Early human IgH gene assembly in Epstein-Barr virus-transformed fetal B cell lines. Preferential utilization of the most JH-proximal D segment (DQ52) and two unusual VH-related rearrangements

Survival of the fetus: fetal B and T cell receptor repertoire development

A mature and diverse T and B cell receptor repertoire is a prerequisite for immunocompetence. In light of its increased susceptibility to infection, the human fetus has long been considered deficient in this regard. However, data accumulated since the 1990s and in earnest in the past couple of years paints a more complicated picture. As we describe in this review, mechanisms responsible for generating a diverse receptor repertoire, such as somatic recombination, class switch recombination, and somatic hypermutation, are all operational to surprising extents in the growing fetus. The composition of the fetal repertoire differs from that of adults, with preferential usage of certain variable (V), diversity (D), and joining (J) gene segments and a shorter complementarity determining (CDR3) region, primarily due to decreased terminal deoxynucleotidyl transferase (TdT) expression. Both T and B cell receptor repertoires are extremely diverse by the end of the second trimester, and in the case of T cells, are capable of responding to an invading pathogen with in utero clonal expansion. Thus, it would appear as though the T and B cell receptor repertoires are not a hindrance towards immunocompetence of the newborn. Our improved understanding of fetal receptor repertoire development is already bearing fruit in the early diagnosis of primary immunodeficiencies (PID) and may help clarify the pathogenesis of congenital infections, recurrent abortions, and autoimmune disorders in the near future.

Soma-to-germline feedback is implied by the extreme polymorphism at IGHV relative to MHC: The manifest polymorphism of the MHC appears greatly exceeded at Immunoglobulin loci, suggesting antigen-selected somatic V mutants penetrate Weismann's Barrier

Soma-to-germline feedback is forbidden under the neo-Darwinian paradigm. Nevertheless, there is a growing realization it occurs frequently in immunoglobulin (Ig) variable (V) region genes. This is a surprising development. It arises from a most unlikely source in light of the exposure of co-author EJS to the haplotype data of RL Dawkins and others on the polymorphism of the Major Histocompatibility Complex, which is generally assumed to be the most polymorphic region in the genome (spanning ∼4 Mb). The comparison between the magnitude of MHC polymorphism with estimates for the human heavy chain immunoglobulin V locus (spanning ∼1 Mb), suggests IGHV could be many orders of magnitude more polymorphic than the MHC. This conclusion needs airing in the literature as it implies generational churn and soma-to-germline gene feedback. Pedigree-based experimental strategies to resolve the IGHV issue are outlined.

Activation of V(D)J recombination at the IgH chain JH locus occurs within a 6-kilobase chromatin domain and is associated with nucleosomal remodeling

IgH genes are assembled during early B cell development by a series of regulated DNA recombination reactions in which DH and JH segments are first joined followed by V(H) to DJH rearrangement. Recent studies have highlighted the role of chromatin structure in the control of V(D)J recombination. In this study, we show that, in murine pro-B cell precursors, the JH segments are located within a 6-kb DNase I-sensitive chromatin domain containing acetylated histones H3 and H4, which is delimited 5' by the DQ52 promoter element and 3' by the intronic enhancer. Within this domain, the JH segments are covered by phased nucleosomes. High-resolution mapping of nucleosomes reveals that, in pro-B cells, unlike recombination refractory nonlymphoid cells, the recombination signal sequences flanking the four JH segments are located in regions of enhanced micrococcal nuclease and restriction enzyme accessibility, corresponding to either nucleosome-free regions or DNA rendered accessible within a nucleosome. These results support the idea that nucleosome remodeling provides an additional level of control in the regulation of Ig locus accessibility to recombination factors in B cell precursors.

Developmental changes in the human heavy chain CDR3

The CDR3 of the Ig H chain (CDR3(H)) is significantly different in fetal and adult repertoires. To understand the mechanisms involved in the developmental changes in the CDR3(H) of Ig H chains, sets of nonproductive V(H)DJ(H) rearrangements obtained from fetal, full-term neonates and adult single B cells were analyzed and compared with the corresponding productive repertoires. Analysis of the nonproductive repertoires was particularly informative in assessing developmental changes in the molecular mechanisms of V(H)DJ(H) recombination because these rearrangements did not encode a protein and therefore their distribution was not affected by selection. Although a number of differences were noted, the major reasons that fetal B cells expressed Ig H chains with shorter CDR3(H) were both diminished TdT activity in the DJ(H) junction and the preferential use of the short J(H) proximal D segment D7-27. The enhanced usage of D7-27 by fetal B cells appeared to relate to its position in the locus rather than its short length. The CDR3(H) progressively acquired a more adult phenotype during ontogeny. In fetal B cells, there was decreased recurrent DJ(H) rearrangements before V(H)-DJ(H) rearrangement and increased usage of junctional microhomologies both of which also converted to the adult pattern during ontogeny. Overall, these results indicate that the decreased length and complexity of the CDR3(H) of fetal B cells primarily reflect limited enzymatic modifications of the joins as well as a tendency to use proximal D and J(H) segments during DJ(H) rearrangements.

B-cell precursors differentiated from cord blood CD34+ cells are more immature than those derived from granulocyte colony-stimulating factor-mobilized peripheral blood CD34+ cells

Umbilical cord blood (CB) has been widely used instead of bone marrow (BM) and peripheral blood (PB) for stem cell transplantation (SCT). However, problems of sustained immunodeficiency after CB transplantation remain to be resolved. To elucidate the mechanism of immunodeficiency, we compared the characteristics of B cells differentiated in vitro from CD34+ cells of CB with those of PB. Purified CD34+ cells from CB and PB were cultured on murine stroma cell-line MS-5 with stem cell factor and granulocyte colony-stimulating factor for 6 weeks. The B-cell precursors (pre-B cells) that differentiated in this culture system, were analysed as to their immunoglobulin heavy chain (IgH) variable region gene repertoire and the expression of B-cell differentiation-related genes. CD10+ CD19+ pre-B cells were differentiated from both PB and CB. Although the usages of IgH gene segments in pre-B cells differentiated from CB and PB were similar, the N region was significantly shorter in CB-derived than PB-derived cells. Productive rearrangements were significantly fewer in cells of CB than PB in the third week. Among a number of B-cell differentiation-related genes, the terminal deoxynucleotidyl transferase (TdT) gene was not expressed in CB-derived cells during the culture. These results indicated that immature features of pre-B cells from CB, such as lack of TdT expression, and a short N region and few productive rearrangements in the IgH gene, might cause the delay in mature B-cell production.

