Heterogeneity of the BALB/c antiphosphorylcholine antibody response at the precursor cell level

B-1b Cells Have Unique Functional Traits Compared to B-1a Cells at Homeostasis and in Aged Hyperlipidemic Mice With Atherosclerosis

Immunoglobulin M (IgM) to oxidation specific epitopes (OSE) are inversely associated with atherosclerosis in mice and humans. The B-1b subtype of B-1 cells secrete IgM to OSE, and unlike B-1a cells, are capable of long-lasting IgM memory. What attributes make B-1b cells different than B-1a cells is unknown. Our objectives were to determine how B-1b cells produce more IgM compared to B-1a cells at homeostatic condition and to see the differences in the B-1a and B-1b cell distribution and IgM CDR-H3 sequences in mice with advanced atherosclerosis. Here, in-vivo studies demonstrated greater migration to spleen, splenic production of IgM and plasma IgM levels in ApoE^-/-Rag1^-/- mice intraperitoneally injected with equal numbers of B-1b compared to B-1a cells. Bulk RNA seq analysis and flow cytometry of B-1a and B-1b cells identified CCR6 as a chemokine receptor more highly expressed on B-1b cells compared to B-1a. Knockout of CCR6 resulted in reduced B-1b cell migration to the spleen. Moreover, B-1b cell numbers were significantly higher in spleen of aged atherosclerotic ApoE^-/- mice compared to young ApoE^-/- mice. Single cell sequencing results of IgHM in B-1a and B-1b cells from peritoneal cavity and spleen of atherosclerotic aged ApoE^-/- mice revealed significantly more N additions at the V-D and D-J junctions, greater diversity in V region usage and CDR-H3 sequences in B-1b compared to B-1a cells. In summary, B-1b cells demonstrated enhanced CCR6-mediated splenic migration, IgM production, and IgM repertoire diversification compared to B-1a cells. These findings suggest that potential strategies to selectively augment B-1b cell numbers and splenic trafficking could lead to increased and more diverse IgM targeting OSE to limit atherosclerosis.

The link between antibodies to OxLDL and natural protection against pneumococci depends on D(H) gene conservation

Germline D_H sequences are required for the generation of natural antibodies reactive to bacterial phosphorylcholine but not for those reactive to self-antigen.

Selection and physiological production of protective natural antibodies (NAbs) have been associated with exposure to endogenous antigens. The extent to which this association depends on germline NAb sequence is uncertain. Here we show that alterations in germline D_H sequence can sever the association between the production of self-reactive NAbs and NAbs that afford protection against a pathogen. In unmanipulated hosts, the availability of the evolutionarily conserved DFL16.1 gene segment sequence profoundly affected the serum levels of NAbs against bacterial phosphorylcholine but not oxidized low-density lipoprotein. Mice with partially altered DFL16.1 sequence could use N nucleotides to recreate the amino acid sequence associated with the classical protective T15 idiotype–positive NAbs, whereas those without DFL16.1 could not. DFL16.1 gene–deficient mice proved more susceptible to challenge with live Streptococcus pneumoniae. Our findings indicate that although production of self-reactive NAbs can be independent of germline D_H sequence, their capacity to provide protection against pathogens cannot. The potential relevance of these findings for the rational design of vaccines is discussed.

Heterologous Prime-Boost HIV-1 Vaccination Regimens in Pre-Clinical and Clinical Trials

Currently, there are more than 30 million people infected with HIV-1 and thousands more are infected each day. Vaccination is the single most effective mechanism for prevention of viral disease, and after more than 25 years of research, one vaccine has shown somewhat encouraging results in an advanced clinical efficacy trial. A modified intent-to-treat analysis of trial results showed that infection was approximately 30% lower in the vaccine group compared to the placebo group. The vaccine was administered using a heterologous prime-boost regimen in which both target antigens and delivery vehicles were changed during the course of inoculations. Here we examine the complexity of heterologous prime-boost immunizations. We show that the use of different delivery vehicles in prime and boost inoculations can help to avert the inhibitory effects caused by vector-specific immune responses. We also show that the introduction of new antigens into boost inoculations can be advantageous, demonstrating that the effect of `original antigenic sin' is not absolute. Pre-clinical and clinical studies are reviewed, including our own work with a three-vector vaccination regimen using recombinant DNA, virus (Sendai virus or vaccinia virus) and protein. Promising preliminary results suggest that the heterologous prime-boost strategy may possibly provide a foundation for the future prevention of HIV-1 infections in humans.

Lymphoid organs for peritoneal cavity immune response: milky spots

Milky spots are located in the omentum of the peritoneal cavity and their classification as lymphoid organs has been debated. In this issue of Immunity, Rangel-Moreno et al. (2009) provide compelling data to consider them as unique secondary lymphoid organs.

C-reactive protein enhances immunity to Streptococcus pneumoniae by targeting uptake to Fc gamma R on dendritic cells

C-reactive protein (CRP) is an acute phase reactant with roles in innate host defense, clearance of damaged cells, and regulation of the inflammatory response. These activities of CRP depend on ligand recognition, complement activation, and binding to FcgammaR. CRP binds to phosphocholine in the Streptococcus pneumoniae cell wall and provides innate defense against pneumococcal infection. These studies examine the effect of this early innate defense molecule on the development of Abs and protective immunity to S. pneumoniae. Dendritic cells (DC) initiate and direct the adaptive immune response by integrating innate stimuli with cytokine synthesis and Ag presentation. We hypothesized that CRP would direct uptake of S. pneumoniae to FcgammaR on DC and enhance Ag presentation. CRP opsonization of the R36a strain of S. pneumoniae increased the uptake of bacteria by DC. DC pulsed with untreated or CRP-opsonized R36a were transferred into recipient mice, and Ab responses were measured. In mice challenged with free R36a, CRP opsonization resulted in higher secondary and memory IgG responses to both phosphocholine and pneumococcal surface protein A. Furthermore, mice immunized with DC that had been pulsed with CRP-opsonized R36a showed increased resistance to intranasal infection with virulent S. pneumoniae. The effects of CRP on Ag uptake, Ab responses, and protection from infection all required FcR gamma-chain expression on DC. The results indicate that innate recognition by CRP enhances effective uptake and presentation of bacterial Ags through FcgammaR on DC and stimulates protective adaptive immunity.

Analysis of binding sites in human C-reactive protein for Fc{gamma}RI, Fc{gamma}RIIA, and C1q by site-directed mutagenesis

Human C-reactive protein (CRP) is a classical, acute phase serum protein synthesized by the liver in response to infection, inflammation, or trauma. CRP binds to microbial antigens and damaged cells, opsonizes particles for phagocytosis and regulates the inflammatory response by the induction of cytokine synthesis. These activities of CRP depend on its ability to activate complement and to bind to Fcgamma receptors (FcgammaR). The goal of this study was to elucidate amino acid residues important for the interaction of CRP with human FcgammaRI (CD64) and FcgammaRIIa (CD32). Several mutations of the CRP structure were studied based on the published crystal structure of CRP. Mutant and wild-type recombinant CRP molecules were expressed in the baculovirus system and their interactions with FcgammaR and C1q were determined. A previous study by our laboratory identified an amino acid position, Leu(176), critical for CRP binding to FcgammaRI and work by others (Agrawal, A., Shrive, A. K., Greenhough, T. J., and Volanakis, J. E. (2001) J. Immunol. 166, 3998-4004) determined several residues important for C1q binding. The amino acid residues important to CRP binding to FcgammaRIIa were previously unknown. This study newly identifies residues Thr(173) and Asn(186) as important for the binding of CRP to FcgammaRIIa and FcgammaRI. Lys(114), like Leu(176), was implicated in binding to FcgammaRI, but not FcgammaRIIa. Single mutations at amino acid positions Lys(114), Asp(169), Thr(173), Tyr(175), and Leu(176) affected C1q binding to CRP. These results further identify amino acids involved in the binding sites on CRP for FcgammaRI, FcgammaRIIa, and C1q and indicate that these sites are overlapping.

