Immunoglobulin VH determinants defined by monoclonal antibodies

Exon skipping without splice site mutation accounting for abnormal immunoglobulin chains in nonsecretory human myeloma

The proliferating plasma cells of patient COM with nonsecretory myeloma synthesized truncated 42 kDa gamma 1 chains made of a complete constant region but devoid of variable domain. In the absence of light chain expression, the shortened gamma chains were retained intracellularly and were subsequently degraded within 12 h. COM neoplastic plasma cells contained short gamma 1 heavy chain transcripts in which the leader peptide exon was directly joined to the CH1 exon using the regular splice sites. However, study of the productive gamma gene showed that the skipped variable exon was bounded by normal splicing signals and that the adjacent intron organization was not altered. Since this unusual splicing pattern was maintained when COM gamma gene was transfected in murine plasmocytoma cells, exon skipping possibly relates to the modified structure of COM variable region. The latter showed a 2-base pair deletion introducing a translation frameshift in the VH region and a DNA insertion at the VH-DJH junction consisting in a perfect duplication of the first 54 nucleotides of the recombined DJH segment. The lack of light chain production by COM cells was explained by alterations of the variable region of the rearranged kappa gene leading to abnormally spliced transcripts.

Monoclonal anti-VH141 antibodies that specifically recognize the heavy chain variable region of, and are closely related to, MOPC141 myeloma protein whose VH gene belongs to VHQ52 family

To raise monoclonal antibodies that specifically recognize the heavy chain variable region of MOPC141 myeloma protein (VH141), which belongs to VHQ52 family, rats were immunized with Fd'-conjugated keyhole limpet haemocyanin (KLH) (Fd': Fd' fragments of MOPC141), and the spleen cells were fused with mouse myeloma cells. The resulting 900 hybridomas were screened for antibody activity against Fd'1 fragments having no constant H-chain sequences, which were prepared by cleavage of the Fd' fragments with cyanogen bromide, and two monoclonal antibodies, designated 3-2-7h and 3-5-6f, were obtained. Radioimmunoassay inhibition test showed that the two monoclonal antibodies specifically recognized the VH141, but each was directed to a different determinant on the VH141. When the functional VH gene of Abelson virus-transformed mu-producing pre-B cells, which could be strongly stained with 3-5-6f monoclonal antibody, was cloned and sequenced, the VH gene was closely relate to that of MOPC141 (88% and 94% homology at amino acid and DNA level, respectively). Taken together, the results indicated that 3-2-7h had high specificity only for the VH141, whereas 3-5-6f specifically reacted not only with the VH141 but also with the VH region closely related to that of MOPC141, and that both the monoclonal anti-VH141 antibodies were specific for a limited range of VH regions within the VHQ52 family rather than being VHQ52 family specific. These monoclonal anti-VH141 antibodies should be very useful to determine at a single cell level by immunofluorescence the usage of the VH gene(s) identical or closely related to that of MOPC141 during early B-cell development.

A mouse monoclonal antibody reactive preferentially with human IgM lambda

In analyzing mouse monoclonal antibodies (mAb) against a human IgM kappa paraprotein, we found an unusual mAb (LP4; gamma 2b kappa isotype) that reacted in an enzyme linked immunosorbent assay with all 5 IgM lambda but not with 8 IgM kappa or other myelomas. Neither isolated mu heavy nor lambda light chains were reactive with LP4 mAb. By immunofluorescence, LP4 mAb identified approximately 30% of IgM+ B cells and approximately 40% of mitogen-stimulated, IgM+ plasma cells from 4-7 normal blood samples. All LP4+ cells were IgM+. Biosynthetic analysis of the plasma cells revealed that LP4 mAb recognized most IgM lambda and a very minor proportion of IgM kappa molecules. This mAb provides a useful marker for the analysis of pre-B and B cell differentiation.

