Immunoglobulin VH gene expression in Ly-1+ and conventional B lymphocytes

B cell development in mice

The development and establishment of the B Cell Repertoire is the net result of both genetic and environmental forces. The primary event at the genetic level is Ig gene rearrangement resulting in numerous possible combination of genes which can be further modified by somatic events such as N segment addition and somatic mutation. Environmental forces in the form of self and exogenous Ags also shape the repertoire by positively or negatively selecting B cells according to the specificity of their Ig receptors. These are dynamic processes beginning with the earliest expression of immunoglobulins in fetal life and continuing throughout life. In this review we discuss the genetic and selective mechanisms responsible for differences in the early immune system compared to that of the adult.

The primary antibody repertoire of normal, immunodeficient and autoimmune mice is characterized by differences in V gene expression

During the last decade, the structure and organization of the immunoglobulin heavy and light chain locis have been defined in mice and humans. Studies on VH gene expression at different stages of development, in different organs and disease states have provided useful insight into the construction of a primary antibody repertoire in mice. Clearly, 3'VH genes 7183, Q52 and Vh11, which are conserved during evolution, are preferentially expressed during early development of the B-lymphocyte repertoire. A preferential use for the V kappa 4 gene family is evident during early B-cell development. The initial development of the primary antibody repertoire is therefore influenced by a restricted set of VH and V kappa gene elements. The restricted B-cell repertoire is subsequently normalized in the periphery, as revealed by stochastic VH gene expression, as a result of exposure to environmental antigens. Obviously, the peripheral B-cell pool characterized by stochastic VH gene expression is selectively replenished by newly generated B cells in bone marrow that preferentially expresses 3'VH genes. The V kappa genes are, however, expressed in a non-random manner in the neonatal and adult B-lymphocyte repertoire that is probably related to VH and V kappa association dynamics and/or positive or negative selection. Interestingly, these characteristics of neonatal and adult primary repertoire are noted in both B1 and B2 lymphocytes. No remarkable age-related differences are evident for VH and V kappa gene expression. In healthy mice, both the mitogen responsive (available) and unstimulated (expressed) B-cell repertoire show similar VH gene expression. Interestingly, VH gene expression varies in different organs which may reflect, or occur as a result of, the specialized function of each organ. For example, J558 gene expression is higher in the peripheral LN where B cells continuously encounter exogenous antigens. The skewed VH and V kappa gene expression noted in immunodeficient and autoimmune lupus-prone mice reflects the impairment of the primary antibody repertoire associated with immunodeficiency and autoimmune disorders.

VH-gene family dominance in ageing mice

The cellular composition and VH-gene family repertoire were compared in different B-cell compartments from young adult (8-12 weeks) and old (18-24 months) C57BL/6 and BALB/c mice. Ageing mice were found to have a higher frequency of peripheral mature B cells utilizing genes from a single VH-gene family. While in each individual old C57BL/6 mice cells expressing the VH J558 gene family consistently were over-represented, a marked individual variation was observed in old BALB/c mice with increased frequency of either the VH J558, Q52 or J606 families. Aged mice were found also to have a reduced number of bone-marrow pre-B cells and an augmented number of splenic Ig-secreting cells. These results suggest that old mice express less diversified antibody repertoires possibly as a consequence of reduced input from precursors and increased peripheral selection, which may be responsible for the progressive establishment of immunodeficiency.

Maintenance of CD5+ B cells at an early developmental stage by interleukin-5: evidence from immunoglobulin gene usage in interleukin-5 transgenic mice

We have characterized the development and expansion of CD5+ B cells in interleukin-5 (IL-5) transgenic mice in terms of autoantibody production and immunoglobulin gene usage. CD5+IL-5R alpha+ B cells maintained in the presence of IL-5 secreted fewer autoantibodies and had fewer N nucleotides at the 3' end of the D elements compared with CD5- B cells. The reduction in nucleotides, along with the finding that CD5+IL-5R alpha+ B cells in IL-5 transgenic mice use Q52 families more frequently than age-matched control B cells, also suggests that these cells have the characteristics of fetus-type B cells and represent an early stage of B-cell development. All of the VH11 families were expressed with JH1 and the Q52 families were frequently expressed with JH1. Furthermore, JH proximal DQ52 was frequently used in IL-5 transgenic mice. All of these characteristics in terms of immunoglobulin gene usage have been described for CD5+ B cells. These results suggest that IL-5 maintains CD5+ B cells that have a fetus-type of immunoglobulin gene usage. This cytokine could be responsible for prolonging the life span of immature CD5+ B cells, which subsequently mature to CD5- B cells that secrete polyreactive natural antibodies.

