Allotype Antibodies Research Articles

Allotype Reagents Distinguish Donor and Recipient Antibodies after Hematopoietic Transplantation.

Allogeneic immune responses provide beneficial graft-versus-leukemia (GVL) and detrimental graft-versus-host disease (GVHD). To characterize allogeneic B cells and their antibodies in relation to GVHD and GVL, antigen specific assays are required to distinguish donor and recipient antibodies. Inherited polymorphisms in heavy chain constant regions of immunoglobulin can be recognized by allotype specific monoclonal antibodies. We hypothesize that B cell reconstitution differs after myeloablative and nonmyeloablative (NMA) HCT with clinical implications. To test this, we developed allotype ELISAs to quantify donor and recipient antibody responses for specific infectious and allogeneic antigens. Human sera were screened by ELISA coating monoclonal antibodies specific for human allotypes (IgG1m(f), m(z), m(a), IgG2m(n), and IgG3m(g1)) at titers providing shared dynamic ranges. Pre-transplant sera from 48 patients and their donors were serially diluted, and allotype-specific immunoglobulin was detected by alkaline phosphatase-conjugated polyclonal anti-human IgG. Allotype-null sera clearly segregated from wild-type sera with 10-fold absorbency differences. Each null phenotype was confirmed by total IgG and isotype-specific quantification. Overall, IgG1m(f) was null in 8 of 96 sera (null allele frequency 29%), and IgG2m(n) was null in 23 of 96 (null allele frequency 48%). Six patients were null for both, and overall 17 of 48 donor/recipient transplant pairs were informative for either allotype. Nulls for the remaining three allotypes were infrequently recognized limiting their clinical utility. Additionally, we measured monoclonal IgG1 purified from 5 multiple myeloma patients identifying three null alleles, one wild-type, and a single intermediate polymorphism. Labeled conjugation of the wild-type monoclonal IgG1 enables competitive inhibition analysis of null allotype improving null allotype sensitivity for engraftment less than 5%.Sera were collected monthly from all HCT patients informative for allotype antibody. Three NMA HCT patients who underwent total lymphoid irradiation and anti-thymoglobulin (TLI/ATG) conditioning have donors that are null for IgG2m(n) and are being prospectively assessed for recipient antibody loss. Their recipient allotype-specific IgG persists at pretransplant recipient levels in all three patients measured six months after NMA HCT, and the lead patient expresses 100% pretransplant recipient allotype antibody ten months after HCT. Conversely, a single NMA patient null for IgG2m(n) with a wild-type donor has no detectable IgG2m(n) donor antibodies four months after HCT despite having 100% donor peripheral B cell engraftment measured 30 days after NMA HCT. In contrast, an informative patient undergoing myeloablative HCT developed 25% IgG2m(n) donor specific antibodies 3 months post-transplant, and 50% at 7 months. Others have reported donor allotype specific antibody achieves full engraftment by 6 months after myeloablative HCT (Van Tol et al. Blood 1996). Our ongoing preliminary studies suggest NMA HCT patients experience delayed donor antibody onset and prolonged recipient antibodies as compared to patients undergoing myeloablative HCT. In order to confirm this, we are measuring antigen-specific donor allotype antibody reconstitution for infectious antigens (EBV and tetanus) and allogeneic H-Y antigens.

Identification of chicken Bu-1 alloantigens using the monoclonal antibody AV20

The genetically polymorphic chicken antigen Bu-1 (chB6) has been identified by alloantisera raised against RPL line 6 3 (Bu-1a) and line 7 2 (Bu-1b) birds and subsequently by monoclonal antibodies (mAbs) which identify individual alloantigens. We have produced a monoclonal antibody, AV20, which recognises a monomorphic determinant on the antigen Bu-1. AV20 identifies a marker on both bursal and peripheral B cells. Staining characteristics on bursa, spleen, thymus and peripheral blood lymphocytes are similar to those of the allotypic antibodies which identify Bu-1a and Bu-1b. However, AV20 identified B cells in partially inbred birds as well as inbred lines including line 6 1 and line 7 2, indicating that it recognises a monomorphic determinant. AV20 immunoprecipitated an antigen with a Mw r of 150 kDa under non-reducing conditions and 70–75 kDa under reducing conditions indicating it is a homodimer. Serial immunoprecipitations of bursal-cell lysates from line 6 1 or line 7 2 confirmed that AV20 recognised the same antigen as mAbs against Bu-1a and Bu-1b in the respective lines.

VDJ genes in VHa2 allotype-suppressed rabbits. Limited germline VH gene usage and accumulation of somatic mutations in D regions.