Rabbit antisera to the variable region domains of an anti-alpha(1----6) dextran using E. coli-produced VL and VH fusion proteins as immunogens

Bacteria were engineered for the expression of mouse immunoglobulin light chain variable region (VL) and heavy chain variable region (VH) fusion proteins. cDNAs encoding the VL and VH of anti-alpha(1----6)dextran hybridoma protein 19.22.1 were inserted into the pATH 10 prokaryotic expression vector downstream of trp operon sequences. V domains joined to approximately 330 amino acids of the trp E gene product encoded by the expression plasmids accumulated at high levels in E. coli. In addition, the VL domain was expressed with a 15 amino acid extension at low levels in lon mutant bacteria. The trp E-VL and trp E-VH proteins were used to raise antisera in rabbits and the V specificity of the sera demonstrated.

Comparison of enteric adenovirus infection in various human cell lines

Growth of the fastidious enteric adenoviruses 40 and 41 was compared in different human cell lines. Purified virions were used to infect the following cell lines: A549; KB; Chang's conjunctiva; 293; HeLa. Both types of enteric adenovirus were infectious for each cell line, with the exception of adenovirus 40 in HeLa cells. Relatively low infectious titers were obtained from each cell type following infection with adenovirus 40 (TCID50 average = 10(-1.5)), whereas adenovirus 41 replicated to significantly higher titer (TCID50 average = 10(-3.0)). For both viruses, the highest infectious titers were obtained with A549 and KB cells. A time course experiment performed to quantitate the amount of hexon present in A549 and KB cells infected with each virus indicated that while the kinetics of accumulation were similar for both viruses, the concentration of type 41 hexon was significantly greater than that for type 40 in either cell line. The concentration of type 41 hexon was similar in each cell type; for type 40, a greater concentration of hexon was obtained in the A549 cell line than in the KB cells. The results indicate the distinct replication characteristics exhibited by adenovirus 40 are not due to a restriction in a specific host cell, and, because purified virions were used, not attributable to interference that might occur with co-infection from multiple viruses present in the same clinical specimen. We conclude the differences observed in the replication of these viruses are independent of host cell type and are associated, uniquely, with each virus.

Branhamella catarrhalis activates human B lymphocytes following interactions with surface IgD and class I major histocompatibility complex antigens

Branhamella catarrhalis initiated DNA synthesis in human blood or spleen cells enriched for B lymphocytes but did not activate T-lymphocyte-enriched fractions. Monoclonal antibodies were used to determine which B-cell surface molecules were of importance for the activation signal. The addition of monoclonal antibodies reactive with IgD, HLA class I antigens, and B2-microglobulin to B lymphocyte cultures selectively inhibited the B-lymphocyte response to B. catarrhalis. Antibody binding to IgD and class I antigens did not inhibit B-cell proliferation following stimulation with anti-IgM beads, Staphylococcus aureus, or Epstein-Barr virus. This suggests that surface IgD is of major importance for B-lymphocyte stimulation by B. catarrhalis. Since B. catarrhalis binds HLA-ABC containing liposomes it is suggested that a similar binding of B. catarrhalis to HLA-ABC on the surface of B lymphocytes serves as an accessory factor that stabilizes the binding of B. catarrhalis to surface IgD. Activation of human B lymphocytes by B. catarrhalis resulted in changes of cell surface molecules that were quantitatively and qualitatively similar to those that resulted from the activation by S. aureus. Therefore although these two bacteria appear to activate B cells in a similar manner, they induce B-cell proliferation through interactions with different cell surface structures.