Immunoglobulin variable region structure and B-cell malignancies

The enormous diversity of immunoglobulin (Ig) variable (V) gene sequences encoding the antibody repertoire are formed by the somatic recombination of relatively few genetic elements. In B-lineage malignancies, Ig gene rearrangements have been widely used for determining clonality and cell origin. The recent development of rapid cloning and sequencing techniques has resulted in a substantial accumulation of IgV region sequences at various stages of B-cell development and has revealed stage-specific trends in the use of V, diversity, joining genes, the degree of noncoding nucleotide addition, and the rate of somatic mutations. Furthermore, sequences from B-lineage malignant cells nearly reflect the characteristics of the normal counterpart at each respective stage of development. Alternatively, from the IgV region structure of the malignant cells, it is possible to speculate at which stage of B-cell development the cells were transformed. As the complete nucleotide sequences of the human Ig heavy and Ig light V region loci have now been determined, the study of Ig genetics has entered into the super-information era.

Altered VH6-D-JH repertoire in human insulin-dependent diabetes mellitus and autoimmune idiopathic thrombocytopenic purpura

We have characterized the peripheral B cell repertoire in T cell-mediated insulin-dependent diabetes mellitus (IDMM) and in B cell-mediated autoimmune idiopathic thrombocytopenic purpura (AITP). The VH6-containing repertoire in adult patients with IDDM or AITP and healthy control subjects was investigated by PCR amplification using VH6- and JH-specific primers. Nucleotide sequence analysis of VH6-D-JH rearrangements showed an abnormally high frequency of somatic mutations in non-functional rearrangements from diabetic (3. 58 %) as well as AITP patients (3.18 %), compared to controls (0.4 % and 1.43 %, respectively; p < 0.05). In contrast, the mutation frequency among functional rearrangements was 2.4 - 3 times lower in patients compared to controls ( p < 0.05). Detailed analysis of the VH6 genes carrying mutations showed that the underlying mechanism for this observation is probably different for the two diseases. Analysis of D- and JH gene usage revealed additional deviations from the normal pattern. Taken together, these results suggest defects in the mechanisms controlling selection of the B cell repertoire in patients with IDDM or AITP.

Self-reactive antibodies (natural autoantibodies) in healthy individuals

Antibodies that are present in the serum of healthy individuals in the absence of deliberate immunization with any antigen, are refered to as natural antibodies. A vast majority of natural antibodies react with one or more self antigens and are termed as natural autoantibodies. The importance of natural autoantibodies in immune regulation has long been neglected, since tolerance to self was thought to be primarily dependent on the deletion of autoreactive clones, rather than on peripheral suppressive mechanisms. Clonal deletion and energy cannot account, however, for the prevalence of natural autoreactivity among healthy individuals. It is now well established that autoreactive antibodies and B cells, and autoreactive T cells, are present in healthy individuals, and in virtually all vertebrate species. Autoreactive repertoires are predominantly selected early in ontogeny. Questions pertaining to the role of natural antibodies in the regulation of the immune response and maintenance of immune homeostasis and to the distinction between natural autoreactivity and pathological autoimmunity have not been adequately addressed. Here, we focus on the current knowledge on the physicochemical and functional properties of NAA in man, and the use of NAA for therapeutic intervention. reserved.

Immunoglobulin heavy chain junctional diversity in young and aged humans

The causes of observed deficiencies to the humoral immune response in aged humans are unknown. Since a major source of antibody diversity is generated at the VH-D-JH junctional regions of the immunoglobulin heavy chain, we determined whether differences in junctional diversity are manifested with aging. We compared the CDR3 regions of IgM heavy chain transcripts isolated from young adult and aged humans. A PCR assay that measures CDR3 length in the majority of mu-heavy chains showed the same average size and normal range of CDR3 length in aged individuals as observed in young adults. To characterize the features of junctional diversity of aged adults in more detail, we determined the CDR3 sequences of a subset of the mu-heavy chain repertoire that utilizes members of the VH 5 family. In general CDR3 length, D family usage, and JH gene usage were similar in aged compared to young adults. Thus, in contrast to dramatic changes in heavy chain junctional diversity associated with fetal to adult development, no major differences were found between young and aged adults. Since the CDR3 repertoire generated in aged individuals appears to be as diverse as that observed in younger adults, the decline in humoral immunocompetence with aging cannot be attributed to a restriction in heavy chain junctional diversification processes.

Population and family studies of three disease-related polymorphic genes in systemic lupus erythematosus

The contribution to systemic lupus erythematosus (SLE) of three lupus-associated polymorphisms (involving the C4A2 complement component, Humhv3005 and the T cell antigen receptor alpha chain gene) are investigated in 81 individuals from 14 multiplex SLE families, 41 unrelated lupus patients, and 88 unrelated healthy controls. The results show a strong association between C4A deletion and SLE in these families. While the current study confirms the previously reported association between hv3005 deletion and sporadic SLE, the study fails to support this association in familial SLE patients. Moreover, no correlation is detected between the occurrence of hv3005 deletion and C4A null alleles in lupus patients, suggesting that the effects of these genetic polymorphisms on predisposition to lupus are independent. The previously reported lupus-associated T cell receptor (TCR) alpha chain polymorphism is not detected in any of the individuals studied here. The combined data suggest that C4A null alleles predispose strongly to development of lupus, whereas the influence of hv3005 deletion is relatively weak. The results also suggest that contributions of weak susceptibility genes such as hv3005 to disease predisposition may be obscured by the effects of stronger genetic factors and thus need to be examined in patients lacking these factors.

A second promoter and enhancer element within the immunoglobulin heavy chain locus

The joining of immunoglobulin gene segments during B cell development consists of a tightly regulated series of rearrangement steps. A variety of experiments have suggested that transcription is involved in activating the locus as substrate for the V(D)J recombinase. Here, we have characterized a region located immediately upstream of the most J-proximal D element (DQ52), which contains both promoter and enhancer activities preferentially active in precursors of B cells. Interestingly, this DQ52 regulatory element is inevitably deleted in fully rearranged H chain genes. We propose that it is involved in the early activation and rearrangement events at the IgH locus.