In this study we investigate the molecular genetic basis for VHa- Ig. Knowing that the expression of VHa allotype Ig is suppressed by neonatal injection of rabbits with anti-VHa allotype antibody, and that the decreased level of VHa allotype Ig, VHa+, in the suppressed rabbits is compensated for by an increase in VHa- Ig, we determined the nucleotide sequences of 41 VDJ genes from a2/a2 rabbits neonatally suppressed for the expression of a2 Ig. We compared these nucleotide sequences to each other and identified two groups of VH sequences. We predict that the molecules of each group are encoded by one germline VH gene. Inasmuch as VHa+ Ig is encoded predominantly by one germline VH gene, VH1, it appears that more than 95% of the VDJ repertoire of rabbits may be encoded by as few as three germline VH genes. A genomic VDJ gene whose VH sequence was similar to those of group I molecules was expressed in vitro and was shown by ELISA to encode molecules of the VHa- allotype, y33. Analysis of the D regions in the VDJ gene indicated that germline D2b and D3 gene segments were preferentially used in the VDJ gene rearrangement. A comparison of sequences of D regions of the 41 VDJ gene rearrangements in 3-, 6-, and 9-wk-old rabbits to sequences of germline D gene segments showed an accumulation of mutations in the D region. Inasmuch as we have previously shown that V regions of rabbit VDJ genes are diversified, in part, by somatic gene conversion, it appears now that rabbit VDJ genes diversify by a combination of somatic mutation and somatic gene conversion.

The Expression of IgG Allotypes on Platelets and Immunization to IgG Allotypes in Multitransfused Thrombocytopenic Patients

We investigated whether the platelet-membrane surface carries IgG allotypic antigens and whether these determinants may be important in platelet transfusion therapy. Using a hemagglutination inhibition assay, we showed that the G1m IgG allotypes (a, x, f) and K1m and K3m light-chain allotypes are expressed on the surface of platelets, whereas G3m allotype antigenic determinants were not detectable. In 146 multitransfused thrombocytopenic patients, 35 (24%) patients were found to have antiallotypic antibodies. To study the effect of antiallotypic antibodies on platelet transfusion outcome, patients received platelet transfusions from donors, either positive or negative for the IgG allotype to which patients were immunized. Of the 19 antigen-positive and 19 antigen-negative platelet transfusions given, respectively, the mean platelet count increments at 1 hour were 8,402 +/- 6,402 +/- 6,721 (1 SD) and 9,799 +/- 5,559 (1 SD) P less than .2. Transfusion reactions were not more common when antigen-positive platelet transfusions were given. Despite the presence of IgG allotypic determinants on platelets, allotypic antibodies do not decrease platelet transfusion recovery. Furthermore, passive administration of plasma containing IgG allotypes to patients with antiallotypic antibodies does not lead to innocent bystander-mediated platelet destruction.

The expression of IgG allotypes on platelets and immunization to IgG allotypes in multitransfused thrombocytopenic patients

We investigated whether the platelet-membrane surface carries IgG allotypic antigens and whether these determinants may be important in platelet transfusion therapy. Using a hemagglutination inhibition assay, we showed that the G1m IgG allotypes (a, x, f) and K1m and K3m light-chain allotypes are expressed on the surface of platelets, whereas G3m allotype antigenic determinants were not detectable. In 146 multitransfused thrombocytopenic patients, 35 (24%) patients were found to have antiallotypic antibodies. To study the effect of antiallotypic antibodies on platelet transfusion outcome, patients received platelet transfusions from donors, either positive or negative for the IgG allotype to which patients were immunized. Of the 19 antigen-positive and 19 antigen-negative platelet transfusions given, respectively, the mean platelet count increments at 1 hour were 8,402 +/- 6,402 +/- 6,721 (1 SD) and 9,799 +/- 5,559 (1 SD) P less than .2. Transfusion reactions were not more common when antigen-positive platelet transfusions were given. Despite the presence of IgG allotypic determinants on platelets, allotypic antibodies do not decrease platelet transfusion recovery. Furthermore, passive administration of plasma containing IgG allotypes to patients with antiallotypic antibodies does not lead to innocent bystander-mediated platelet destruction.

An indirect asymmetrical sandwich ELISA using anti-allotype antibodies for the specific and quantitative measurement of mouse IgG2a of Igh-1 b allotype

We recently described an indirect double sandwich ELISA (Klein-Schneegans et al., J. Immunol. Methods (1989) 119, 117) which permits the specific and quantitative measurement of mouse IgM, IgA and IgG subclasses with one major exception: IgG2a of the b allotype (Igh-1 b in mouse strains such as C57BL/6) could not be reliably quantitated even by a very specific and sensitive asymmetrical sandwich ELISA (using two different anti-IgG2a isotype antibodies for capture and for detection). We now describe a similar method based on the use of two different anti-IgG2a allotype antibodies for the capture and detection of IgG2a in the serum of Igh-1 b mouse strains.