Precursor B cells transformed by Epstein-Barr virus undergo sterile plasma-cell differentiation: J-chain expression without immunoglobulin

Human bone marrow cells were depleted of B lymphocytes to enrich for precursor B cells that could be transformed with Epstein-Barr virus. Transformed immunoglobulin-negative precursors either maintained their immunoglobulin genes in the germ-line configuration or had undergone DJ or abortive VDJ rearrangements (V, D, and J represent variable, diversity, and joining gene segments). All cell lines and their derivative clones, even those with no detectable immunoglobulin gene rearrangements, generated subpopulations of cells that produced high levels of joining (J) chain when analyzed by immunoprecipitation after biosynthetic labeling and by blot hybridization of cytoplasmic RNA. Morphologic and immunofluorescence analyses revealed that J-chain production was confined to clonal progeny that had exited the cell cycle to undergo plasma-cell differentiation. Analysis of cell surface antigens revealed expression of several B-cell maturational markers, including complement receptor type 2 (CR2) and plasma cell antigen 1 (PCA-1). Epstein-Barr virus can thus transform B-cell progenitors, allowing them to proliferate and undergo terminal B-cell differentiation coupled with J-chain expression. These events appear to occur independently of the immunoglobulin gene status of the transformed cells.

Circulating immune complexes and immunoglobulin A rheumatoid factor in patients with mesangial immunoglobulin A nephropathies

Circulating immune complexes (CIC) containing IgA and C3 were elevated in 48% of IgA nephropathy patients; IgA1 was the predominant subclass. IgA1-IgG CIC were detected in 44%, IgA2-IgG CIC in 7%, and IgM-IgA1 CIC in 16% of the patients. No IgM-IgA2 CIC were detectable. Sucrose gradient ultracentrifugation indicated that IgG-IgA1 CIC were predominantly of intermediate (13-19S) size whereas IgA1-C3 CIC sedimented from 11S to 19S. At acid pH, isolated CIC revealed the presence of substantial amounts of 7S IgA. One third of the patients had elevated serum IgA rheumatoid factor (RF) of both polymeric and monomeric forms despite normal levels of IgM-RF; 87% of patients with elevated IgA-RF had IgA1-IgG CIC. These results indicate that the IgA1 component of CIC in patients with IgA nephropathy is not necessarily of mucosal origin and suggest that a portion of these CIC consists of IgA RF immunologically complexed with autologous IgG.

Clathrin structure characterized with monoclonal antibodies. I. Analysis of multiple antigenic sites

Three monoclonal antibodies that react with previously undefined antigenic determinants on the clathrin molecule have been produced and characterized. They were isolated from a fusion between myeloma cells and popliteal lymphocytes from SJL mice that had received footpad injections of human brain clathrin. This protocol was chosen to favor the production of antibodies to poorly immunogenic proteins and thereby increase the repertoire of anti-clathrin monoclonal antibodies. One antibody (X16) reacts preferentially with the heavier of the two clathrin light chains (LCa) when it is not associated with heavy chain. This specificity is different from that of the anti-LCa antibody, CVC.6, which has preferential reactivity with heavy chain-associated LCa. In addition, X16 and CVC.6 bound simultaneously to LCa, confirming that they react with different sites. The other two antibodies produced, X19 and X22, react with two different determinants on the clathrin heavy chain, based on immunoprecipitation, Western blot, and binding studies. Competitive binding studies with anti-clathrin monoclonal antibodies showed that they define a total of five distinct antigenic determinants on bovine clathrin.

Immunoglobulin gene rearrangements and deletions in human Epstein-Barr virus-transformed cell lines producing different IgG and IgA subclasses

During differentiation B lymphocytes may switch from the expression of surface IgM to the synthesis of IgG, IgA, or IgE isotypes by using a different heavy chain constant region (CH) gene. The molecular mechanisms by which switching occurs remain controversial. Rearrangements and deletions of CH genes 5' to the expressed gene have often been observed in the mouse and, more recently, in human cells that have switched isotypes. We have used human JH, C micro, C gamma, and C alpha probes to examine the extent of the deletions and rearrangements in clones of Epstein-Barr virus-transformed human cells that produce IgG1, IgG3, IgG4, or IgA1. Though deletions of CH genes 5' to the expressed CH gene were consistently observed, the rearrangement process appeared to be highly variable for the nonproductive CH gene locus: deletion or persistence of 5' CH genes, combinations of deletion and duplication of 5' genes, and deletions extending to 3' CH genes. Our results reveal an unexpected lack of specificity in the DNA deletions in cells that have undergone isotype switching.