B precursor acute lymphoblastic leukemia third complementarity-determining regions predominantly represent an unbiased recombination repertoire: leukemic transformation frequently occurs in fetal life

To determine whether the ALL (acute lymphoblastic leukemia) CDR3 (third complementarity-determining region) repertoire represents the recombination repertoire, or shows evidence of selectional processes inherent to normal B cell differentiation or malignant transformation, we analyzed 68 ALL CDR3 regions and included 127 previously published sequences in the analyses. We found no evidence of selection prior to malignant transformation as recombination was random with 1/3 "in frame" and 2/3 "out of frame" joinings and usage of all three D reading frames was observed. D and JH gene segments were predominantly unmutated which allowed a detailed analysis of gene usage and rearrangement characteristics. JH4 and JH6 usage (both 32.2%) was significantly different (p = 0.005) from that observed in peripheral B lymphocytes. D gene family usage roughly represented D gene family size with the exception of the DXP and DA/K family which were over- and underrepresented (p = < or = 0.05), respectively. D-D fusions were found in 26.2% of CDR3 regions. If less stringent criteria were applied DIR homology was found in 40/65 sequences, suggesting the frequent involvement of DIR gene segments in human CDR3 formation. The rearranged D genes were evenly distributed over the D locus, suggesting that D recombination is a predominantly random process, independent of physical location at the locus. Also, there was no correlation between JH gene usge and physical location of the rearranged D gene segment, which excludes a major contribution of the DJH replacement recombination mechanism. In 36.1% of CDR3 regions N-nucleotides at the DJH junction were absent. This frequency is higher than observed for peripheral B lymphocytes. It is suggested that for a number of ALL the initial transformational event took place in early fetal life. We conclude that ALL CDR3 sequences show no evidence of selection prior to malignant transformation, nor of extensive changes subsequent to malignant transformation.

Expansion of a B-lymphocyte clone producing IgM auto-antibodies encoded by a somatically mutated VHI gene in the spleen of an autoimmune patient

Seventy-six human B-cell hybridomas were obtained by fusing B lymphocytes from the spleen of a patient with chronic idiopathic thrombocytopenia (ITP). Two independent hybridoma clones producing IgM autoantibodies reacting with platelets and other antigens from both the internal and the external environments were established from this fusion experiment. The IgM autoantibodies produced by the two hybridoma clones were found to be encoded by identical VHDJH and VLJL genes. The comparison of the VHI gene expressed in both hybridomas with the germline equivalent cloned from the patient's DNA showed two somatic mutations in the complementarity-determining regions CDR1 and CDR2 resulting in amino acid replacements. These data suggest the selection and expansion of an autoantibody-producing B-cell clone in the spleen of an ITP patient, probably as a result of (auto)antigen-driven stimulation.

Immunoglobulin variable region sequences of two human monoclonal antibodies directed to an onco-developmental carbohydrate antigen, lactotetraosylceramide (LcOse4Cer)

A human monoclonal antibody, 11-50, was generated and was shown to recognize an onco-developmental carbohydrate antigen, LcOse4Cer. The isotype of this antibody was IgM, lambda, similar to the previously known human anti-LcOse4 antibodies, such as IgMWOO and HMST-1. We raised a murine anti-idiotypic antibody G3 (IgG1, kappa) against 11-50, and tested its reactivity towards the affinity purified human polyclonal anti-LcOse4 antibodies prepared from pooled human sera using a Gal beta 1-->3GlcNAc beta-immobilized column. The results indicated that at least a part of the human polyclonal anti-LcOse4 antibodies shared the G3 idiotype with 11-50. We further analyzed the sequence of variable regions of the two anti-LcOse4 antibodies, 11-50 and HMST-1. Sequence analysis of the heavy chain variable regions indicated that the VH regions of these two antibodies were highly homologous to each other (93.5% at the nucleic acid level), and these antibodies utilized the germline genes VH1.9III and hv3005f3 as the VH segments, which are closely related germline genes of the VHIII family. It was noted that these germline VH genes are frequently utilized in fetal B cells. The JH region of both antibodies was encoded by the JH4 gene. For the light chain, the V lambda segments of the two antibodies were 96.3% homologous to each other at the nucleic acid level. The V lambda segments of both antibodies showed the highest homology to the rearranged V lambda gene called V lambda II.DS among reported V lambda genes, while the exact germline V lambda genes encoding the two antibodies were not yet registered in available sequence databanks. The amino acid sequences of the J lambda segments of both antibodies were identical. These results indicate that the two human antibodies recognizing the onco-developmental carbohydrate antigen Lc4 are encoded by the same or very homologous germline genes.

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.

Human immunoglobulin heavy-chain minilocus recombination in transgenic mice: gene-segment use in mu and gamma transcripts

We (N.L. and L.D.T.) have introduced a human heavy-chain minilocus into mice transgenically. Constructs contain 2 heavy-chain variable (VH; psi VH3-105 and VH5-251), 10 diversity (D), 6 heavy-chain joining (JH), and either constant (C)mu or C mu and C gamma gene segments. Several founder lines were established and studied before immunization. Seventy heavy-chain transcripts were cloned and sequenced from murine splenic B lymphocytes, and gene-segment use was assessed before and after class-switching. In general, the repertoire was "fetal" in appearance with little evidence of somatic mutation in any gene segment. The two VH gene segments were found rearranged to mu- and gamma-chain C segments, with a preference of VH5-251. We observed a preponderance of the most-J-proximal D gene (DHQ52) segments among the mu transcripts (44%). The JH gene-segment use mimics most patterns seen in human antibodies. Diversification in CDR3 was extensive and included clear examples of D inversions and D-D fusions. These data suggest that a human immunoglobulin minilocus can undergo recombinatorial processes in a manner analogous to that seen in the human fetal/preimmune repertoire. This model, in addition to providing a potential source of human monoclonal antibodies, is ideal for the study of further questions concerning immunoglobulin gene-segment recombination.

Characterization of two human anti-DNA antibodies bearing the pathogenic idiotype 8.12

Antibodies against double stranded DNA (dsDNA) are characteristic of systemic lupus erythematosus (SLE) and have been implicated in disease pathogenesis. Up to one third of an SLE patient's anti-dsDNA antibodies can express the lambda L chain idiotype 8.12. Serum titers of this idiotype are elevated in 50% of SLE patients, and idiotypic antibodies are present in glomerular immune deposits associated with lupus nephritis. Two EBV transformed B cell lines, KS3 from a patient with SLE and SD6 from an individual without autoimmune disease, secrete 8.12+ IgG antibodies that bind dsDNA. The 8.12+ lambda L chains of these anti-DNA antibodies are encoded by members of the V lambda II gene family; the KS3 heavy chain is encoded by a VH4-DM1-DQ52-JH6b-C gamma 1 gene rearrangement and the SD6 heavy chain is encoded by a VH3-D21/9-JH6b-C gamma 1 rearrangement. Both of these monoclonal antibodies are somatically mutated: the KS3 antibody displays mutations in complementarity determining regions (CDRs) and the SD6 antibody in framework regions (FRs). The significance of these different patterns of mutation in two potentially pathogenic anti-DNA antibodies is discussed.