The majority of human tonsillar CD5+ B cells express somatically mutated V kappa 4 genes

We have fractionated human tonsillar B cells on the basis of CD5 expression and determined the nucleotide sequences of immunoglobin light chain variable (V) regions encoded by the single member of the V chi 4 gene family in both CD5+ and CD5- populations. The majority of cDNA from both CD5+ and CD5- B cells populations harbored somatic mutations. Thus, human tonsillar CD5+ B cells, unlike their murine counterparts, are capable of activating their somatic hypermutation mechanism, resulting in the accumulation of somatic mutation in the VL regions.

VH gene family utilization of anti-acetylcholine receptor antibodies in experimental autoimmune myasthenia gravis

The immunoglobulin heavy chain (VH) gene family usage in experimental autoimmune myasthenia gravis (EAMG) model was investigated by RNA slot blot hybridization using VH gene family specific probes. Anti-acetylcholine receptor (AChR) monoclonal antibodies (mAbs) isolated from susceptible C57BL/6 and resistant BALB/c mice were found to be encoded by VH genes from at least six different families. The Vgam3.8 family was overrepresented in alpha-bungarotoxin blocking mAbs. Expression of cross-reactive idiotypes by anti-AChR mAbs was irrespective of the VH gene family usage. Strain dependent differences in susceptibility for EAMG were not reflected in an aberrant VH gene family usage of anti-AChR mAbs.

Functional and molecular characterization of single, (4-hydroxy-3-nitrophenyl)acetyl (NP)-specific, IgG1+ B cells from antibody-secreting and memory B cell pathways in the C57BL/6 immune response to NP

We have used multiparameter flow cytometry to identify a population of IgG1+ IgM- antigen-specific B cells which emerges in spleens of C57BL/6 mice following immunization with the hapten, (4-hydroxy-3-nitrophenyl)acetyl (NP). Characterization of the specificities of IgG1 antibodies produced by single, sorted IgG1+ NP+ cells in both Elispot assays and in microcultures containing lipopolysaccharide, interleukin (IL)-2, IL-4 and IL-5 indicates that the splenic IgG1+ NP+ B cell population includes both IgG1 anti-NP antibody-secreting cells and non-secreting, IgG1+ memory B cells. Each functionally discrete population of IgG1+ B cells expresses a distinctive surface phenotype defined by a wide range of B cell markers. In particular, antibody-secreting, IgG1+ cells were uniquely identified by co-expression of the matrix receptor, syndecan. The NP-specific B cell population emerging in the day 7 primary response was assessed for clonotypic diversity by amplification and direct sequencing of the rearranged V186.2 heavy chain variable region gene expressed by single, ex vivo IgG1+ NP+ lambda+ B cells. Memory B cell clones, distinguished by junctional diversity, carried either no mutation or a single mutation within rearranged V186.2, suggesting isolation of these cells at the onset of the hypermutation mechanism. This novel approach, therefore, allows the direct and unambiguous identification and characterization of individual B cell clonotypes during their initial selection and activation in antibody responses in vivo.

Production of 17.2.25 mu transgenic and endogenous immunoglobulin in X-linked immune deficient mice

In M54 mice transgenic for a completely rearranged mu(a) heavy chain there is a decrease in total B cells and the rearrangement of endogenous immunoglobulin genes is partially inhibited. Surprisingly, however, endogenous immunoglobulin gene rearrangement and significant heavy chain polypeptide production does occur. We tested the hypothesis that only CD5+ B cells produce endogenous immunoglobulin by taking advantage of the fact that X-linked immune deficient (xid) mice normally are deficient in CD5+ B cells. We found that the frequency of CD5+ splenic B cells was similar in XxidY transgenic and non-transgenic F1 males, and in XxidX transgenic and non-transgenic F1 females. In both XxidX and XxidY transgenic F1 mice some, but not all, splenic B cells are CD11b+. There was a striking deficit of splenic B cells expressing endogenous immunoglobulin in XxidY transgenic mice, although this was not true for peritoneal cells. Thus, the introduction of the 17.2.25 mu transgene does not prevent the development of CD5- B cells nor does it limit endogenous immunoglobulin gene arrangement and expression solely to CD5+ B cells. However, in mice capable of expressing B cell surface CD5 or CD11 this transgene can lead to expansion of the fraction of B cells positive for these molecules. We conclude that while the introduction of the 17.2.25 mu transgene alters the frequencies of B cell populations, maturation is not limited to one subpopulation.