Levels of natural IgM antibodies against phosphorylcholine in healthy individuals and in patients undergoing isolated limb perfusion

Natural IgM antibodies against phosphorylcholine (anti-Pc IgM) resemble C-reactive protein (CRP) regarding specificity and have gained increasing attention because of their supposed role in clearance of damaged cells and in cardiovascular disease. In order to quantify these antibodies in human plasma, we have developed an ELISA system, in which p-aminophenylphosphorylcholine (PCH) coupled to human serum albumin (HSA) was coated on microtiters plates. Human plasma or serum samples were incubated in the plates, after which bound anti-Pc IgM was detected with mouse anti-human IgM-HRP. Pre-incubation of plasma with competitors such as phosphorylcholine, phosphorylethanolamine, phosphorylserine or glycine-HSA, confirmed that the ELISA was specific for anti PC IgM. Levels of anti Pc IgM in a cohort of healthy donors differed by more than 100-fold, whereas the fluctuation of anti-Pc IgM levels in individuals over time was small (coefficient of variation between 6% to 25%). Furthermore, there was no correlation between CRP and anti-Pc IgM in this cohort. Levels of anti-Pc IgM in the normal donors correlated significantly with IgM binding to apoptotic cells. To test the hypothesis that anti-Pc IgM can bind to neo-antigens expressed on necrotic or apoptotic cells, anti-Pc IgM was also quantified in patients with tumors undergoing isolated limb perfusion with tumor necrosis factor-alpha (TNF-alpha). Following this procedure, a significant decrease of circulating anti-Pc IgM relative to total IgM was found in all five patients tested. In conclusion, we have developed a specific and reproducible ELISA for anti Pc IgM quantification. Fluctuation of levels of these natural antibodies over time in healthy individuals was limited, although the variation among individuals was large. Significant decreases of levels of anti-Pc IgM were found to occur during tissue damage.

The M603 idiotype is lost in the response to phosphocholine in terminal deoxynucleotidyl transferase-deficient mice

The majority of anti-phosphocholine (PC) antibodies induced by the PC epitope in Proteus morganii (PM) express the M603 idiotype (id), which is characterized by an invariant Asp to Asn substitution at the V(H):D(H) junction. To elucidate the molecular basis by which M603-like B cells acquire the mutations resulting in this invariant substitution, we analyzed the immune response to PC-PM in terminal deoxynucleotidyl transferase (TdT) gene knockout (KO) mice. In the absence of TdT, T15-id antibodies comprised 80-100% of the primary response to PC-PM. Less than 10% of the response in wild-type mice is T15-id(+). In TdT KO mice, the secondary response to PC-KLH was higher than in wild-type mice and was dominated by the germ-line T15-id. About 10% of this response, in both TdT KO and wild-type mice, comprised M167-id(+) antibodies. Additionally, none of the functionally rearranged V1/DFL16.1/J(H)1 cDNA isolated from PC-PM-immunized TdT KO mice showed the Asp/Asn substitution characteristic of PC-binding, PC-PM-induced M603-like antibodies. These data indicate that production of M603-id antibody is TdT dependent, while generation of M167-id antibody is TdT independent, and that in the absence of competition from M603-like B cells, T15-id B cells can respond to PC-PM.

T15-idiotype-negative B cells dominate the phosphocholine binding cells in the preimmune repertoire of T15i knockin mice

T15i knockin (KI) mice express a H chain that is encoded by a rearranged T15 VDJ transgene which has been inserted into the J(H) region of chromosome 12. This T15H chain combines with a kappa22-33 L chain to produce a T15-Id+ Ab having specificity for phosphocholine (PC). Inasmuch as T15-Id+ Abs dominate the primary immune response to PC in normal mice, it was surprising to find that 80% of the PC-dextran-binding B cells in unimmunized homozygous T15i KI mice were T15-Id-. Analysis of L chains expressed in these T15-Id-, PC-specific B cells revealed that two L chains, kappa8-28 and kappa19-15, were expressed in this population. The V(kappa) region of these L chains was recombined to J(kappa)5, which is typical of L chains present in PC-specific Abs. When T15i KI mice were immunized with PC Ag, T15-Id+ B cells expanded 6-fold and differentiated into Ab-secreting cells. There was no indication that the T15-Id- B cells either proliferated or differentiated into Ab-secreting cells following immunization. Thus, T15-Id- B cells dominate the PC-binding population, but they fail to compete with T15-Id+ B cells during a functional immune response. Structural analysis of T15H:kappa8-28L and T15H:kappa19-15L Abs revealed L chain differences from the kappa22-33 L chain which could account for the lower affinity and/or avidity of these Abs for PC or PC carrier compared with the T15-Id+ T15H:kappa22-33L Ab.

CXCL13 is required for B1 cell homing, natural antibody production, and body cavity immunity

B1 cells are a predominant cell type in body cavities and an important source of natural antibody. Here we report that in mice lacking the chemokine, CXCL13, B1 cells are deficient in peritoneal and pleural cavities but not in spleen. CXCL13 is produced by cells in the omentum and by peritoneal macrophages, and in adoptive transfers, B1 cells home to the omentum and the peritoneal cavity in a CXCL13-dependent manner. CXCL13(-/-) mice are deficient in preexisting phosphorylcholine (PC)-specific antibodies and in their ability to mount an anti-PC response to peritoneal streptococcal antigen. These findings provide insight into the mechanism of B1 cell homing and establish a critical role for B1 cell compartmentalization in the production of natural antibodies and for body cavity immunity.

The impact of H2-DM on humoral immune responses

H2-DM (DM, previously H2-M) facilitates the exchange of peptides bound to MHC class II molecules. In this study, we have used H2-DM-deficient (DM(-/-)) mice to analyze the influence of DM in the priming of B cell responses in vivo and for Ag presentation by B cells in vitro. After immunization, IgG Abs could be raised to a T-dependent Ag, 4-hydroxy-5-nitrophenylacetyl-OVA, in DM(-/-) mice, but closer analysis revealed the IgG response to be slower, diminished in titer, and composed of low-affinity Abs. The Ab response correlated with a vast reduction in the number of germinal centers in the spleen. The presentation of multiple epitopes by H2-A(b) from distinct Ags was found to be almost exclusively DM-dependent whether B cells internalized Ags via fluid phase uptake or using membrane Ig receptors. The poor B cell response in vivo could be largely, but not completely restored by expression of a H2-Ea(d) transgene, despite the fact that Ag presentation by H2-E(d/b) molecules was found to be highly DM dependent. Hence, while substantial Ab responses can be raised in the absence of DM, this molecule is a crucial factor both for Ag processing and for the normal maturation of T-dependent humoral immune responses in vivo.