Mechanisms that generate human immunoglobulin diversity operate from the 8th week of gestation in fetal liver

The repertoire of immunoglobulin expressed very early in human development was approached by cloning and sequencing 55 rearranged and 11 germ-line VH transcripts, after amplification by polymerase chain reaction of cDNA libraries derived from two fetal livers at 8 and 13 weeks of gestation. All families with the exception of VH2, were expressed as soon as 8 weeks, with preferential usage of certain germ-line genes. Very few somatic mutations, randomly localized, were identified. By contrast, in a series of clones derived from the same VDJ rearrangement using the VH6 family, extensive mutations had taken place, mostly accumulated in the third complementarity-determining region (CDR3) suggesting that the specialized enzymatic machinery was at hand very early during human development. Some other characteristics of the fetal repertoire also emerged, namely increased usage of JH3 and JH2, as compared to the adult pattern, where JH4 is dominant and reduced length of the D/CDR3 regions. All D gene families were identified, and their usage frequently involved D-D fusions. N diversity was present very early, and increased with age. Identification of germ-line transcripts pertaining to all six VH families including pseudogenes, in the E55 library, revealed a population very different as compared to rearranged gene transcripts. This suggests that a large portion of VH locus is accessible for transcription, bringing no evidence of correlation between preferential rearrangement of a given VH gene and its localization in the locus.

Structure and physical map of 64 variable segments in the 3'0.8-megabase region of the human immunoglobulin heavy-chain locus

We have constructed the physical map of the 0.8 megabase DNA fragment which contains the 3' 64 variable region (V) gene segments of the human immunoglobulin heavy chain (H) locus. The organization of the VH locus showed several features that indicate dynamic reshuffling of this locus. The sequenced 64 VH segments include 31 pseudogenes, of which 24 are highly conserved except for a few point mutations. Comparison of the 64 germline VH sequences shows that each VH family has conserved sequences, suggesting that there might be some genetic or selection mechanisms involved in maintenance of each family. The total number of the human VH segments was estimated to be about 120, including at least 7 orphons.

Thymic selection of the human T cell receptor V beta repertoire in SCID-hu mice

Implantation of pieces of human fetal liver and thymus into SCID mice results in the development of a human thymus-like organ, in which sustained lymphopoiesis is reproducibly observed. In this model, T cell development can be experimentally manipulated. To study the influence of thymic selection on the development of the human T cell repertoire, the T cell receptor (TCR) V beta gene repertoire of double-positive (CD4+CD8+) and single-positive (CD4+CD8- and CD4-CD8+) T cells was analyzed in the SCID-hu thymus using a multiprobe ribonuclease protection assay. TCR diversity in double-positive SCID-hu thymocytes was found to be comparable with that present in the thymus of the fetal liver donor, did not change with time, and was independent of the origin of the thymus donor. Thymic selection in SCID-hu thymus induces changes in V beta usage by the single-positive CD4+ or CD8+ T cells comparable with those previously reported for single-positive cells present in a normal human thymus. Finally, significant differences were observed in the V beta usage by CD4 or CD8 single-positive T cells that matured from genetically identical stem cells in different thymic environments. Collectively, these data suggest: first, that the generation of TCR diversity at the double-positive stage is determined by the genotype of the stem cells; and second, that polymorphic determinants expressed by thymic epithelium measurably influence the V beta repertoire of mature single-positive T cells.

Chromosomal organization of the heavy chain variable region gene segments comprising the human fetal antibody repertoire

The adult repertoire of antibody specificities is acquired in a developmentally programmed fashion that, in mouse and man, parallels the ordered rearrangement of a limited number of germ-line heavy chain variable region (VH) gene segments during development. It has been hypothesized that this developmental bias is a consequence of gene organization. In the mouse, rearrangement of VH gene segments proximal to the heavy chain joining region (JH) locus precedes rearrangement of genes located more distal to the JH locus. Similarly, in man, two VH elements located proximal to JH are expressed during fetal development. To test further this hypothesis in man, we have determined in a single individual the positions of an additional eight distinct VH elements known to comprise a significant fraction of the human developmental repertoire. These developmentally expressed VH elements were found to be dispersed over a region of 890 kilobases of the VH locus and were interspersed with other VH elements that are not known to be developmentally expressed. Thus, the ordered developmental expression of VH gene segments in man must involve mechanisms beyond physical proximity to the JH locus. Further, these results support the notion that fetal expression of VH gene segments is a regulated process and suggest that this regulation is important in the acquisition of immunocompetence.

Cellular proliferation and genetic events involved in the genesis of Burkitt lymphoma (BL) in immune compromised patients

A mathematical model simulating lymphomagenesis based on the two-hit theory of carcinogenesis is presented by contrasting the biologic variables responsible for a high risk of developing Burkitt lymphoma (BL) in three immunosuppressed groups with that of nonendemic BL. In this model, the pro-B lymphocyte is considered to be the target for BL-specific translocations such as t(8;14). With repeated mitosis, the target cell pool expands in the high-risk individual, and, thereby, the opportunities for a spontaneous translocation to arise are increased. The chromosomal translocation endows the target cell with survival advantages, and, hence, lymphoma develops. Modeling results demonstrate that this increased cell proliferation is sufficient in accounting entirely for the increase in tumor prevalence. Preventing enhanced cellular proliferation by obviating immune deficiency and treating patients with agents that restore immunity or have antiviral and antiproliferative properties prior to conversion from polyclonal B-cell proliferation to monoclonal malignancy could obviate the development of BL.

The repertoire of human germline VH sequences reveals about fifty groups of VH segments with different hypervariable loops

We have used the polymerase chain reaction and VH family-based primers to clone and sequence 74 human germline VH segments from a single individual and built a directory to include all known germline sequences. The directory contains 122 VH segments with different nucleotide sequences, 83 of which have open reading frames. The directory indicates that the structural diversity of the germline repertoire for antigen binding is fixed by about 50 groups of VH segments: each group encodes identical hypervariable loops. The directory should help in mapping the VH locus, in estimating somatic mutation and VH segment usage and in designing and constructing synthetic antibody libraries.