Immunogenicity and antigenicity of immunoglobulins. XII. Intact light chain and heavy chain isotype-restricted Vk-associated epitopes

Immunization with intact IgG has allowed the isolation of four hybridomas producing antibodies recognizing epitopes expressed within subpopulations of human kappa light chains unrelated to known polymorphisms (Km) and previously defined V-region subgroups. The V-region-associated epitopes recognized are conformation-dependent, being expressed on intact light chain but not on isolated VK or CK fragments. The frequency of expression within paraprotein panels of different heavy chain isotypes varied between individual antibodies. An epitope recognized by B2A6, expressed by greater than 85% IgGK paraproteins, was not represented in 16 IgM paraproteins tested, suggesting that association of VK with mu chains does not result in display of the epitope recognized, or alternatively, that selective association between VK and CH gene products occurs. These data contrast with the reactivity of other McAb for CK epitopes which were reactive with isolated CK fragments, and for all kappa-bearing paraproteins, regardless of heavy chain isotypes.

The VKIIIb light chain sub-subgroup: restricted association with mu heavy chain in normal human serum

The VKIII human kappa light chain subgroup has been serologically and structurally divided into two sub-subgroups, VKIIIa and VKIIIb. VKIIIb has been shown by others to be strikingly prevalent in IgM autoantibodies, but no studies have been performed to determine heavy chain isotype association with VKIIIb light chain in normal human serum. The VKIIIb sub-subgroup was shown here to be associated with mu heavy chain in normal human serum, but was not detected in association with gamma or alpha heavy chain. Approximately 25 +/- 15% of IgM-kappa was determined to be VKIIIb. Both intact IgG and purified light chains from pooled IgG did not bind monoclonal anti-VKIIIb, indicating that the determinants recognized by anti-VKIIIb are not merely masked in intact IgG. These results are the first report of a light chain sub-subgroup showing preferential association with a heavy chain isotype.

Antibody responses to lambda 1J558 and lambda 2315 light chains. Specificity and genetic regulation

Specificity of BALB/c antibody responses to lambda chains of isologous myeloma proteins 315 and J558 was explored by enzyme-linked immunosorbent assay. lambda-chain binding antibodies were not detected when immunizing with assembled (H + L) myeloma proteins. However, relatively high titred IgG antibodies were elicited by free lambda 2(315) immunization. Antibodies were directed to 'hidden' determinants since binding was abrogated upon H + L assembly of chains. At least a portion of antibodies bound antigenic determinants in the variable region and cross-reacted with lambda 1 land lambda 3 chains. Free lambda 1J558 immunization induced low-titred, predominantly IgM antibodies that also only reacted with 'hidden' determinants. These determinants were most probably located in the constant (C) region and no cross-reaction to lambda 2 or lambda 3 was observed. An artefact of technical importance was noted: myeloma proteins exposed 'hidden' determinants on their lambda chains when coated directly to polystyrene walls. This artefactual exposition was lost when anti C-region antibody spacer molecules were inserted between the wall and the myeloma proteins. Antibody and T helper cell (Th) responses to free lambda 2(315) covaried significantly in various strains while antibody and Th responses to free lambda 1J558 did not. In some strains, weak antibody responses were detected without detectable Th.

Evidence for the presence of idiotype-bearing regulatory T cells in which idiotype expression does not show linkage to either IgH alleles or the MHC