The IgG2a/IgA produced by the murine T560 B lymphoma that arose during a graft-versus-host reaction is polyreactive and somatically mutated

In mice undergoing a graft-versus-host (GVH) reaction, donor T cells responding to the host's MHC antigens induce polyclonal activation of the host's B cells and secretion of their antibodies and autoantibodies. T560, a CD5- B lymphoma that arose in the gut-associated lymphoid tissue (GALT) of a (B10 x B10.H2aH4(b)pWts) F1 hybrid mouse that had been injected with parental B10.H2aH4b splenocytes, is of particular interest because it produces switched, heavily mutated, but, nevertheless, polyreactive immunoglobulin. T560 bears and contains IgG2a but switches to IgA spontaneously. The T560 Ig variable region is encoded by a V186.2-related VH gene, juxtaposed to DFL 16 and J(H)1, and by a Vkappa gene of the Vkappa 4/5 group juxtaposed to Jkappa1. Both VH and VK are heavily mutated. The IgA binds to polystyrene, to p-azophenyl-phosphorylcholine (PC)-conjugated keyhole limpet hemocyanin (KLH) (PC-KLH), to 2,4,6 trinitrophenylated (TNP)-KLH and to human TNF-beta but not to KLH, human TNF-alpha, or any of several other Ags tested. Hapten inhibition experiments indicate that the polystyrene, PC- and TNP-binding sites do not overlap. The switched isotypes and heavy load of somatic mutations found in the T560 IgG2a/IgA suggest that T cell-dependant somatic selection of the T560 precursor B cell may have been superimposed on polyclonal B cell activation originally associated with the GVH.

Inflammatory potential of C-reactive protein complexes compared to immune complexes

C-reactive protein (CRP) is an acute phase serum protein that binds to phosphocholine (PC) and to components of damaged tissue. CRP resembles antibody in that it binds to ligands and activates the classical complement pathway. To compare the processing of CRP complexes to that of IgG complexes, we have prepared complexes containing the same ligand, PC-conjugated BSA, and IgG antibody to either BSA or CRP. We previously demonstrated similar complement-mediated binding of these complexes to erythrocyte complement receptors. CRP and IgG also bind to receptors on neutrophils (PMN), providing another possible pathway for clearance of ligands. PMN binding of IgG complexes can lead to activation with damaging inflammatory consequences. In the present report we have used CRP and IgG complexes containing PC-BSA to compare binding to PMN and activation of PMN adherence to endothelial cells. The results indicate that CRP complexes do not activate PMN whereas IgG complexes do. Binding assays indicate that there is substantially greater binding of IgG than CRP complexes to PMN.

Altered antigen presentation in mice lacking H2-O

HLA-DM catalyzes the release of MHC class II-associated invariant chain-derived peptides (CLIP) from class II molecules. Recent evidence has suggested that HLA-DO is a negative regulator of HLA-DM in B cells, but the physiological function of HLA-DO remains unclear. Analysis of antigen presentation by B cells from mice lacking H2-O (the mouse equivalent of HLA-DO), together with biochemical analysis using purified HLA-DO and HLA-DM molecules, suggests that HLA-DO/H2-O influences the peptide loading of class II molecules by limiting the pH range in which HLA-DM is active. This effect may serve to decrease the presentation of antigens internalized by fluid-phase endocytosis, thus concentrating the B cell-mediated antigen presentation to antigens internalized by membrane immunoglobulin.

The B-cell biology of aging

Although both the number and responsiveness of peripheral B cells in aged mice remain relatively intact, there are dramatic changes in B-cell generation. Alterations in B-cell development include both a skewing of V-gene utilization, especially in cells responsive to phosphorylcholine, and a decrease in the generation of various developmental B-cell subsets. The altered representation of these subsets appears to be the consequence of two developmental blocks. The first developmental block occurs during the maturation of pro-B cells and is evidenced by a decrease in the number of pre-B cells. The second developmental block occurs at the earliest stage of sIg(+)-cell maturation (sIgMvery lo). Because of this block in B-cell maturation, in spite of a decrease in incoming pre-B cells, the number of sIgMvery lo cells appears to increase in aged mice. Additionally, the time of residence of cells within this maturational stage increases dramatically, while the proportion of cells in more mature (sIgMhi) stages of bone marrow development are decreased. In addition to the decreased number of maturing bone marrow B cells, the population of splenic B cells that represent recent bone marrow émigrés (HSAvery hi) is markedly decreased. In the face of this decrease in newly emerging cells from the bone marrow, the population of mature splenic B cells is maintained by their increased longevity.

Anti-idiotype monoclonal antibodies specific for the MOPC167 anti-phosphocholine transgene-encoded antibody

Four rat x mouse hybridomas secreting monoclonal anti-idiotypic (anti-Id) antibodies (MAb) specific for the transgene-encoded antibody of the 207-4 transgenic mouse line, which carries the VH1/V kappa 24 gene segments of the IgA, phosphocholine-(PC) specific MOPC167 myeloma, were developed from a fusion of Ag8-X63.653 mouse cells with spleen cells from a rat immunized with MOPC167 and HPCM27 anti-PC antibodies. The anti-Id MAb were shown by ELISA to be specific for PC-binding proteins of VH1/V kappa 24 H and L chains of various isotypes. They did not bind VH1/V kappa 22, VH1/V kappa 8, or VH1/V kappa 1 PC-binding proteins or other IgA or IgM myeloma proteins. Analysis by flow cytometry demonstrated that these MAb bind to the transgene-encoded membrane immunoglobulin (sIgM) as expressed on > 95% of the B220 positive 207-4 spleen cells. All four MAb were able to inhibit the binding of MOPC167 to PC conjugated to bovine serum albumin. Differences in fine specificity of binding were demonstrated by differential staining of spleen cells of the 216-7 mu kappa delta Mem MOPC167 transgenic mice. In these mice endogenous H chains associate with the transgene encoded L chain to form MOPC167 crossreactive idiotopes. Two of the MAb, 28-4-3 and 28-6-20, stained significant numbers of cells, while MAb 28-5-15 did not bind to 216-7 cells. Three of the MAb, 28-5-15, 28-6-20, and 28-4-3, when conjugated to Sepharose beads, were able to induce DNA synthesis in cultures of 207-4 transgenic spleen cells. None of the MAb were able to induce an antibody response in vivo. These MAb should prove useful in staining PC-transgenic B cells for flow cytometry studies and in defining early cellular events in the activation of idiotype positive B cells by anti-Id antibodies.

Binding of phenylphosphocholine-carrier conjugates to the combining site of antibodies maintains a conformation of the hapten

The structural basis of the binding of phenylphosphocholine haptens to antibodies was studied. This was done by preparing antibodies and testing binding to conjugates of phenylphosphocholine. The choice of haptens was made in order to evaluate the contribution of the carrier to binding, and its effect on hapten conformation in the active site. Thus, phosphocholine (PC) was diazophenyl-linked to tyrosine or histidine as single amino acid carriers and to tripeptides or octapeptides containing tyrosine or histidine as central amino acids to which PC was attached. Relative affinity was assessed by inhibition enzyme-linked immunosorbent assay (ELISA) and binding constants were determined by fluorescence quenching. Fluorinated haptens were used to determine the kinetics of binding using 19F nuclear magnetic resonance. The transferred nuclear Overhauser effect was used to characterize conformation of the bound hapten. We had previously shown that nitrophenylphosphocholine unlinked to carrier is bound in the active site as a bent structure [Bruderer, U., Peyton, D. H., Barbar, E., Fellman, J. H., & Rittenberg, M. B. (1992) Biochemistry 31, 584-589]. We show here that this same bent conformation is retained in the active site regardless of the neighboring carrier or the conformation of the hapten in the unbound conjugate. The presence of the carrier residues in the bound state does, however, influence affinity.