Repertoire of CD5+ and CD5- cord blood B cells: specificity and expression of VH I and VH III associated idiotopes

Epstein-Barr (EBV)-immortalized B cell clones were established from CD5+ and CD5- cord blood B cells separated by flow cytometry. We have previously shown that IgM from many of the clones was polyreactive, exhibiting reactivity with a number of autoantigens. In this study, IgM produced by the clones was analysed by MoAb for the expression of cross-reactive idiotypes (CRI) associated with rheumatoid factor paraproteins and from defined VH and V kappa subgroups of immunoglobulin heavy and light chains. IgM produced by clones established from CD5+ and CD5- B cells expressed the VH I associated idiotope G8. Furthermore, IgM produced by both sets of clones exhibited a similar frequency of VH III heavy chain subgroup expression, as determined by reactivity with staphylococcal protein A (SpA) and VH III-associated CRI expression (B6 and/or D12). In contrast, expression of the V kappa III-associated 17.109 CRI was significantly higher in IgM antibodies produced by clones established from CD5+ compared with the CD5- clones (32 versus 5%: P less than 0.05). Analysis of the VH and VL subgroup expression by IgM produced by the CD5+ and CD5- cord blood clones, and their autoantigen reactivity profile did not reveal restriction or selection within CD5+ and CD5- populations. However, our data suggest that differences may exist in the expression of certain germ-line genes between CD5+ and CD5- cord blood B cells and might indicate an expansion of CD5+ B cells within the fetal environment.

Loss of CD23 is a consequence of B-cell activation. Implications for the analysis of B-cell lineages

When splenic CD5- B cells are stimulated with antiimmunoglobulin they become CD5+ and have a prolonged in vitro life. Further treatment with IL-6 induces a loss of surface CD23 and IgD; that is, they resemble freshly isolated peritoneal CD5+ cells. These data suggest that the CD5 phenotype is induced after sIg-mediated B-cell activation. Additional support for this view arises from the observation that the loss of CD23 and IgD can be induced by another activation inducer, LPS, although in this case CD5 is not expressed. Thus, activation by anti-Ig plus IL-6 or by LPS induces CD23 loss. Consistent with the hypothesis that the loss of CD23 is a consequence of activation, we now report that the surface expression of CD23 varies inversely with the amount of total cellular RNA. We also find both CD23 positive and negative B cells among freshly isolated splenic CD5- B cells. In young mice a proportion of small splenic CD5+ B cells are CD23+, providing additional evidence that CD23 is present on all B cells prior to activation. A comparison of the features of CD5+ B cells and the antibody responses to thymus-dependent and thymus-independent antigens leads us to hypothesize that the CD5 phenotype arises as a consequence of thymus-independent type 2 (TI-2) stimulation. The relationship of CD5 expression to B-cell lineage (fetal vs. adult bone marrow) is discussed.

Specificity and idiotope expression of IgM produced by CD5+ and CD5- cord blood B-cell clones