An anti-idiotypic antiserum was raised in rabbits to a monoclonal antibody with specificity for one of the two antigenic determinants on the ferredoxin (Fd) molecule. The monoclonal antibody (Fd-B2) was derived from fusion of spleen cells from Fd-immune B10.BR (H-2k, Ighb). Examination of an extensive number of samples of Fd-immune serum from B10.BR and other mouse strains established that the Fd-B2 idiotype is essentially never present in such sera in detectable concentrations (greater than 30 ng/ml). Administration of the anti-idiotypic antibody (anti-Fd-B2) i.v. to B10.BR mice, or treatment of B10.BR T cell-enriched populations with anti-Fd-B2 + C prior to adoptive transfer to irradiated B10.BR recipients followed by challenge with Fd resulted in a significant increase in the production of anti-Fd antibodies. This effect was specific and was not reflected by a change in expression of the Fd-B2 idiotype in the antibody produced. Similarly, injection of 10 micrograms of Fd-B2 into B10.BR mice resulted in an enhanced anti-Fd response. When similar experiments were carried out using B10.D2 mice (H-2d, Ighb), which are genetic non-responders to Fd, it was observed that treatment which anti-Fd-B2 followed by challenge with Fd resulted in production in treated animals of significant levels of antibody to Fd. Again, the antisera thus produced did not contain detectable levels of the Fd-B2 idiotype. Further experiments using high responder (H-2k) mice with Igh allotypes differing from the B10 strains (C57/BR, Igha, and RF/J, Ighc), showed that treatment of these animals with anti-Fd-B2 also resulted in a highly significant enhancement of the anti-Fd response. These data imply that the anti-idiotypic antiserum (anti-Fd-2B) is exerting its influence by acting on an id + population of T cells and that the expression of this id is not dependent on genetic linkage to either the H-2 or the Igh loci.

Specificity of IgM antibodies to pooled human F(ab')2 fragments

An isotope specific immunoassay which minimizes interference by endogenous rheumatoid factors was used to determine the specificity of IgM anti-F(ab')2 antibodies in human serum. We underscore the heterogeneity of these antibodies. While one subset of IgM anti-F(ab')2 antibodies reacts only with intact F(ab')2, another recognizes determinants present following reduction and alkylation of F(ab')2 and separation of Fd' fragments from light chains. IgM anti-F(ab')2 antibodies in sera from rheumatoid arthritis patients do not react significantly with intact pooled IgG and, therefore, probably are not anti-idiotypic antibodies. Some sera, but not all, contain elevated levels of antibodies that are crossreactive with rabbit F(ab')2. Such crossreactive antibodies may interfere with assays which utilize F(ab')2 fragments of rabbit antibodies specific for antigens of clinical relevance.

Monoclonal antibodies reactive with idiotypic and variable-region specific determinants on human immunoglobulins

Monoclonal antibody JG-B1, specific for the human VKIIIb sub-subgroup of L chains, and JG-B4 specific for an idiotypic determinant on Glo, a monoclonal human IgM-VKIIIb anti-IgG, were produced and characterized. The VKIIIb determinant was detected on L chains alone and intact immunoglobulins with VKIIIb L chains. However, the idiotypic determinant was expressed only on IgM-Glo and required association of H and L chains. Binding of the immunogen Glo, to its antigen-IgG partially inhibited anti-idiotype and anti-VKIIIb binding. Cross-inhibition experiments demonstrated that intact pentameric IgM-Glo expressed one-half the number of idiotypic sites as VKIIIb determinants. However, Glo half-molecules expressed equal numbers of idiotypic and VKIIIb determinants. This is the first described monoclonal antibody produced by hybridoma technology which recognizes an antigenic determinant specific for a single variable region in intact immunoglobulin.

Monoclonal anti-VH antibodies recognize a common VH determinant expressed on immunoglobulin heavy chains from various species