Transient dominance of the early primary immune response by a highly conserved B-cell clone that is distinguished by its lack of memory, high threshold of activation, and a high affinity

We establish here that the very early primary response to the hapten phthalate (Xmp) is distinguished by a restricted heterogeneity with over 80% of the anti-Xmp antibodies expressing a single well-defined cross-reactive idiotype (CRIXmp-1) associated with a previously described highly conserved clonotype that is expressed by most inbred strains of mice and many outbred mouse populations as well. The characteristic early dominance of this one clonotype in the primary response is transient. While the CRIXmp-1 clonotype is present later in the primary and throughout the secondary response, it represents only a very small proportion of the total anti-Xmp antibody population at these times. The early dominance of the single clonotype is rapidly replaced by a heterogeneous population of antibodies. Differential activation thresholds for the primary response clonotype (CRIXmp-1) and secondary response clonotypes, and the failure of the dominant primary response clonotype to expand in the secondary response (i.e., absence of memory) suggest the presence of two distinct B-cell lineages.

Characterization of the recognition specificity of autoreactive, polyspecific monoclonal antibodies obtained from spleen cells of parasite-infected BALB/c mice

We examined the specificity of four monoclonal antibodies (MoAbs) obtained from Schistosoma japonicum (1D, GAO3), Trypanosoma cruzi (TSLO), and Trichinella spiralis (TSY2) infected BALB/c mice. All four MoAbs reacted not only with autologous parasite antigens but also with various heterologous parasite antigens and normal tissues. The antigen recognition pattern seen on Western blots was almost identical in 1D and GAO3, and in TSLO and TSY2. Furthermore, certain bands were identical among all four MoAbs. The mechanisms responsible for these phenomena are discussed.

Production of anti-phosphorylcholine antibodies of the T15 idiotype in CBA/N xid mice: investigation of the defect using a T15 immunoglobulin transgene

A notable defect in CBA/N xid mice is their relative inability to make antibodies to phosphorylcholine (PC), particularly those of the T15 idiotype which predominate in the anti-PC responses of immunologically normal mice. To investigate the basis of this defect, we introduced functionally rearranged genes encoding a T15+ PC-binding immunoglobulin G antibody into the germline of these animals. Expression of these genes in the xid cells was observed, shown by the existence of a distinct population of T15+ cells (3 x 10(6)) in the spleen of the transgenic animals, and the presence of PC-binding T15+ IgG antibodies (1-15 micrograms/ml) in the serum. Mixed antibody molecules were also found, however, which were composed of both transgene-encoded and endogenously-derived chains. Existence of the T15+ cells in these animals seemed normal, since these were not depleted (to any great extent) and were immunocompetent as well. The latter was shown by the increased T15+ antibody production in the transgenic animals when stimulated with a PC-associated thymus-independent type 1 (TI-1) antigen and anti-idiotype antibodies, but not with the pneumococcal TI-2 antigen. This is similar to the PC-specific (T15-) responsiveness of normal CBA/N xid mice. Based on these results, we argue that a reason why T15+ antibodies are not normally made by CBA/N xid animals is because T15+ genes are not utilized or, as with any T15+ precursors present, selected for in these animals, in contrast to normal mice where the Lyb-5 or CD5 cells (which are absent in CBA/N xid animals) are known to be specially endowed to make such antibodies.

Age-dependent appearance of non-major histocompatibility complex-restricted helper T cells

T cells which recognize antigen in association with self major histocompatibility complex (MHC) molecules are positively selected within the thymus. This results in skewing of the T-cell repertoire toward the recognition of antigenic peptides presented by self MHC molecules. While the thymus gland involutes at a relatively young age, bone marrow function and the size of the peripheral T-cell pool are maintained with age. We have investigated the MHC restriction of helper T-cell function for B-cell production of specific antibody in mice of different ages. Splenic helper T cells from 2- to 3-month old mice immunized with phosphocholine-keyhole limpet hemocyanin conjugate were MHC-restricted as defined by their capacity to induce phosphocholine-specific antibody synthesis by syngeneic but not by allogeneic B cells. In contrast, splenic T cells from immunized 18- to 20-month-old mice induced specific anti-phosphocholine antibodies by both syngeneic and allogeneic B cells. No evidence of polyclonal immunoglobulin synthesis was detected. The ability of T cells from old mice immunized with phosphocholine-keyhole limpet hemocyanin to induce phosphocholine-specific antibody synthesis by B cells from allogeneic mice was inhibited by T cells from immunized young mice. These findings suggest that non-MHC-restricted T-cell helper activity in old mice results from the loss of T cells, present in young mice, which suppress non-MHC-restricted helper cells.

Junctional diversification in the generation of the precursor of a discrete immune response

Phosphocholine (PC)-specific antibodies that arise in the mouse in response to Proteus morganii (PM) and use V1-DFL16.1-JH1 are characterized by a number of recurring mutations. Most striking is an invariant A for G substitution in codon 95 of VH which results in an asparagine instead of aspartate at that position. Because of the apparent importance of this substitution in an anti-PC(PM) response, we wanted to determine the molecular basis for this base change. A cDNA library derived from pre-immune splenic B cells was examined for the frequency of VDJ containing the A substitution at 95 and the presence of additional point mutations in these sequences. Six different cDNA were isolated which contained an A substitution at the VD junction (frequency 0.00009); a seventh positive cDNA could not be examined. The V segments of four of these cDNA matched known germline genes and were, therefore, unmutated. Two others closely matched V in families whose members have not all been characterized, hence, it is not known whether the mutations observed are somatic or germline in origin. Sequences of 35 cDNA clones, containing the same V segment but differing in D, J and junctional nucleotides, revealed no mutations. These results indicate that the A substitution generated at codon 95 is most likely a product of V-DJ joining.

Maturation of the antibody response to a protein-coupled form of the organophosphorus toxin soman

We have analysed the serum antibody response of BALB/c mice to the organophosphorus toxin soman coupled to the protein carrier keyhole limpet haemocyanin (So-KLH) and compared the specificity of the serum antibodies to that of hybridomas described previously. The relative inhibitory capacities of various soman analogues for serum antibodies correlated with those for the monoclonal antibodies. Our results also demonstrate that immune memory to this organophosphorus hapten is stable for greater than 1 year. Interestingly, maturation of the serum antibody response is accompanied by fine specificity changes resulting in increased binding to soman-protein conjugates but not in significant changes in binding to free hapten analogues of soman. This finding suggests that contributions made by the protein carrier or bridge structure, including those made by amino acid side chains involved in the linkage, may play a significant role in the maturation process of antibodies recognizing protein-coupled organophosphorus haptens such as So-KLH. Structurally related but charge-dissimilar organophosphate haptens such as nitrophenylphosphocholine were poorly recognized, even when conjugated to protein with the same diazophenyl linkage used to conjugate soman. This is consistent with maintenance of high specificity in the memory immune response to soman-coupled protein.