Epstein-Barr virus (EBV)-immortalized monoclonal B-cell lines were established from CD5+ and CD5- cord-blood B cells. IgM from many of both CD5+ and CD5- clones reacted with IgG-Fc, ssDNA, and a variety of other autoantigens. More CD5+ B cells that used light chains of the kappa isotype reacted with IgG-Fc and ssDNA than kappa-bearing CD5- B cells. Because many of the clones reacted with IgG-Fc, they were analyzed for the expression of cross-reactive idiotypes (CRI) associated with rheumatoid factor and cold agglutinin paraproteins using murine antibodies (mAb) recognizing V kappa and VH subgroup-associated determinants. Expression of the V kappa IIIb sub-subgroup-associated idiotope recognized by 17.109 mAb was expressed at significantly higher frequency (32%; p less than 0.05) and IgM antibodies derived from the CD5+ compared with the CD5- clones (5%). Both CD5+ and CD5- clones expressed the RF paraprotein-associated idiotope recognized by G8 mAb to the same extent. Similar results were obtained using binding to SpA as a marker of VH III family usage. Furthermore, no differences in frequency of expression of RF paraprotein-associated idiotopes recognized by B6 and/or D12, and characteristic of some antibodies using VH III family genes, were found between the CD5+ and CD5- populations. Although a higher than expected frequency of VH IV-gene expression was demonstrated (around 30%) in both CD5+ and CD5- cells, there were differences in expression of CRI recognized by mAb Lc1 and R2.1A2 with specificities for two VH IV subfamilies. While some CD5+ and CD5- clones were identified in which their IgM reacted with mAb Lc1, only CD5+ clones were recognized by another mAb R2.1A2. Analysis of the relationships between antigen specificities and V kappa- and VH-family gene usage indicated that auto- or polyreactivity was not associated with V kappa III nor any particular VH family. The higher frequency of the V kappa IIIb sub-subgroup-associated idiotope recognized by 17-109 in the CD5+ clones and the association of CD5+ B cells with the VH IV subfamily recognized by mAb R2.1A2 and 9G4 may suggest that CD5+ B cells in cord blood are expanded as a result of recruitment within the fetal environment.

Origin of CD5+ B cells and natural IgM-secreting cells: reconstitution potential of adult bone marrow, spleen and peritoneal cells

The bulk of natural IgM secretion is currently attributed to peritoneal CD5+ B cells and their progeny, believed to be independent of adult bone marrow precursors. We have compared the capacity of peritoneal or splenic cells from normal adult mice to generate serum IgM after transfer into allotype-congenic, irradiated and bone marrow-protected mice. Recipients of either cell population produced donor-allotype IgM-secreting cells in the spleen, and had donor-derived serum IgM. In both cases as well, recipient IgM secretion recovered to control levels. Since the spleen cell-derived natural IgM production could result from expansion of CD5+ B cells present in the inoculum, we next investigated the ability of Ig- bone marrow (BM) cells (Ig- BM) to reconstitute natural IgM secretion in irradiated mice. This cell population was most efficient in reconstituting donor-derived IgM secretion. The origin and phenotype (IgM, CD5) of B cells present in spleen and peritoneum of recipient mice were also analyzed. In agreement with the high level of donor IgM-secreting cells, transfers of splenic and Ig- BM cells fully reconstitute donor B cells in spleen and peritoneum and inhibit reconstitution from host origin. In contrast, donor peritoneal cells reconstitute B cells very poorly in spleen and allow for reconstitution by host cells. Furthermore, Ig- BM cells as well as splenic or peritoneal donor cells, all reconstitute CD5+ B cells in the peritoneum of recipient mice. Interestingly, the fraction of IgM+ cells of each allotype that differentiate to IgM secretion varies widely, but normal levels of IgM are established even when the number of donor B cells present in the animal is very limited.

Regulatory aspects of clonally expanded B-1 (CD5+ B) cells

B-1 (CD5+ B) cells appear early in ontogeny, produce mainly unmutated polyreactive antibodies, and are capable of self-renewal. B-1 cells clonally expand with age and are the malignant cell in chronic lymphocytic leukemia. In this report immunological analysis of B-1 malignancies in NZB mice, a murine model of chronic lymphocytic leukemia, is related to current information on B-1 cells. B-1 clones from NZB mice produce high levels of interleukin-10, detected at the RNA level by semi-quantitative polymerase chain reaction. In addition, the B-1 malignant clones in NZB mice and their hybrids, are negative for B220/6B2 expression, the B-specific antigenic form of CD45 which is a membrane-associated phosphatase involved in lymphocyte activation. Both the autocrine production by B-1 cells of interleukin-10 and altered CD45 expression may be responsible for the clonal expansion of these cells, as well as the accompanying T cell expansion. We report the establishment of an in vitro cytotoxic CD8+ T cell line derived from an NZB with a B-1 malignancy. The effect of B-1 cell-derived interleukin-10 on subsets of T lymphocytes may account for the immunoregulatory properties of B-1 cells. In addition, the NZB malignancies were also characterized for immunoglobulin variable region sequence and antigen specificity. The B-1 malignancies produced immunoglobulin derived from unmutated germline sequences with no N base substitutions. It appears that both the immunoglobulin and interleukin-10 produced by the B-1 malignant cell in NZB mice may have immunoregulatory properties. A study of B-1 malignancies may shed light on the immunoregulatory properties of non-clonally expanded normal B-1 cells.

