that IL-4 can accelerate the developmental expression of the B cell Fc epsilon R, but only on those B cells that are mature enough to express IgD.

Immunoglobulin (Fc) receptors on murine T- and B-lymphocytes: investigations using tumor models

Lymphoid tumors are productive experimental models for the study of lymphocyte immunoglobulin receptors. Investigations with Fc receptor expressing lymphoid tumor cells have generated much useful information about: (a) the developmental expression of the different classes of Fc receptors on lymphoid cells of the T- and B-lineages; (b) the biochemical steps involved in the regulation of Fc receptor expression on lymphoid cells; (c) the structures of lymphoid cell Fc receptors and their genes; (d) the signals that induce alterations in the expression of Fc receptors on lymphoid cells; and (e) the molecular specificity of the binding of immunoglobulin to lymphoid cells Fc receptors. In addition, tumors that secrete immunoglobulins are providing useful models for analysis of the mechanisms by which B-cells influence Fc receptor expression and function on T-cells. An interesting, bi-directional immunoregulatory circuit involving Fc epsilon R+ host T-cells and IgE-secreting hybridoma cells has been identified that could prove useful in the analysis of the regulation of epsilon heavy chain expression. The studies discussed in this article and elsewhere in this volume serve to emphasize that, in addition to being clonal sources of key molecules such as Fc receptors and their messenger RNAs, lymphoid tumor cells that express Fc receptors are powerful and unique experimental models for investigating the developmental biology, regulation and function of lymphocyte Fc receptors.

The expression of B cell surface receptors. I. The ontogeny and distribution of the murine B cell IgE Fc receptor

The ontogenic appearance and lymphoid tissue distribution of the murine B cell IgE FcR (Fc epsilon R) was examined. Flow cytometry was utilized to study the expression of the Fc epsilon R on splenic B cells from mice of increasing age, as well as B cells from various lymphoid organs. A large panel of B cell tumors was also screened for the presence of the Fc epsilon R. The results demonstrate that the Fc epsilon R appears very late in B cell development, and is preceded in appearance even by IgD. In adult animals, the Fc epsilon R was found to be expressed on virtually all mature IgM, IgD bearing B cells, whether taken from the spleen, lymph nodes, or Peyer's patches. Further examination showed that B cells which had switched to express an isotype other than IgD, appeared to no longer display the Fc epsilon R. When surveying a variety of B cell tumors, the Fc epsilon R was found to be present on WEHI 279, an IgM, IgD-bearing lymphoma. The receptor was not found on pre-B cell, immature B cell, switched B cell, or secreting B cell tumors. Taken together, these results indicate that the B cell Fc epsilon R is expressed predominantly on mature, virgin B cells, and is lost after activation and switching.

The expression of B cell surface receptors. I. The ontogeny and distribution of the murine B cell IgE Fc receptor

The ontogenic appearance and lymphoid tissue distribution of the murine B cell IgE FcR (Fc epsilon R) was examined. Flow cytometry was utilized to study the expression of the Fc epsilon R on splenic B cells from mice of increasing age, as well as B cells from various lymphoid organs. A large panel of B cell tumors was also screened for the presence of the Fc epsilon R. The results demonstrate that the Fc epsilon R appears very late in B cell development, and is preceded in appearance even by IgD. In adult animals, the Fc epsilon R was found to be expressed on virtually all mature IgM, IgD bearing B cells, whether taken from the spleen, lymph nodes, or Peyer's patches. Further examination showed that B cells which had switched to express an isotype other than IgD, appeared to no longer display the Fc epsilon R. When surveying a variety of B cell tumors, the Fc epsilon R was found to be present on WEHI 279, an IgM, IgD-bearing lymphoma. The receptor was not found on pre-B cell, immature B cell, switched B cell, or secreting B cell tumors. Taken together, these results indicate that the B cell Fc epsilon R is expressed predominantly on mature, virgin B cells, and is lost after activation and switching.

Effect of B cell stimulatory factor-1 (interleukin 4) on Fc epsilon and Fc gamma receptor expression on murine B lymphocytes and B cell lines

Culture of murine splenic B cells with interleukin 4 (IL-4) caused the up-regulation of the lymphocyte Fc receptor for immunoglobulin E (IgE) (Fc epsilon R) over a similar dose range as required for Ia up-regulation. However, the expression level of the Fc receptor for immunoglobulin G (Fc gamma R) did not increase, rather IL-4 caused a slight but consistent decrease in the Fc gamma R level on the B cells. Fc epsilon R+ B hybridoma cells also responded to IL-4 by exhibiting increased Fc epsilon R expression; with the hybridoma cells Fc gamma R levels were unaffected. IL-4 caused an increase in the number of Fc epsilon R per cell and the highest levels of expression were obtained by having both IgE and IL-4 present in the culture. The specificity of the increase was demonstrated by blocking IL-4-mediated actions with monoclonal anti-IL-4 (11B11). Experiments following the incorporation of [35S]methionine into the Fc epsilon R demonstrated that IL-4 increased the rate of Fc epsilon R biosynthesis; this provides an explanation for the IL-4-induced increase in Fc epsilon R expression. IL-4, unlike IgE, had no effect on the rate of degradation of the Fc epsilon R. Interferon-gamma (IFN-gamma) totally abrogated IL-4-mediated Fc epsilon R up-regulation; at the same concentration of IFN-gamma Ia up-regulation is also suppressed, although not as effectively. IFN-gamma was shown to directly suppress Fc epsilon R synthesis, thereby explaining the inhibitory action on Fc epsilon R levels. Finally, it was shown that 11B11 inhibited the increased expression of Fc epsilon R on B cells obtained from mice during the early, but not the late, stages of Nippostrongylus brasiliensis infection. This latter finding suggests that the high Fc epsilon R levels seen early in parasite infections are dependent upon IL-4. The results overall provide further insight into the biologic activities of IL-4.