Regulation of idiotype expression. II. The phenotypic diversity of T15 idiotype-bearing antibody to phosphorylcholine in response to T-dependent and T-independent antigens

The idiotypic (Id) diversity of the immune response to phosphorylcholine (PC) was studied by immunization of mice with thymus-dependent (PC-keyhole limpet haemocyanin; PC-KLH) and thymus-independent (S. pneumoniae R36a; Pn) forms of the antigen. Mice with the BALB/c genetic background (BALB/c, C.B20, and BALB.B) were used because their response to PC is dominated by immunoglobulins encoded in VH-1 and V kappa 22 genes, which uniformly express the T15 idiotype. The actual repertoire of the antibody was determined by idiotypic markers (Id) defined with monoclonal antibodies designated AB1-2, B36-82, MaId5-4, and B24-44. Previous studies from our laboratory have shown that these Id are present on T15 (VS107-1/V kappa 22) immunoglobulins only, but that they differentiate between somatic variants of the antibody molecules. We have measured the serum concentrations of these four Id after primary (1 degree), secondary (2 degree), and tertiary (3 degree) immunization; all of the Id activity was associated with the PC-binding antibody, as shown by specific immunoadsorbents. However, the levels of the Id-bearing (Id+) antibody did not correlate with each other. After immunization with PC-KLH, the AB1-2+ antibody declined precipitously, whereas the levels of B24-44 and B36-82 remained steady. A similar pattern of Id heterogeneity was seen at the level of direct antibody-plaque-forming cells from the spleen, suggesting that the idiotopic (clonal) diversification occurred already during the early IgM response. A significant portion of anti-PC antibody after the 3 degrees PC-KLH immunization was negative for all four Id, implying that the late response to the antigen involved distinct, T15-negative clones.

The adjuvanticity of gamma inulin

Gamma-inulin (g-IN) is a polymorph identified as the active component of inulin preparations that specifically activates the alternative pathway of complement (APC). The APC is central to many leucocyte functions, including B cell activation. We show here that g-IN, when formulated as a pure, endotoxin-free, fine suspension insoluble at 37 degrees C and given at 50-100 micrograms per mouse, is a potent adjuvant for both humoral and cell-mediated responses to a variety of antigens. g-IN increased secondary IgG responses five- to 28-fold (P less than 0.001), using as antigen phosphorylcholine coupled to keyhole limpet haemocyanin; subclasses IgG 2a, 2b, and 3 were boosted several hundred-fold, IgG 1 10-fold. IgM and IgA were increased four- to six-fold. Delayed hypersensitivity, by footpad swelling after secondary challenge with sheep red blood cells (SRBC), was increased more than two-fold (P less than 0.001) if g-IN was included with the primary SRBC, equivalent to increasing primary doses 10-fold. g-IN was equally active if given 5 days before the primary SRBC. Thus it is an immune stimulant rather than a depot or vehicle for antigen. Mice primed subcutaneously with 30-300 HA units of H2N2 influenza virus (strain A/JAP) and challenged intranasally with a lethal dose of H1N1 virus (strain A/WSN) all died, but if g-IN was given with the primary antigen 50% of the mice survived (P less than 0.001), a deduced but not proven boost to cytotoxic T cell-mediated immunity. Unpublished work has shown that g-IN has no adverse effects at adjuvant-active doses.(ABSTRACT TRUNCATED AT 250 WORDS)

IgM anti-erythrocyte autoantibodies specific for buried and neo-antigens using cellular-ELISA assays

The aim was to develop a cellular-ELISA assay to detect natural autoantibodies specific for bromelain-treated mouse red blood cells (BrMRBC). High, unexpected IgM titres against normal mouse red blood cells (NMRBC) were detected in day 7-14 sera of CBA mice treated with E. coli lipopolysaccharide (LPS). These "autoantibodies" bound to normal mouse red blood cells in the presence or absence of commonly used c-ELISA adhering agents. Such high reactivity to NMRBC was never detected using complement dependent haemolytic assays in earlier work in this system. The question whether these IgM alpha-NMRBC molecules were binding nonspecifically (via Fc) or specifically (via Fab) was answered indirectly by comparing the binding titres of LPS-stimulated serum and several purified IgM antibody preparations (alpha-PC, alpha-KLH, MOPC 104E) on the same antigen coated plates. The observed binding ratios (titre on antigen X: titre on NMRBC) varied widely between different antibody sources, indicative of specific binding. In addition no significant unequivocal binding against NMRBC could be detected in vivo (LPS-stimulated mice) nor could bound IgM antibody be detected in a suspension-c-ELISA assay (high binding titres to BrMRBC could be detected in the latter test system). In conventional c-ELISA assays, modification of normal erythrocyte by adhesion to plastic microtitre plates appears to expose or create "neoantigens" on NMRBC which are not encountered in suspension-type c-ELISA, nor in lytic or agglutination assays where the erythrocyte targets are in suspension at physiological pH and isotonicity.

Immune response to Trichinella epitopes: the antiphosphorylcholine plaque-forming cell response during the biological cycle

Phosphorylcholine (PC), an immunodominant component of the cell wall of certain bacteria, fungi and nematodes, is known to induce low anti-PC antibody levels during natural infection by Trichinella spiralis. This article reports a study in which spleen cells from BCF1 mice infected with Trichinella sp. larvae were found to produce large numbers of direct haemolytic plaques in response to PC conjugated to sheep red blood cells (SRBC) after muscle-encysted larvae had been killed by treatment with mebendazole. Inhibition of the response by PC-chloride, immunodiffusion and immunoelectrophoretic studies with the anti-PC IgA (TEPC-15) and anti-idiotype T15 serum assays showed the plaque-forming cell (PFC) response to be specific for PC. The absence of haemolytic plaques when unconjugated SRBC or TNP-SRBC were used as indicator cells ruled out involvement of a polyclonal response. Greatest anti-PC PFC response was found to be associated with a microsomal fraction designated FCp1, a particulate fraction behaving as a thymus-dependent antigen. The FCp1 fractions from all four strains of Trichinella employed induced anti-PC PFC responses when injected into mice. These results suggest that FCp1 is a suitable antigen for use in detailed studies of immune responses to Trichinella and related parasites.

The IgE antibody response to the phosphorylcholine hapten

The immune response to the phosphorylcholine (PC) hapten elicited by PC-keyhole limpet hemocyanin (KLH) is composed of 2 groups of antibodies with specificity to either PC or phenylphosphorylcholine which were designated as group I and II anti-PC antibodies, respectively. We demonstrate that anti-PC IgE antibody expression is restricted to group II antibodies and does not display the T15 idiotype. Accordingly anti-PC IgE antibodies recognize the same epitope (PC-phenyl) as IgG1, IgG2a and IgG2b antibodies which is different from that (PC) recognized by IgM and IgG3 antibodies. A monoclonal anti-PC IgE antibody, representing group II characteristics was established. From amino acid sequences of light chains of purified group I and II antibodies from serum as well as of monoclonal representatives thereof it appears that both populations are relatively homogenous and represent independent clonal expressions. Nevertheless the formation of anti-PC IgE antibodies in mice can be suppressed by isologous anti-T15 anti-idiotypic antiserum. This antiserum, however, crossreacts with different anti-PC antibodies including monoclonal group II anti-PC IgE antibodies and is composed of a large number of anti-idiotopes. An analyses performed with monoclonal anti-T15 idiotopes demonstrates that some but not all antibodies suppress the formation of anti-PC IgE. We conclude that syngeneically induced anti-idiotypic interactions may display regulation of a wide range of specificities affecting responses to various antigenic determinants.