A survey of protein-DNA interaction sites within the murine immunoglobulin heavy chain locus reveals a particularly complex pattern around the DQ52 element

The expression of immunoglobulin (Ig) genes is regulated at two levels: rearrangement of individual gene segments and transcription of continuous genes. To find transacting factors involved in mediating locus- and segment specific gene activation and expression, we surveyed a 3600-bp genomic region of the murine Ig heavy chain locus, spanning from the DQ52 element to the Ig heavy chain intron enhancer. We discovered nine, previously undescribed, protein-DNA complexes and estimated their individual binding-affinity preferences (Kr) by quantitative gel shift measurements. We observed one novel protein DNA interaction at the enhancer, two in the JH1 region and six within a 300-bp region immediately 5' to the DQ52 locus. The latter show a complex and specific binding pattern when comparing nuclear extracts derived from pre-B cells and fibroblasts. Further characterization of the interactions at the DQ52 locus by electron microscopy revealed the preferential formation of a protein complex binding to the DQ52 locus with pre B cell extracts. This behavior and the clustering of interaction sites 5' to the DQ52 element suggest that this region is involved in the regulation of heavy chain gene assembly.

Analysis of immunoglobulin variable region genes from human IgG anti-DNA hybridomas

The molecular mechanisms leading to anti-double-stranded (ds) DNA antibody production in systemic lupus erythematosus (SLE) are poorly understood. We describe here the immunoglobulin variable region genes of six human hybridomas secreting IgG anti-dsDNA antibodies derived from three SLE patients. The monoclonal IgG anti-dsDNA antibodies have been shown to be of high affinity and no multireactivity was observed (Winkler et al., Clin. Exp. Immunol., 1991. 85: 379). The comparison of the variable region genes expressed in the hybridomas with known germ-line genes as well as with the germ-line counterparts from one patient shows that the VH and VL sequences are somatically mutated. The pattern and extent of the observed somatic mutations are suggestive for an antigen-driven selection of at least four of these B cell clones. Several VH and VL genes used by the hybridomas were found to be expressed in the natural antibody repertoire, in the restricted fetal repertoire and in B cell malignancies expressing the CD5 antigen.

Germ line transcription of the immunoglobulin heavy chain locus directs production of mu chain without VDJ

Immunoglobulin VDJ recombination is associated with transcriptional activation of the Ig variable region elements. We have previously described a novel Ig mu chain protein and mRNA produced by pre-B cell hybrids from normal and X-linked agammaglobulinemic bone marrow. We have now characterized the mRNA encoding this protein and find that it is composed of a 5' leader sequence spliced to C mu (LS-C mu), lacking the variable (V), diversity (D), and joining (J) gene sequences. The leader sequence is encoded by a novel exon 16 kb upstream of the JH locus. Transcription of the germ line heavy chain locus from this LS exon results in transcriptional activation of the JH locus, apparently the initial step in commitment to B lymphoid development. Polymerase chain reaction amplification of normal bone marrow shows that these germ line LS-C mu transcripts are a product of bone marrow pre-B cells. Production of LS-C mu commences a sequential process of transcriptional activation, with concordant translation of Ig rearrangement intermediates, in the process of creating a productive VDJ rearrangement.

Characterization of the immunoglobulin heavy chain complementarity determining region (CDR)-III sequences from human B cell precursor acute lymphoblastic leukemia cells

Sequence analysis of the immunoglobulin heavy chain complementarity determining region (CDR)-III of B-lineage cells at various stages has provided important insights concerning B cell maturation and selection. Knowledge of human CDR-III sequences has been relatively limited compared with that of the murine system. We analyzed the CDR-III sequences of B cell precursor acute lymphoblastic leukemia (pre-B ALL) cells in 23 newly diagnosed and 10 relapsed patients, in order to elucidate the organization of CDR-III in B cell precursors. We found a very low frequency of somatic mutations in D and JH regions, preferential use of DLR, DXP, DHQ52, and DN elements, and of 3' side JH segments, and no predominant usage of D coding frames. Unusual joinings such as VH-D-D-JH and VH-JH were observed in three, and one sequences, respectively. We compared the CDR-III sequences derived from 10 patients between diagnosis and relapse. Two of them had three spots of mutated nucleotides at relapse, all of which were found in the N region near the D segments. Our data showed the possibility of somatic mutation at relapse, in addition to developmentally regulated rearrangement of the immunoglobulin gene at the stage of B cell precursors.

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.

The human cord blood antibody repertoire. Frequent usage of the VH7 gene family

We have previously demonstrated a consistent preferential usage of a small set of VH, DH and JH gene segments in second-trimester fetal liver. To examine the extent of heavy chain repertoire diversification in newborns, we generated an unrestricted cDNA library from cord blood mononuclear cells and sequenced the variable domains of randomly isolated Cmu+ transcripts. We found this set of transcripts to be enriched for JH4, 5 and 6, whereas previously reported fetal transcripts preferentially expressed JH3 and 4. The cord blood transcripts used a number of different DH gene segments, whereas fetal transcripts were enriched for DHQ52. Of the thirteen cord blood sequenced, three were members of the newly described VH7 family which to date has not been detected in fetal liver. Indeed, only one of the isolated VH gene segments had been previously observed in fetal transcripts. As a result of enhanced N-region addition and use of longer DH and JH gene segments, both the sequence diversity and range of potential antigen-binding structures of cord blood complementarity-determining region 3 domains was vastly expanded. Thus, the repertoire bias evident in fetal liver was no longer apparent in this more mature population of cord blood B cells.

Restricted utilization of germ-line VH3 genes and short diverse third complementarity-determining regions (CDR3) in human fetal B lymphocyte immunoglobulin heavy chain rearrangements

Twenty-one independent immunoglobulin heavy chain VH3DJH rearrangements were cloned and sequenced from livers of human fetuses at 7, 13 and 18 weeks of gestation. The VH elements expressed were not somatically mutated. Eight out of the estimated 30 VH3 elements were utilized with a preference for five of them. One of these VH3 sequences, designated FL13-28, represented a thus-far unknown VH3 gene segment. From the six functional JH elements the JH3 and JH4 segments were utilized preferentially and from the estimated 30 D segments the DQ52 element and the Dxp family were found to rearrange frequently. D elements were utilized both in normal and inverted orientation, as single copies or in D to D fusions. Addition of N nucleotides, removal of nucleotides from the coding sequences and utilization of DIR elements (D genes with irregular recombination signals) further expanded the third complementarity-determining region (CDR3) diversity. One fourth of the fetal CDR3 regions lacked N regions. Due to utilization of DQ52, the relative absence of N regions and extensive exonuclease activity operating on the D elements, the fetal CDR3 regions were significantly shorter than those found in adult B lymphocytes.