Our previous work using rabbit antibodies to the variable region of MOPC315 myeloma heavy chain (VH) has indicated the existence of framework determinant(s) common to many murine heavy chains. Here we report the characterization of anti-VH monoclonal antibodies (mAb) prepared in an attempt to elucidate the nature of the common VH determinant. We immunized AKR/J mice with a purified VH315 fragment and generated somatic cell hybrids by the fusion of the immune AKR/J splenocytes with the NS1 myeloma cells. Thirty-seven common anti-VH and 57 subgroup VHI-specific hybridomas have been established and characterized. Whereas the anti-subgroup mAb seemed to react with a determinant unique to the MOPC315 (mouse VHI) subgroup, all the anti-VH mAb reacted with myeloma heavy chains of different VH subgroups, class and allotypes. Antibody competition studies revealed that the VH subgroup determinants are distinct from the common VH determinants and that both were also recognized by the rabbit polyclonal antibodies. The common VH determinants were found to be "hidden" determinants on intact immunoglobulin molecules being exposed only on isolated heavy chains. Furthermore, they are sequential determinants since they are preserved on fully denatured heavy chains. The common VH determinants are shared by immunoglobulins of a wide range of vertebrates from amphibia to man and thus represent antigenic structures which were highly conserved throughout evolution.

Epstein-Barr virus-induced immunoglobulin synthesis by B cells from individuals with late-onset panhypogammaglobulinemia

Epstein-Barr virus (EBV) transformation was used to examine the differentiation potential of circulating B cells from eight individuals with late-onset panhypogammaglobulinemia. Cytoplasmic and secreted immunoglobulins were evaluated by immunofluorescence and radioimmunoassay. EBV-infected cultures of B cells from patients and healthy controls generated similar numbers of IgM-secreting plasma cells, but relatively few IgG and IgA plasma cells were induced in cultures of patients' B cells. As further evidence of B-cell immaturity, approximately 90% of the IgA B cells in the eight patients coexpressed IgM. Clonal diversity of B cells from hypogammaglobulinemic patients was examined with a panel of mouse monoclonal antibodies directed against idiotypic and VH subgroup determinants. The frequencies of EBV-induced plasma cells exhibiting the different idiotypic and VH determinants were similar for patients and controls. The data suggest the continued generation of clonally diverse B cells that are capable of terminal plasma-cell differentiation when the normal triggering mechanisms are bypassed by EBV. The arrested differentiation at an immature B-cell stage in these hypogammaglobulinemic individuals would appear to reflect a defect in normal B-cell triggering.

Immunoglobulin heavy-chain switching in pre-B leukaemias

Immunoglobulin gene expression is initiated in pre-B cells by rearrangements of heavy-chain variable genes V, D and J, for transcription together with the constant region gene C mu (refs 1-7). The subsequent joining of light-chain V-J genes in the kappa or lambda families leads to formation of complete IgM molecules, which are then expressed on the surface of B cells. Heavy-chain isotype switching has been thought to occur later and to involve CH gene rearrangement via deletion of DNA between a switch site 5' to C mu and a switch site 5' to the downstream C gamma, C epsilon or C alpha gene expressed by a mature plasma cell. On the other hand, isotype switching has been seen in human pre-B-cell leukaemias and in a murine pre-B-cell line before light-chain gene rearrangements and without C mu gene deletion. To explore further the isotype switching in pre-B cells, we used monoclonal antibodies in immunofluorescence assays to allow unambiguous assignment of the heavy-chain isotypes expressed by individual leukaemic cells in 11 pre-B-cell leukaemias. Switching in these leukaemic clones invariably led to expression of gamma 1 heavy-chain and kappa light-chain determinants, occasionally together with gamma 4 and alpha. These results indicate a nonrandom order for heavy-chain isotype switching and for light-chain isotype expression, and also suggest that a mechanism exists for coordinating the two events.

Immunoglobulin isotype expression of normal pre-B cells as determined by immunofluorescence

We have undertaken an immunofluorescent analysis of the immunoglobulin heavy and light chains expressed by pre-B cells from normal human fetal and adult bone marrow using purified mouse monoclonal and goat antibodies to human immunoglobulin isotypes. Our results indicate that (i) the great majority of normal pre-B cells in both fetuses and adults expresses intracytoplasmic mu chains only, (ii) immunoglobulin light-chain synthesis may be initiated during a late stage in pre-B-cell development, and (iii) heavy-chain isotype switching at the pre-B-cell stage may not occur during normal B-cell development.