Carrier-specific T cells sufficient for the expression of multiple isotypes in B cell cultures

A modified splenic fragment assay was used to assess the role of antigen-specific helper T cells in B cell isotype expression. Limiting numbers of carrier-specific helper T cells from lines or clones were injected along with a source of B cells into lethally irradiated unprimed recipients. The incidence of lodging of the T cell lines in recipient spleens at 18 h was determined by autoradiography to be 1.5 to 4.3% of the injected cells. These T cells were necessary and sufficient for the generation of T-dependent B cell responses within splenic fragments cultured in vitro with specific antigen. A comparison of isotypic responses from splenic and Peyer's patch B cells generated with the same T cell population revealed that a high proportion of the response from Peyer's patch B cells consisted of IgA antibody exclusively (46-57%) while the percentage of such responses from splenic B cells was much lower (7-10%). Thus, the isotype pattern of the response reflected the B cell source. Experiments in which cloned hemocyanin-specific T cells provided help to T-depleted spleen cells within splenic fragments from athymic recipients indicated that a single specificity of helper T cell is both necessary and sufficient to support the generation of antibody responses consisting of multiple isotypes. Isotype-specific T cells do not appear to be required in this system.

Fine specificity and idiotype expression of anti-phosphorylcholine IgE and IgG antibodies

The immune response to the phosphorylcholine (PC) hapten elicited in BALB/c mice by PC-keyhole limpet hemocyanin (KLH) is composed of 2 groups of antibodies with specificity to PC and phenyl-PC, respectively. They were designated as group I and group II anti-PC antibodies. In this report we demonstrate that anti-PC IgE antibodies elicited by PC-KLH or PC-ovalbumin belong to the group II and do not express the T15 idiotype. Anti-PC IgG1, IgG2a and IgG2b antibodies express group I characteristics in the primary response and bear the T15 idiotype. Later, after 5 weeks and 3 injections of PC-KLH or PC-ovalbumin, a change in these isotypes to group II antibodies is observed. In contrast, anti-PC IgE is a group II antibody throughout progression of the immune response. The regulation of group I and group II antibody expression in serum is independent of the genetic background of the animals.

Strain-specific silencing of a predominant antidextran clonotype family

The immune response to dextran is characterized by marked phenotypic differences among murine strains. In particular, Igha strains, as opposed to strains of other Igh haplotypes, respond relatively vigorously to dextran B1355 fraction S (DEX), producing predominantly antibodies bearing the lambda light chain, and specific for the alpha(1----3) glucose linkage. We have investigated this disparity in BALB/c (Igha) vs. C.B20 (Ighb) mice at the individual precursor cell level. Consistent with previous findings (7-9, 35, 40, 42, 43), there was a 10-fold higher frequency of lambda-bearing splenic B cells specific for the alpha(1----3) linkage in Igha mice. As with previously studied (25-27) predominant specificities, the origin of this high frequency of lambda-bearing alpha(1----3) DEX-specific B cells appears to be a reflection of a high expression of this specificity in surface Ig (sIg)-negative cells emerging from the bone marrow generative cell pool. Surprisingly, although C.B20 mice (Ighb) have a low frequency of lambda-bearing alpha(1----3) DEX-specific B cells in their mature primary splenic population, the frequency of precursor cells of this clonotype in their sIg- bone marrow cell population is equivalent to that of BALB/c sIg- cells. These cells could only be stimulated in allotype allogeneic (Igha), as opposed to allotype syngeneic (Ighb), carrier-primed irradiated recipients. This finding was confirmed by the finding that a high proportion of antidextran hybridoma cell lines derived from C.B20 bone marrow cells produced lambda-bearing alpha(1----3) DEX-specific antibodies that were IdX+. These findings have led us to conclude that the well-established phenotypic difference between Igha and Ighb mice with respect to the expression of lambda-bearing alpha(1----3) DEX-specific antibody responses is not, as previously assumed, the result of an inability of Ighb mice to generate B cells of this clonotype, but rather, is the product of environmental, possibly antiidiotypic, silencing of cells of this clonotype as they mature in Ighb mice.

In vivo polyclonal stimulation of antibody secretion by two types of bacteria

We previously proposed that one benefit of early polyclonal antibody secretion after bacterial infection might be the formation of antibodies protective against infection by a second pathogen. In order to analyse this possibility, the polyclonal and anti-phosphorylcholine (PC) plaque-forming cell (PFC) response induced by Staphylococcus aureus Cowan I (SA) was compared with the same responses stimulated by unencapsulated Streptococcus pneumonia strain R36a. S. aureus stimulated significant anti-PC PFCs, despite an inability to detect immunoassay-reactive PC on the surface of SA (present on R36a). The induction of these antibodies appeared very similar to the mechanism for producing polyclonal responses. R36a also stimulated both anti-PC and polyclonal PFCs, but by different means. In summary, our data suggest that each type of bacteria induces polyclonal and anti-PC responses through different mechanisms, and that the polyclonal antibody response stimulated by one group of bacteria can contain antibodies directed towards a second and different genus of bacteria.

Distinct functional phenotypes of cloned Ia-restricted helper T cells

Analysis of activation of phosphorylcholine (PC)-specific B cells by a large number of different cloned, self Ia-specific helper T cell (Th) clones has permitted the classification of such T cells into four distinct functional types. Types 1 and 2 induce B cells to secrete anti-PC antibody in an antigen-specific, Ia-restricted fashion. Type 3 cells induce antigen-specific, Ia-restricted B cell proliferation, but do not lead to specific antibody formation, and have been shown previously to have suppressor functions. Type 4 cells are autoreactive, and induce antigen-independent B cell activation and antibody secretion. The distinction between type 1 and type 2 Th clones was analyzed in detail. In bulk cultures, type 1 cloned lines generate an idiotypically heterogeneous anti-PC antibody response, whereas type 2 cloned lines induce a larger response that is dominated by the T15 idiotype. In limiting-dilution analyses, type 2 cells induce fourfold more T15+, PC-specific precursor B cells than do type 1 cells, and in addition, induce larger burst sizes for T15+, PC-specific B cells. Type 4 clones can also be subdivided into cells that are type 1-like, and cells that are type 2-like. These differences in functional phenotype are seen over a broad range of antigen and cell doses. Detailed analysis of the behavior of these distinct functional types of Th should allow a better understanding of the functional properties of mixed populations of antigen-primed, Ia-restricted Th cells.

Variable regions of antibodies to synthetic polypeptides--I. Characterization of an idiotope expressed on antibodies and T-cell factors

Spleen cells from a Lewis rat immunized with affinity-purified B10 anti-(T,G)-A-L antibody were fused with the non-secreting murine hybridoma SP2/0. Cell lines secreting monoclonal antibodies specific for mu- and kappa-chains, as well as an idiotope on anti-(T,G)-A-L antibodies, were isolated and characterized. The anti-mu and -kappa antibodies, are true anti-isotypes, reacting with sera from all strains of mice tested. The anti-idiotope antibodies recognize a determinant on antibodies binding a GT-containing epitope. The proportion of anti-GAT antibody bearing the idiotope varies markedly in different murine strains. A 1000-fold higher level of antibody from Igha mice than from Ighb and Ighe mice is required to give an equivalent inhibition of the idiotope-anti-idiotope reaction. Analysis of monoclonal antibodies expressing the idiotope indicates that the affinity of binding between idiotope and anti-idiotope can vary by as much as two orders of magnitude. Immunoadsorbants prepared with anti-idiotope antibody bind suppressor factor secreted by a GAT-specific T-cell hybridoma.