Enhancement of mucosal antibody responses to Salmonella typhimurium and the microbial hapten phosphorylcholine in mice with X-linked immunodeficiency by B-cell precursors from the peritoneal cavity

The observation that approximately half of the B cells in the murine intestinal lamina propria are derived from peritoneal CD5 B-cell precursors raises the question of their contribution to mucosal protection. Using mice with X-linked immunodeficiency which are deficient in CD5+ B cells, we showed that they mount little serum and virtually no intestinal immunoglobulin M (IgM), IgG, and IgA antibody responses following oral inoculation with live Salmonella typhimurium. Nonresponsive Xid mice were reconstituted with responsive CBA/Ca donor cell preparations which were constitutively enriched or depleted of CD5 B-cell precursors. Reconstitution of irradiated Xid mice with CD5 B-cell-deficient bone marrow from CBA/Ca donors marginally improved IgM responses in the intestinal mucosa but had no effect on IgG or IgA in response to oral immunization with live S. typhimurium. Whenever Xid mice were reconstituted with donor cells from the peritoneal cavity, which are enriched for CD5 B-cell precursors, strong IgA and in some cases IgG responses in the intestinal mucosa were stimulated in response to oral immunization. When mucosal and serum antibody responses were compared, the peritoneal donor cells again reinstated maximal serum antibody responses to S. typhimurium. Serum and mucosal responses to the bacterial hapten phosphorylcholine could be induced in Xid mice after immunization with S. typhimurium or hapten-carrier conjugates but only following reconstitution with donor cells containing CD5 B-cell precursors. These observations suggest that different lymphoid compartments are enriched for regulatory or effector cells which vary in their contributions to the mucosal antibody response against epitopes on S. typhimurium.

Comparative expression of adult and fetal V gene repertoires

A hallmark of the immune system is the extraordinary diversity associated with antibodies. This is made possible by a series of genetic rearrangements involving variable region gene segments. Considerable detail is known about these genetic mechanisms except for the enzymatic machinery involved. An important question in studies of the generation of diversity is whether V genes are selected for rearrangement mainly in a random manner or selected by particular developmental rules. Past studies have indicated that the acquisition of fetal and neonatal specificity repertoires is a nonrandom process. In this report, we review our studies that directly compare the adult and fetal/neonatal V gene repertoires. The evidence suggests that the adult repertoire is more diverse with indications of a random use of VH gene families. However, whether V genes are indeed randomly used in the adult remains to be clarified at the VH gene member level. The fetal repertoire, on the other hand, appears nonrandom in V gene usage. In addition, the fetal repertoire is mostly germline encoded with little evidence of junctional diversity. Taken together, the results indicate different rules for generation of the adult and fetal repertoires, findings most likely explain by distinct B cell subsets and B cell progenitors at early stages in ontogeny.

Biased VH gene expression in murine CD5 B cells results from age-dependent cellular selection

Flow cytometry-purified, peritoneal and splenic CD5+ and CD5- B cells from neonatal and adult C57BL/6 mice were studied for expression of VH and Vx gene families in RNA colony blot assays, and for frequencies of clones secreting antibodies to bromelain-treated mouse red blood cells (BrMRBC), single-stranded DNA, trimethyl ammonium and bovine gamma-globulin, by limiting dilution. The results show few overall differences between the two B cell subsets, which both manifest ontogenic D-proximal VH preferences that are lost with age. Biased VH11 expression in CD5 B cells is high in adult peritoneum and spleen but absent in newborns. It only partly correlates with the selection of anti-BrMRBC reactivity, which is considerably higher in peritoneum than in spleen. No particular Vx bias was observed in any of the populations studied with the possible exception of Vx22 in peritoneal CD5+ B cells. We conclude that the antibody repertoire expressed by peritoneal CD5+ B cells of adult mice is not the result of a genetic program, but rather the consequence of local, age-dependent cellular selection mechanisms.