Diversity of immunoglobulin heavy chain gene segment rearrangement in B lymphoblastoid cell lines from X-linked agammaglobulinemia patients

X-linked agammaglobulinemia (XLA) is characterized by an arrest in early B lymphocyte differentiation. Precursor B cells are present in the bone marrow (BM), whereas peripheral blood B cell numbers are severely decreased. A series of Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) was established from peripheral blood of three XLA patients belonging to one pedigree. These BLCL manifested productive VHDJH rearrangements and a random utilization of the VH families. The CDR3 regions of the rearrangements varied in length from 12 to 47 nucleotides and included N regions in all cases. The results supported the conclusion that the few B lymphocytes in peripheral blood of XLA patients exhibit all mechanisms that generate immunoglobulin (Ig) heavy (H) chain diversity. However, no evidence for somatic mutation was found. Within the VH3 family 50% of the expressed VH gene segments belonged to a single subgroup and within the VH4 family a preferential utilization of one VH4 gene element was observed. The utilization of H chain joining (HH) elements was biased to JH4 and JH6 and a high percentage of the CDR3 regions was found to be generated by unconventional mechanisms, such as multiple D usage and the fusion of D elements to D segments with irregular recombination recognition signals. These unique features of the recombined and expressed VHDJH regions in XLA may explain the inability of XLA patients to respond to a variety of antigens. Alternatively, they could be secondary to a B lymphocyte maturation defect in XLA.

Complete sequence of the genes encoding the VH and VL regions of low- and high-affinity monoclonal IgM and IgA1 rheumatoid factors produced by CD5+ B cells from a rheumatoid arthritis patient

We have characterized the VH and VL genes of three low-affinity polyreactive and two high-affinity monoreactive IgM and IgA1 rheumatoid factor (RF) mAb generated using circulating CD5+ B cells from a single rheumatoid arthritis patient. We found that four and one RF mAb utilized genes of the VHIV and VHIII families, respectively. The VHIV gene usage by these RF mAb differs from the preferential VHIII, VHI, and, to a lesser extent, VHII gene usage by the IgM with RF activity found in patients with mixed cryoglobulinemia, Waldenstrom's macroglobulinemia, and other monoclonal gammopathies. In addition, in contrast to the preponderant kappa L chain usage by the RF in these patients, a lambda L chain was utilized by all RF mAb from our rheumatoid arthritis patient. Two RF mAbs utilized V lambda I, two V lambda IV, and one V lambda III L chains. The VH genes of the two low-affinity polyreactive IgM RF mAb were in germline configuration. When compared with the deduced amino acid sequence of the putatively corresponding genomic segment, the VH gene of the high-affinity monoreactive IgM RF mAb displayed five amino acid differences, all of which are in the complementarity determining regions (CDR), possibly the result of a process of somatic point mutation and clonal selection driven by Ag. The unavailability of the corresponding genomic VH segment sequences made it impossible to infer whether the VH genes utilized by the two IgA1 RF were in a germline or somatically mutated configuration. Sequencing of the genes encoding the H chain CDR3 (D segments) revealed that all three low-affinity polyreactive RF mAb displayed a much longer D segment (36-45 bases) than their high-affinity monoreactive counterparts (15-24 bases), raising the possibility that a long D segment may be one of the factors involved in antibody polyreactivity.

A deletion map of the human immunoglobulin heavy chain variable region

Analysis of VH gene segments deleted in the process of immunoglobulin heavy chain (IGH) variable region assembly in three series of monoclonal B cell lines has been used to determine the human VH region organization. A deletion map of the relative positions of 21 different VH gene segments has been determined. The characterization of B cell lines from three unrelated adults of two racial groups yielded the same relative VH gene segment order, suggesting that the overall order of VH genes in the normal population is constant. This VH gene segment order was consistent with what we had previously generated from physical mapping techniques. DH segments from the second DH cluster, distinct from the major DH locus 3' of the VH region, were not observed to be used in 32 different rearrangements. Approximately 77% of the VH-(D)JH rearrangements involved VH gene segments within 500 kb of the JH region, indicating that human B cell lines preferentially rearrange JH-proximal VH gene segments. The switch, observed in mice, from the fetal use of JH-proximal VH gene segments to an adult VH use dependent upon VH family size may therefore not occur in humans. This detailed map of the VH gene segments is a necessary prerequisite for understanding VH usage in development and disease.

Characterization of human lymphocytes separated from fetal liver and spleen at different stages of ontogeny

Membrane markers on human lymphocytes separated from fetal liver and spleen were studied. Depending on the period of intrauterine development, a growing percentage of T- and B-lymphocytes (up to 16% and 45%, respectively) among spleen cells was seen, but in liver the number was low independent of the gestational age (T cells less than 10% and B cells less than 15%). The majority of early CD3+ spleen cells (21st-28th week) expressed TCR alpha beta but not TCR gamma delta, although a significant proportion of these cells was still lacking CD4, CD8, and CD5 differentiation antigens, suggesting their immaturity. Later spleen T cells (29th-36th week) expressed the phenotype as mature adult-type T cells (CD3+TCR alpha beta +CD4/8+CD5+). During ontogeny in fetal spleen, a growing number of B cells could be estimated without any changes in the proportion of subsets, expressing the different light and heavy chains. However, the proportion of CD5+ B cells decreased with gestational age. The results suggest that the functional immaturity of antenatal splenocytes could not be caused by dramatic phenotypical differences in comparison with adult-type splenic lymphocytes.

Structure and expression of human germline VH transcripts

The human VH5 family consists of two functional genes and one pseudogene. We have found a novel 1.2-kb VH5 gene transcript in normal fetal liver and cord blood and in transformed B lineage cells. VH5-positive cDNA clones were isolated from precursor B acute lymphoblastic leukemia, B chronic lymphoblastic leukemia, Epstein-Barr Virus-transformed B cell lines, and cord blood, and were identified as transcripts of unrearranged VH5 genes (germline transcripts). The cDNA clones were derived from both functional and pseudo-VH5 genes. Most germline transcripts appear to initiate at the normal VH promoter and are cleaved and polyadenylated at sites several hundred bases downstream of the VH5 coding region. Correct splicing of the leader intron was observed in all clones. In functional and pseudo-VH5 cDNAs, an open translational reading frame extends from the leader to a termination codon in the nonamer. Only limited polymorphisms were observed in the coding as well as flanking regions of the VH5 transcripts. Functional and pseudo-VH5 transcripts and previously identified murine germline VHJ558 transcripts are discussed.

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.