Studies on antibody repertoire: ontogenic development of mitogen-reactive B cells producing phosphorylcholine-specific and/or T15-associated 10/13 idiotope-positive antibodies

Very high frequencies of phosphorylcholine-specific and 10/13 idiotope-positive precursor cells were observed in spleen and liver cells polyclonally stimulated by lipopolysaccharide in BALB/c mice. These frequencies do not show any significant difference at birth, in young and adult mice, suggesting that antibody molecules analyzed arose from a single germ line heavy chain variable region gene segment. The order of magnitude of these frequencies was comparable in germ-free mice and conventionally reared BALB/c mice. Therefore, external antigenic stimulation does not seem to be involved in the establishment of antibody specificity available repertoire.

Frequencies of phosphorylcholine-specific and T15-associated 10/13 idiotope-positive B cells within lipopolysaccharide-reactive B cells of adult BALB/c mice

The frequencies of lipopolysaccharide-reactive B lymphocytes in adult BALB/c spleen cells were determined by limiting dilution experiments to be between 1 in 50 and 1 in 100. Within this reactive population, the frequencies of B lymphocytes specific for phosphorylcholine (PC) and/or binding a TEPC 15-associated idiotope-specific monoclonal antibody (10/13) were found to be between 1 in 50 and 1 in 500. Binding of these antibodies to immobilized PC or to monoclonal idiotope-specific antibodies could be inhibited by soluble PC in a solid-phase radioimmunoassay. Around half the PC-specific B cell clones were found to also bind 10/13 idiotope-specific monoclonal antibody, while the rest were either PC specific, but idiotope-negative or idiotope-positive, and unable to bind immobilized PC.

Pneumococcal cell wall phosphorylcholine elicits polyclonal antibody secretion in mice

Immunization of mice with phosphorylcholine (PC)-bearing Staphylococcus pneumoniae Type 2, strain 36a (R36a) results in both a PC-specific and a polyclonal increase in splenic plaque-forming cells. The polyclonal increase was observed in all strains tested, including those bearing an X-linked immune defect resulting in an undetectable anti-PC immune response. The magnitude of the polyclonal response is directly related to the amount of bacterial surface PC as detected by enzyme-linked immunosorbent assay. Congenitally athymic (nude) mice mount an anti-PC plaque-forming cell response after R36a immunization but fail to produce a significant polyclonal response. From our results it appears that PC on the cell wall of a bacterium acts both as a polyclonal activator and a specific antigen, stimulating each by different mechanisms.

1984: all idiotypes are equal, but some are more equal than others

Our analysis of idiotypic dominance suggests that 3 elements play an important role. The first is the genetic material that encodes the dominant idiotype. As dominant idiotypes appear to reflect germ-line-encoded sequences, one can not express a particular idiotype unless that sequence is present in the germ line. The germ-line-encoded sequences, in turn, would, I predict, be specific for commonly encountered or former environmental pathogens. The second element is the environmental antigens themselves. These antigens will induce the production of idiotype, and will prime idiotype-bearing B cells, such that idiotypic dominance emerges. In the absence of such influences, the pattern of idiotypic expression appears to differ. The third influence is regulatory. My own studies have shown that idiotype found in normal serum plays an important role in the maturation and/or function of one such cell, an idiotype-specific helper T cell. It is my working hypothesis that such cells play several roles in idiotypic dominance, but that this is the least of their important roles. Rather, such cells, being specific for idiotopes associated with antibodies specific for environmentally encountered pathogens, would be important in the priming and rapid reactivation of B cells bearing such idiotopes. As such, they speak to the basic role of the immune system, the protection of the organism from infection.

Idiotype-specific T-helper cells

In the present study we investigated the induction and fine specificity of T-helper cells that recognize idiotypes. The data presented show that both low-dose priming with anti-T15 antiserum and priming with PC-Hy are effective in stimulating T15-specific T help. Phosphorylcholine-hemocyanin priming can generate these T cells in either PC-responding or nonresponding strains of mice. Furthermore, the PC-primed T-helper cells can also recognize another anti-PC myeloma, M167, that is idiotypically different from T15. The fine specificity of the anti-PC-idiotype recognizing T-helper cells was examined by studying the effect of in vitro inhibitors on the T-cell help. Both PC and PC-BSA as well as T15 and M167 had an inhibitory effect on the T help. Free T15 and M167 heavy chains also blocked the helper activity for T15; T15 and M167 light chains had no effect, however. Viewed collectively, these results show that PC-Hy priming induces T-helper cells that recognize idiotypic determinants common to both T15 and M167, and that the proteins' H chain is the major structural component of the determinant. Finally, the generation of these idiotype-recognizing T cells was found to occur by way of a T-T interaction loop, based on the finding that T-helper cells are induced by PC-Hy priming in animals that lack PC-responding B cells.

Role of variable region gene expression and environmental selection in determining the antiphosphorylcholine B cell repertoire

To evaluate the role of environmental selective processes, as opposed to variable region gene expression, in the determination of B cell repertoire expression, we have assessed the phosphorylcholine (PC)-specific repertoire of precursor cells that remain in bone marrow cell populations after the removal of surface immunoglobulin (sIg)-bearing cells. Such cells are assumed to represent a stage in B cell maturation before the expression of sIg, and thus at a time when they have not as yet interfaced with environmental influences that operate through sIg receptors such as antigenic stimulation, tolerance, or antiidiotypic regulation. The repertoire as expressed in these cells, therefore, should reflect the readout of immunoglobulin variable region genes as they are expressed in progenitors to B cells. The results of these studies indicate that, as in mature primary B cell pools of BALB/c mice, the majority of PC-responsive sIg- bone marrow cells are of the T15 clonotype. Thus, environmental selective mechanisms would not appear to be required for the high frequency of B cells of the T15 idiotype in the primary B cell repertoire of BALB/c mice. Analysis of the sIg- bone marrow cells in (CBA/N X BALB/c)F1 male mice demonstrated that the deficit of PC-responsive mature B cells, which is a characteristic of this murine strain, must occur after receptor expression, since a normal frequency of PC-responsive and T15-expressing cells is present in their sIg- bone marrow population. Finally, these same mice were used to obtain bone marrow cell preparations from individual leg bones, so as to permit an analysis of the occurrence of T15+ and T15- clonotypes within individual bone marrow populations. The findings from these studies indicate that T15+ B cells occur as a high frequency event within bone marrow generative cell pools. Furthermore, bone marrow populations that are positive for PC-responsive precursor cells often display multiple copies of such precursor cells that are exclusively either T15+ or T15-. This finding indicates that clonal expansion of cells within the B cell lineage apparently occurs before immunoglobulin receptor acquisition.

Interrelationship of primed B cells with the potential for IgE and/or IgA expression

The relationship between the pathways of B cell differentiation leading to IgE or IgA expression was analyzed by assessing the isotype potential of primed B cells as revealed over many generations of clonal outgrowth in splenic fragment cultures. Cells from (CBA/N X BALB/C) F1 male and female mice primed with phosphocholine (PC)-hemocyanin (Hy) and given a secondary stimulus with PC-Hy or PC-determinants via an Ascaris infection gave rise to a large proportion (25-48%) of clones which expressed anti-PC IgE along with any one or mixture of other isotypes, especially IgG and/or IgA. Accompanying the appearance of these cells in the Peyer's patches following Ascaris infection was the steady rise in IgA committed cells over a 12 week period. The potential to express IgE seems to be a normal feature of the development of secondary or memory cells. The coexpression of IgE randomly with all other isotypes supports a linear rather than a branched pathway of B cell differentiation. Ascaris or PC-determinants given to F1 mice were not unique in their ability to prime cells with the potential for IgE expression. Stimulation of BALB/c mice with two low doses of N-acetyl-glucosamine-conjugated hemocyanin (GlcNAc-Hy) primed cells in vivo generated a high proportion (63%) of clones in vitro that expressed IgE and most of these exclusively coexpressed IgA (16/26) suggesting a progressive restriction in isotype potential. Cells which gave rise to IgE producing clones specific for the priming hapten did not support the expression of IgE by clones of other specificities costimulated in vitro (anti-inulin, anti-beta-galactosyl). Thus the potential to express IgE seems to be both an inherent property of the B cells and under hapten-specific or hapten-linked regulation.