Clonal persistence of B lymphocytes in normal mice is determined by variable region-dependent selection

Many adult splenic B cells die within 1 week in the spleen of adoptive adult recipient mice; in contrast, the cellular environment of newborn recipients allows for their expansion and persistence for several weeks. In the present study, we show that the local environment of adult peritoneal cavity also allows adult splenic B cells to persist for over 2 weeks after intraperitoneal transfer. In order to determine whether the persistence of donor B cells in newborn hosts and in the peritoneum of adult recipients results from a selection process involving the clonal specificities expressed, the variation in time of VH gene family repertoires of donor B cells was analyzed in the hosts. At different times after the transfer of splenic cells from lipopolysaccharide (LPS)-reactive mice into LPS-non responder histocompatible recipients, mRNA colony blot assays were performed. The results show that among the donor adult LPS-reactive B cells, the VH genes are differently used by the expanding or persisting B cells, in both kinds of recipients. Thus, cells expressing J558 or VH11 gene families are, in particular, positively selected, while those expressing D-proximal or J606 and 36-30 VH gene families are less selected. These findings demonstrate that the propensity of B cells to persist and expand is determined by their selection through their immunoglobulin variable regions, rather than by genetic properties linked to particular B cell subsets.

Most peripheral B cells in mice are ligand selected

Using amplified cDNA and genomic libraries, we have analyzed the VH gene repertoire of pre-B cells and various B cell subsets of conventional mice at the level of VH genes belonging to the J558 VH gene family. The sequence data were evaluated on the basis of a newly established list of 67 J558 VH genes that comprise approximately two-thirds of the J558 VH genes of the murine IgHb haplotype. The results of the analysis demonstrate that VH gene utilization in pre-B cells, although biased to some extent by B cell autonomous VH gene selection, scatters over the whole range of J558 VH genes present in the germline. In contrast, in mature, peripheral B cells comprising long-lived mu + delta high B cells as well as Ly-1 B cells, small overlapping sets of germline VH genes are dominantly expressed. The data indicate that the recruitment of newly generated B cells into the long-lived peripheral B cell pool is mediated through positive selection by internal and/or external antigens. Because of the absence of immunoglobulin class switching and somatic hypermutation, this process is different from the selection of memory B cells in T cell-dependent immune responses.

Antibody specificity and immunoglobulin VH gene utilization of human monoclonal CD5+ B cell lines

Human B lymphocytes that bear the CD5 antigen are relatively abundant in early ontogeny and comprise a small fraction of the B cell population in adults. The CD5 B cell subset has attracted much attention because of its possible involvement in autoimmune disease and certain B cell malignancies. To begin to understand the role of CD5 B cells in disease processes, we have generated a panel of ten human monoclonal B cell lines selected for expression of the CD5 antigen. These cell lines were obtained by Epstein-Barr virus transformation of B lymphocytes isolated from the spleen, liver and bone marrow of a 19-week-old fetus, from cord blood and from peripheral blood of healthy volunteers. In addition, one cell line was isolated from the spleen of a patient with chronic lymphocytic leukemia. Here, we describe the antibody and immunoglobulin VH gene repertoire of this panel of CD5 B cell lines. The results of these experiments show that (a) some but not all CD5 B cell lines secrete polyreactive antibodies that bind to a variety of self- and xenoantigens and (b) members of the small VH4, VH5 and VH6 gene families are overrepresented in this panel of cell lines. Nucleotide sequence analysis revealed the expression of VH gene elements that have been previously reported in the preimmune B cell repertoire, in CD5 B cell tumors and in polyreactive antibodies.

Contribution of the VH11 gene family to mitogen-responsive B cell repertoire in C57BL/6 mice

The contribution of VH11 gene family to the development of the primary B cell repertoire has been studied by analyzing 1.8 x 10(4) mitogen induced B lymphocyte colonies. The data demonstrate that VH11 family is predominantly expressed among neonatal splenic as well as adult peritoneal B cell colonies, both rich in Ly-1+ B cells. VH11 gene family expression among B splenocytes decreases during ontogeny and VH11 family pairs stochastically with different V kappa families among mitogen-activated neonatal B cell colonies, which are representative of an antigen unselected B cell repertoire. Thus, an increased VH11 expression among peritoneal and neonatal B cells points towards its biased expression among Ly-1+ B lymphocytes. The restricted V gene rearrangements and VH11-V kappa 9 pairing observed among anti-bromelain-treated mouse red blood cells autoantibodies are likely to be an outcome of both intrinsic gene recombination processes per se as well as selection by an autoantigen and/or local selective environmental factors.