Coordination of immunoglobulin DJH transcription and D-to-JH rearrangement by promoter-enhancer approximation

The genes that encode the variable regions of immunoglobulin (Ig) heavy chains are encoded by three DNA segments: VH, D, and JH. During B-cell development these segments are brought together by a pair of site-specific DNA rearrangements. The first of these joins a D segment to a JH segment; the second brings a VH segment in apposition to a DJH unit. B-cell precursors that have undergone D-to-JH joining express transcripts that initiate at the 5' flanks of rearranged D segments (DJH transcription). In this study we have examined the coordination of D-to-JH rearrangement and DJH transcription. The B-lymphoid progenitor cell line HAFTL-1 cell clone, joining of distal D segments (DSP2 and DFL16) to JH is accompanied by an increase in the steady-state level of transcripts initiating 5' of the D coding region. Steady-state transcription of a DSP2 gene segment was undetectable prior to rearrangement and was observed to increase at least 20-fold upon joining to JH. In contrast, transcription from the 5' flank of DQ52, which lies within 700 bp of the JH cluster, was detected prior to rearrangement and did not increase significantly after rearrangement. The 5' flank of a DSP2 segment was found to support expression of a heterologous gene upon transfection into B progenitor cell lines. Expression from this DSP2 promoter was at least 30-fold higher in the presence of the Ig heavy-chain enhancer, in either orientation, than in its absence. A DNA fragment spanning the interval from -165 to +19 bp relative to the major DSP2 transcriptional start site retained enhancer-dependent promoter activity. These observations imply that activation of DSP12JH and DFL16JH transcription is coordinated with D-to-JH rearrangement by approximation of enhancer-dependent D promoter elements to the Ig heavy-chain enhancer. This interpretation is consistent with our observation that the DQ52 segment, which is closely linked to the JH cluster, is transcribed both before and after rearrangement.

Coordination of immunoglobulin DJH transcription and D-to-JH rearrangement by promoter-enhancer approximation

The genes that encode the variable regions of immunoglobulin (Ig) heavy chains are encoded by three DNA segments: VH, D, and JH. During B-cell development these segments are brought together by a pair of site-specific DNA rearrangements. The first of these joins a D segment to a JH segment; the second brings a VH segment in apposition to a DJH unit. B-cell precursors that have undergone D-to-JH joining express transcripts that initiate at the 5' flanks of rearranged D segments (DJH transcription). In this study we have examined the coordination of D-to-JH rearrangement and DJH transcription. The B-lymphoid progenitor cell line HAFTL-1 cell clone, joining of distal D segments (DSP2 and DFL16) to JH is accompanied by an increase in the steady-state level of transcripts initiating 5' of the D coding region. Steady-state transcription of a DSP2 gene segment was undetectable prior to rearrangement and was observed to increase at least 20-fold upon joining to JH. In contrast, transcription from the 5' flank of DQ52, which lies within 700 bp of the JH cluster, was detected prior to rearrangement and did not increase significantly after rearrangement. The 5' flank of a DSP2 segment was found to support expression of a heterologous gene upon transfection into B progenitor cell lines. Expression from this DSP2 promoter was at least 30-fold higher in the presence of the Ig heavy-chain enhancer, in either orientation, than in its absence. A DNA fragment spanning the interval from -165 to +19 bp relative to the major DSP2 transcriptional start site retained enhancer-dependent promoter activity. These observations imply that activation of DSP12JH and DFL16JH transcription is coordinated with D-to-JH rearrangement by approximation of enhancer-dependent D promoter elements to the Ig heavy-chain enhancer. This interpretation is consistent with our observation that the DQ52 segment, which is closely linked to the JH cluster, is transcribed both before and after rearrangement.

Lack of N regions in fetal and neonatal mouse immunoglobulin V-D-J junctional sequences

Much of T and B lymphocyte receptor diversity derives from the addition of nontemplated N regions at the junctions of receptor gene elements, although fetal T cells expressing gamma/delta receptors lack N regions. I have sequenced immunoglobulin H chain variable regions of PCR-amplified DNA and cDNA from fetal and newborn mouse liver and spleen cells. These sequences showed an absence of N regions. Only 1/87 DNA sequences and 17/146 RNA sequences contained N regions, in striking contrast to adult Ig sequences. These data show that N region insertion is a developmentally regulated process in B cells as well as in T cells, and demonstrate that receptor diversity in neonatal B cells is limited by the absence of N regions as well as by biased usage of Vh genes.

Immunoglobulin heavy chain variable region family usage is independent of tumor cell phenotype in human B lineage leukemias

During B cell development, immunoglobulin heavy chain (IgH) variable region (VH) genes are rearranged and expressed in a programmed manner and accumulating evidence suggests recurrent utilization of developmentally restricted VH genes in malignant B lymphoid populations. We have used polymerase chain reaction gene amplification in conjunction with a panel of VH family-specific amplimers to directly compare the repertoire of VH region rearrangement in mature, CD5+ B cell chronic lymphocytic leukemia with that in immature, CD5 B lineage acute lymphoblastic leukemia. The results revealed a diverse pattern of VH family utilization common to both disease groups in which VH regions most proximal to the IgH joining locus were preferentially rearranged relative to their family sizes with recurrent utilization of several known developmentally restricted VH genes in close to germ-line configuration. These results indicate that biased VH family usage is independent of tumor cell phenotype in B lineage leukemias. This bias may reflect similar stages or compartments in normal B lymphopoiesis from which diverse types of B cell malignancy may arise. Moreover, since blast cells in acute lymphoblastic leukaemia do not express functional immunoglobulin, we infer that the tumor cell-associated VH family repertoire is determined through antigen-independent mechanisms.

The complete nucleotide sequences of the heavy chain variable regions of six monospecific rheumatoid factors derived from Epstein-Barr virus-transformed B cells isolated from the synovial tissue of patients with rheumatoid arthritis. Further evidence that some autoantibodies are unmutated copies of germ line genes

Structural studies of human monoclonal rheumatoid factors (RF) derived from patients with monoclonal gammapathies have revealed a restriction in the usage of heavy and light chain variable regions. These studies have suggested that germline genes with little if any somatic mutation can generate RF specificity. However, there is no information presently available regarding the primary structure and genetic origin of RF in rheumatoid arthritis. In this study, we have isolated and sequenced the VH regions of six monoclonal RF derived from the synovial membranes of two patients with rheumatoid arthritis and one with the juvenile polyarticular form of the disease. We found the same VH families as previously reported among monoclonal paraproteins with RF activity. However, our sample was diverse regarding the VH, DH, and JH gene segments used. Among VHI RF there was conservation in the length of CDRIII as well as restriction in the amino acid generated at the V-D junction, as opposed to VHIII RF and non-RF VHI molecules that are highly heterogeneous in these two aspects. We also found that different JH gene segments may contribute to RF specificity. The VH, DH, and JH elements of one RF in our study all had clearly identifiable germline counterparts. This RF displays a nearly germline configuration throughout its entire heavy chain and represents another example of an autoantibody encoded by one of the VH gene segments from the preimmune fetal repertoire.