Subpopulations of B cells distinguished by cell surface expression of Ia antigens. Correlation of Ia and idiotype during activation by cloned Ia-restricted T cells

We have investigated in vitro the induction of antibody responses to phosphorylcholine (PC) by cloned T helper (Th) cell lines. The cloned Th cells are antigen specific, in this case ovalbumin (OVA), self-Ia recognizing, and induce antibody secretion only if the hapten, PC, is physically linked to the carrier (OVA) molecule. The plaque-forming cell (PFC) response generated in the presence of cloned Th cells is idiotypically diverse with 5-40% of the secreting B cells bearing the TEPC-15 (T15) idiotype. The interaction of the cloned Th cells and unprimed B cells requires recognition of B cell surface Ia glycoproteins for all B cells activated to secrete anti-PC antibody, whether they be T15-bearing or not. More importantly, however, effective interaction between a cloned Th cell and a B cell is determined by the quantity of B cell surface Ia glycoproteins. Our results indicate that quantitative differences in B cell surface Ia antigens are directly related to B cell activation by the cloned Th cell. The high Ia density B cells are most easily activated by cloned Th cells, and these appear to be mainly non-T15-bearing. These data suggest that the failure of cloned Th cells to effectively activate T15-bearing B cells in vitro may be due to the lower relative Ia density of these B cells and therefore to their inability to interact effectively with cloned Ia-recognizing Th cells. These results imply that monoclonal T cells may distinguish between T15-bearing and non-T15-bearing B cells based on their Ia density.

Genetic and temporal control of neonatal antibody expression

Two hybridoma cell lines were established with B cells derived from neonatal BALB/c spleen cells. The anti-dinitrophenyl (DNP) antibodies derived from these lines were characterized with respect to their isotype, affinity, and isoelectric point. Antiidiotypic reagents were prepared that permit an analysis of the representation of antibodies sharing idiotype with these two hybridomas in the developing and mature B cell pool of BALB/c mice (Igha) and other murine strains. One of the two antibodies, TF2-36, was found to be indistinguishable from 14% of anti-DNP monoclonal antibodies derived in fragment culture from spleen cells of 1-4-d-old BALB/c donors. B cells expressing this idiotype were found to represent approximately 2% of the anti-DNP-specific repertoire after the 1st wk of neonatal development and into adulthood. The second hybridoma antibody, TF2-76, was found to be expressed at very low levels during the first several days of neonatal development; however, B cells expressing this idiotype increased in frequency during the 2nd wk of neonatal development representing 7% of all DNP-responsive B cells 12-13 d after birth. The proportion of B cells expressing this idiotype also decreased to approximately 2% in adults. The relatively late appearance of B cells bearing this idiotype was confirmed by their susceptibility to tolerance induction after the 1st wk of neonatal development. Both the early neonatal clonotype, TF2-36, and the late neonatal antibody clonotype, TF2-76, were found to be expressed in a similar fashion in F1 mice constructed between Igha and Ighb parentals, but both were expressed at very low levels during the development of Ighb mice. Thus, the control of the magnitude of expression of these neonatal clonotypes appears to be associated with the Igh locus.

A sensitive radioimmunoassay for the detection of monoclonal anti-idiotope antibodies

A radioimmunoassay was developed in order to detect anti-idiotypic antibodies in the supernatants of hybrid cells. This assay is both sensitive and specific for anti-idiotypic (but not anti-allotypic) antibodies. Monoclonal antibodies present in test supernatants are bound by an anti-immunoglobulin coated solid phase. Subsequent incubation with a source of mouse immunoglobulin 'blocks' unreacted anti-immunoglobulin antibodies on the solid phase. Anti-idiotypic antibodies are then detected by their ability to bind 125I-labelled idiotype-bearing antibody. This paper describes the use of this assay to detect monoclonal anti-idiotypic antibodies in 2 systems: the cross-reactive idiotype of A/J anti-ABA antibodies, and the idiotype expressed by the myeloma protein HOPC 8. Similarly, 125I-labelled anti-idiotype antibodies may be used in this assay to detect monoclonal idiotype-bearing antibodies. Further modifications are described which would allow the detection of monoclonal anti-allotype antibodies.

An idiotypic determinant formed by both immunoglobulin constant and variable regions

Immunoglobulin idiotypes are serologically defined determinants associated with the variable (V) region of antibody molecules (reviewed in refs 1-4). One of the best defined idiotype systems is that borne by the phosphorylcholine (PC)-binding IgA proteins TEPC15 (T15) and HOPC8 (H8). The T15 idiotype, defined by sera raised in A strain mice, or in rabbits, is considered identical to that expressed by the majority of BALB/c anti-PC antibodies. To define the idiotypic determinants (idiotopes) of which the T15 idiotype is comprised, monoclonal anti-T15 antibodies were used here to examine both serum and monoclonal anti-PC antibodies. The latter were found to differ from T15 with respect to the idiotope defined by the monoclonal anti-idiotope antibody, 21A5, in that the '21A5 idiotope' was absent from anti-PC sera; of the monoclonal anti-PC antibodies examined, only those which were both T15+ and of the IgA isotype seemed to express this idiotype fully. This result suggests that not only the V region, but also the constant (C) region, of the immunoglobulin molecule can contribute to the formation of an idiotypic determinant. Isotype-restricted idiotopes may be involved in the regulation of antibody responses of particular classes.

A combined proton and phosphorus-31 nuclear magnetic resonance investigation of the combining site of M603, a phosphocholine-binding myeloma protein

Phosphorus-31 nuclear magnetic resonance (NMR) studies on the two phosphorus nuclei of the phosphonium analogue (Me3P+CH2CH2OPO3(2-)) of phosphocholine are used to monitor the charged subsites in the phosphocholine-binding immunoglobulin A mouse myeloma M603. Comparison of the 270-MHz 1H NMR difference spectrum on addition of either this analogue or phosphocholine to M603 and the almost identical changes in the pKa values of the phosphate groups on binding to M603 confirm that the analogue is a good model for phosphocholine. The pKa of the phosphate groups is decreased by 0.5 unit on binding to M603, which is consistent with the phosphate group being hydrogen bonding to Tyr-33H and Arg-95L, as suggested from the X-ray structure, and also implies that the binding energies for the mono- and dianion are similar. The P+Me3 moiety is used to probe the electrostatic interactions in the choline subsite. Titration of the chemical shift of the phosphonium phosphorus reflects a group on the protein that has a pKa value of less than or equal to 5, which from the refined X-ray structure (D.R. Davies, personal communication) of the site is assigned to Asp-97L. The choline subsite is monitored by using 1H NMR difference spectra, which indicates that the subsite is highly aromatic as expected from the crystal structure that places Trp-107H and Tyr-100L in this subsite. The ring current interactions from these rings can account for the 1H NMR chemical shift data on choline.