Characterization of the interleukin 5-reactive splenic B cell population

The characteristics of the interleukin (IL) 5-reactive splenic B cell population of C57BL/6 nu/nu mice, with respect to IL 5/IL2 reactivity, cell surface phenotype, VH gene family usage, autoreactivity and the structure of the IL5 receptor (IL5R), were analyzed. It was found that 2%-4% of splenic B cells express relatively high levels of IL 5R as determined by the binding of the anti-IL 5R monoclonal antibody R52.120. Over 90% of the splenic B cells that mature to IgM secretion upon activation with IL5 are comprised in this small subpopulation of B cells. Moreover, the vast majority of splenic B cells that mature to IgM-secreting cells when activated by IL2 also reside in this IL5R+B cell population. The cell surface phenotype of the IL5R+ splenic B cells is IgM+, B220+, Ly-1- and IL2R p55-. Upon activation with IL5 this cell surface phenotype changes, in that a vast majority of the B cells then express the p55 chain of the IL2R, whereas the level of IL5R decreases. VH gene family usage in the IL5-activated splenic B cells was analyzed by in situ hybridization. VH gene family usage was found to be random and not different from the VH genes expressed in LPS-activated B cells. Hybridoma collections from IL5-activated splenic B cells and LPS-activated B cells were screened and compared for the production of autoantibodies and antibodies directed against the haptens (4-hydroxy-3-iodo-5-nitrophenyl)acetyl (NIP) and 2,4,6-trinitrophenyl (TNP). In both collections high, but not significantly different frequencies of autoantibody-(32% IL5, 31.4% LPS) and of anti-hapten antibody (27.8% IL5, 18.6% LPS)-producing hybridomas were found. The structure of the IL5R on IL5-activated B cells was analyzed by 125I-labeled IL5 binding and cross-linking. About 100 high-affinity (10(-11) M) and 1000 low-affinity (10(-9) M) IL5-binding sites are present on IL5-activated splenic B cells, and both high- and low-affinity IL5R are similar to those expressed on the IL5-dependent B13 cell line. Cross-linking of 125I-labeled IL5 to the receptors on IL5-activated B cells revealed one major IL5-binding protein of 45-50 kDa molecular mass and another minor binding protein of 130-140 kDa. The same IL5-binding proteins are present on the IL5-dependent B13 cell line.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoglobulin VH gene expression following hemorrhage

Hemorrhage has multiple effects on immunologic response, including alteration of B cell repertoires. In limiting dilution studies, decreased absolute frequencies of splenic clonal precursors specific for bacterial antigens were found after blood loss. In order to better define the effects of hemorrhage on B cell function, we examined immunoglobulin VH gene family expression following blood loss using both in situ hybridization and the RNA colony blot technique. No changes in VH gene family utilization were found after hemorrhage. These results demonstrate that the hemorrhage induced alteration in B cell function involves all VH gene families, without modifying distributive frequencies in VH gene family expression.

All VH11 genes expressed in peritoneal lymphocytes encode anti-bromelain-treated mouse red blood cell autoantibodies but other VH gene families contribute to this specificity

We have studied the relationship between B cell reactivity to bromelain-treated autologous mouse erythrocytes (BrMRBC) and expression of the VH11 gene family in splenic, peritoneal and pleuropericardial cell populations from normal C57BL/6 mice. B lymphocytes producing antibodies to BrMRBC were selectively enriched or depleted from normal populations by rosette formation with BrMRBC, followed by centrifugation over density gradients. This selection method, based on the presence of functional receptors (membrane IgM), is harmless for the cells and allowed subsequent cloning in agar (colony-forming unit-B). The utilization of the 10 VH gene families was then scored in mRNA colony blot assays. The analysis of greater than 650 anti-BrMRBC clones and greater than 350 VH11-expressing colonies indicates that about half of those antibody reactivities are encoded by VH11 genes. Furthermore, it appears that all VH11-expressing B cells in the peritoneal cavity produce anti-BrMRBC antibodies.