Human immunoglobulin VH and VK repertoire revealed by in situ hybridization

We report in this paper the first analysis of the expression pattern of Ig VH and VK families in human adult normal peripheral B lymphocytes, by in situ hybridization using specific VH1 to VH6 and VK1 to VK4 probes, which cover the known human V gene families reported to date. The major families were VH3 and VK1, with the respective gradient VH3 greater than VH4 greater than VH1 greater than VH5 greater than VH6 greater than VH2, and VK1 greater than VK3 greater than VK4 greater than VK2. Using a large sampling of EBV clones, we found that the pattern of VH and VK family usage was similar. The expression level correlated fairly with the estimated gene number for the VH, but diverged noticeably for the K chains. Taken together with the fact that the level of light chain expression (K + lambda) was about two-fold that of heavy chains, these results suggest that the VH and the VK repertoires are not regulated by a similar selective process.

Preferential utilization of conserved immunoglobulin heavy chain variable gene segments during human fetal life

The ability to respond to specific antigens develops in a programmed fashion. Although the antibody repertoire in adults is presumably generated by stochastic combinatorial joining of rearranged heavy variable, diversity, and joining (VH-DH-JH) and light (VL-JL) chains, experimental evidence in the mouse has shown nonrandom utilization of variable gene segments during ontogeny and in response to specific antigens. In this study, we have performed sequence analysis of 104-day human fetal liver-derived, randomly isolated constant region C+ mu transcripts and demonstrate a consistent preference during fetal life for a small subset of three highly conserved VH3 family gene segments. In addition, the data show that this preferential gene segment utilization extends to the DHQ52 and the JH3 and JH4 loci. Sequence analysis of two "sterile" DH-JH transcripts suggests that transcriptional activation of the JH-proximal DHQ52 element may precede initiation of DH-JH rearrangement and influence fetal DH utilization. Sequence comparisons reveal striking nucleotide polymorphism in allelic gene segments which is poorly reflected in the peptide sequence, implying considerable evolutionary selection pressure. Although vertebrate species utilize a variety of strategies to generate their antibody repertoire, preferential utilization of VH3 elements is consistently found during early development. These data support the hypothesis that VH3 gene segments play an essential role in the development of the immune response.

Production and regulation of interleukin 6 in human B lymphoid cells

Human B cell lines were screened for production of interleukin 6 (IL 6) by the B9 hybridoma cell bioassay. Some long-established lines such as RPMI 1788, CESS and recently established early-passage Epstein-Barr virus (EBV)-transformed lymphoblastoid lines were constitutive IL 6 producers. Other long-established lymphoblastoid lines such as RPMI 8866 and SKW6.4 and all Burkitt lymphoma lines tested were nonproducers of IL 6. Constitutive production of IL 6 in early passage lines could be enhanced by the phorbol ester phorbol 12-myristate 13-acetate (PMA) and recombinant (r)IL 4 but not by rIL 1 alpha or rIL 1 beta. Nonproducing EBV-transformed lymphoblastoid cell lines could be induced to IL 6 production by PMA, rIL 1 alpha, IL 1 beta and IL 4. Among the nonproducing lines SKW6.4 was induced to IL 6 production by PMA, rIL 1 alpha, rIL 1 beta and rIL 4, whereas RPMI 8866 was induced only by PMA, to a limited extent by rIL 1 alpha and rIL 1 beta but not at all by rIL 4. There was no induction of IL 6 by any recombinant cytokine in the two Burkitt lymphoma lines but measurable production of IL 6 was induced by PMA in one of them (EB4). Cytokines which were neither enhancers nor inducers of cell lines on their own included rIL 2, rIL 5, interferon (rIFN)-gamma, native purified IFN-alpha, tumor necrosis factor (rTNF)-alpha, rTNF-beta and purified platelet-derived transforming growth factor-beta. rIL 4 synergized with either rIL 1 alpha or rIL 1 beta in the induction of IL 6 in the nonproducing line SKW6.4. Similar effects were also seen in this line with combinations of (a) rIFN-gamma and rIL 4 and (b) IFN-alpha and both rIL 1 alpha and rIL 1 beta. rIL 4, with or without rIL 1, was more effective than rIL 6 in the induction of IgM synthesis in SKW6.4 and the effect was only partially inhibited by anti-IL 6 antiserum at a dose which totally inhibited IL 6-induced IgM production. Normal peripheral blood lymphocyte populations pre-activated by anti-immunoglobulin rosetting exhibited enhanced production of IL 6 in the presence of rIL 4 and PMA but not in the presence of rIL 1, in contrast to the behavior of adherent mononuclear blood cells which showed IL 4-induced down-regulation of IL 6 production.(ABSTRACT TRUNCATED AT 400 WORDS)

Restricted utilization of VH and DH genes in leukemic rabbit B cells

Polyclonal B cell leukemias have been generated in 17- to 20-day old Emu-myc transgenic rabbits. To analyze the repertoire of VH genes utilized in early B cells, eight VDJ genes were cloned from these leukemic cells. The nucleotide sequences of these genes indicated that seven of the eight VDJ genes encoded prototype VHa1, VHa2 or VHa3 allotypes. The two VDJ genes encoding VHa1 molecules had VH segments with identical nucleotide sequences; similarly, the VH segments of the four VDJ genes encoding VHa2 molecules were identical, with the exception of a single base pair. These data suggest that a limited repertoire of VH genes were utilized in the generation of these VDJ genes. The DH segments of these genes were limited to two DH families, D1 and D2, indicating that a restricted repertoire of DH genes also had been utilized. Since these leukemic cells probably developed early in ontogeny, we suggest that this restricted utilization of VH and DH genes is representative of B cells from developmentally immature rabbits.

The biologic significance of human natural autoimmune responses: relationship to the germline, early immune and malignant B cell variable gene repertoire

The potential for autoreactivity that has been well documented in normal individuals implies that natural autoimmune responses must serve some physiologic function. To investigate the genetic mechanisms involved in the emergence of such responses, we have determined the sequences of heavy (VH) and light (VL) chain variable region genes for several human monoclonal autoantibodies and compared these with corresponding sequences reported for other antibodies and autoantibodies. Our data reveal that natural autoantibodies can be encoded by nonmutated germline VH and VL genes which are essentially identical to V genes expressed in early B cell ontogeny as well as in some B-lineage tumors. Taken together with other structural data on human autoantibodies, these findings suggest that natural autoimmune responses originate early in ontogeny and that such antibodies may play a regulatory role in development of the normal immune repertoire and possibly in suppressing pathogenic autoimmune or malignant responses.