VH gene family repertoires of "viable motheaten" (mev) mice

Mutant viable motheaten (mev) mice provide an useful experimental model to study the origin and molecular properties of autoantibodies. In the present investigation we have compared by in situ hybridization VH gene family usage in lipopolysaccharide-activated B cells (available repertoire) and spontaneously immunoglobulin-secreting (actual repertoire) B cells in the spleen of 6-8-week-old BALB/c and mutant BALB/c-mev mice. We have found that while sharing identical available splenic repertoires and expressing a diversified set of VH families, mev mice differ from control BALB/c animals in VH family representation in the actual plasma cell repertoires where they showed a decreased utilization of VH7183 genes and an increased representation of the VHJ606 family when compared to control BALB/c animals. These results indicate that selection of actual repertoires may indeed differ between autoimmune and control mice, but do not establish whether such changes are the primary cause of the disease or whether they are secondary to the initiating of the autoimmune process.

Variable region sequences of pathogenic anti-mouse red blood cell autoantibodies from autoimmune NZB mice

New Zealand Black (NZB) mice spontaneously develop a severe autoimmune hemolytic anemia due to the production of anti-mouse red blood cell (MRBC) autoantibodies. The contribution of variable region genes and somatic mutations in the pathogenicity of anti-MRBC autoantibodies was investigated by mRNA sequencing of eight NZB anti-MRBC monoclonal autoantibodies, among which five are capable of inducing anemia in BALB/c mice. Here we report that at least three VH gene families (J558, J606 and 3609) and five Vchi subgroups (V chi 8, 9, 19, 21 and 28), in combination with several D, JH and Jchi gene segments, encode anti-MRBC autoantibodies. Thus, the NZB anti-MRBC autoantibodies, whether pathogenic or not, are encoded by a large number of immunoglobulin gene elements and by members of known VH and Vchi gene families with preferential usage of VH gene families most distal to the D regions. The presence of several mutations in the JH gene segments of both IgM and IgG anti-MRBC autoantibodies, whether pathogenic or not, strongly suggests that their VH regions may be highly mutated and that the mechanism of somatic diversification might be important in the generation of anti-MRBC autoantibodies. Our results support the idea that anti-MRBC autoimmune responses are likely to be generated by an antigen-driven mechanism.

The peritoneal Ly-1 (CD5) B cell repertoire is unique among murine B cell repertoires

Ly-1 (CD5) B cells and conventional B cells represent two distinct lineages of murine B cells which are distinguishable by expression of surface molecules, organ location, ontogeny and development and antibody production in vivo. In order to assess whether the different developmental pathways of Ly-1 B cells and conventional B cells result in different antibody repertoires, we have used limiting dilution analyses to determine frequencies of B cells making antibodies capable of binding to a range of antigens including haptens, proteins, bacterial polysaccharides and bromelain-treated mouse red blood cells. Starting populations of B cells were purified from spleen, peritoneum and bone marrow of adult BALB/c mice or from spleens of newborn mice by use of the fluorescence-activated cell sorter. The peritoneal Ly-1 B cell repertoire was found to be different from that of conventional B cells, with between 5- and 100-fold higher frequencies of clones producing IgM antibodies capable of binding to the antigens tested. However, when tested, the majority of Ly-1 B cell anti-haptenic antibodies did not show the high affinity binding or fine specificity characteristics of specific antibodies elicited in immune responses in vivo. The high frequencies of antigen-reactive antibodies within the Ly-1 B repertoire are most likely explained by the presence of clones secreting low-affinity or multireactive antibodies. The Ly-1 B cell repertoire is not mirrored in repertoires from either newborn B cells or virgin B cells in adult bone marrow. Therefore, either Ly-1 B cells develop from distinct precursors with intrinsically different mechanisms of V gene usage and recombination, or newly formed Ly-1 B are heavily selected on specificity for entry into this peritoneal lineage. If the second alternative is true, bacterial antigens in the gut are not required for selection of this unique repertoire, as Ly-1 B cells in germ-free mice also show the multireactive repertoire characteristic of this B cell lineage in normal mice.

Organization of the Ig VH locus in mice and humans

In order to assess the contribution of the germline VH gene repertoire to antibody diversity, many groups have studied the evolution and the organization of the immunoglobulin VH gene locus in mice and humans. Here, Ulrich Krawinkel, Thomas Christoph and Thomas Blankenstein review recent data on this subject and discuss the potential influence of gene organization on the activation of the VH gene repertoire during the development of the mammalian immune system.