DonorIgh-linked genetic control of allotype-specific antibody response

Immunogenicity of allogeneic immunoglobulins in mice were studied, measuring the allotype-specific antibody activity by agglutination of allogeneic antibody-coated red blood cells. It was found that the serum from C.B-20 mice (Ighb, BALB/c-congenic) was uniquely immunogenic in BALB/c mice for allotype antibody response. Whereas the C57BL/6 (Ighb) serum was immunogenic only when heat aggregated and/or combined with adjuvant, the ultracentrifugation-deaggregated C.B-20 serum was definitely immunogenic when administered in a moderate dose (100 microliters/mouse). Even more surprising was the fast that very low doses (0.01-0.1 microliter) of soluble C.B-20 serum, but not C57BL/6 serum, down regulated the allotype-specific response effectively. Genetic analysis on congenic mice suggested that the immunogenicity is controlled by donor Igh or Igh-V (Id-C.B) inasmuch as the serum from BALB/c-congenic C.B-20 (Igh-VbCb), but not BALB/c-congenic BAB/14 (Igh-VaCb), mice was active in BALB/c mice in soluble form. Further studies showed that the Id-C.B was dominantly expressed on the immunoglobulins of (BALB/c x C.B-20)F1 and (C56BL/6 X C.B-20)F1 strains, and was originally derived from the C57BL/Ka strain. The major determinant for the antibody production was encoded in Igh-C, but not in Igh-V. It is suggested that Id-C.B controls the allotype-specific antibody response in an unusual manner, possibly acting as a unique determinant activating helper T cells.

Permanent alteration of the murine Ly-1 B repertoire due to selective depletion of Ly-1 B cells in neonatal animals.

Studies presented here demonstrate that paternal allotype Ly-1 B cells are permanently depleted following neonatal treatment with antibodies to the paternal IgM allotype. Paternal allotype conventional B cells, in contrast, are temporarily depleted by treatment with either anti-IgM or anti-IgD allotype antibodies and return rapidly to normal frequencies once the antibody treatment disappears. These differences are explained by basic developmental differences between Ly-1 B and conventional lineage B cells. That is, the conventional B cell population is replenished from Ig- precursors throughout life and, therefore, is only temporarily affected when depleted in neonates. The Ly-1 B cell population, in contrast, develops from Ig- progenitors during the prenatal and neonatal life but survives because it is exclusively self-replenishing in adults. Therefore, elimination of a population of Ly-1 B cells from neonates is tantamount to removing it forever. These findings suggest that while conventional B cells turn over rapidly and have an effectively unlimited repertoire, Ly-1 B cells express a repertoire whose composition is strongly influenced by neonatal conditions that favor or select against the retention of cells producing certain antibody molecules. Thus, Ly-1 B cells play a unique role in the immune system in that they retain indefinitely the history of the neonatal animal's immunological experience.

In vivo activation of quiescent B cells by anti-immunoglobulin. I. Induction of latent VH allotype production in adult rabbits by treatment with heterologous antibodies or antibody fragments.

We demonstrated previously that injection of adult rabbits with homologous anti-VHa1 allotype antibody induces the appearance in serum of genetically unexpected (latent) a1 immunoglobulin (Ig) and a1-like internal images. We have now investigated the mechanism for this induction effect and have found that treatment of animals with polyclonal goat or monoclonal mouse anti-a1 antibody similarly results in production of unexpected a1 determinants. The N-terminal amino acid sequences of deblocked heavy chains showed that latent a1 Ig induced by monoclonal antibody treatment was identical to nominal a1 Ig at 18 of 19 residues, with the one amino acid difference at position 13 probably due to a single nucleotide change. Like nominal a1, these molecules expressed multiple VHa1 framework epitopes, as demonstrated by direct immunoelectron microscopic visualization of immune complexes. Whereas F(ab)'2 fragments of rabbit anti-a1 antibody retained inducing activity, F(ab) fragments were effective only when administered in an aggregated form; this result suggests that cross-linking of surface Ig receptors plays a critical role in the induction process. We conclude that all rabbits contain dormant B cells expressing germ-line-encoded latent allotypes, and that in vivo administration of anti-Ig antibody causes activation of these cells directly rather than through perturbation of an allotype regulatory network.

Analysis of the hepatobiliary transport of IgA with monoclonal anti-idiotype and anti-allotype antibodies

The processing and fate of mixed immune complexes is influenced by the antibody isotypes present. The hepatobiliary transport of mixed immune complexes containing the mouse IgA myeloma protein J558 and corresponding monoclonal IgG or IgM anti-J558 idiotype or monoclonal IgG anti-mouse IgA allotype antibodies has been studied. The anti-idiotype or anti-allotype antibodies were radiolabeled and injected into mice with or without mouse polymeric IgA (J558). IgG anti-idiotype antibodies to J558 IgA were selectively transported into bile by J558 IgA. This process occurred with a radiolabeled Fab preparation of the IgG anti-idiotype and was inhibitable with IgA of an irrelevant antigenic specificity. Thus, polymeric IgA influenced the fate of IgA-IgG idiotype-anti-idiotype serum immune complexes. A monoclonal anti-idiotype antibody of the IgM isotype (D8-3) was not selectively transported into bile by itself or as an IgA-IgM complex. A monoclonal IgG antibody (CB5-6) to a mouse allotype determinant in the Fc portion of IgA was not selectively transported into bile. This anti-allotype monoclonal antibody inhibited the hepatobiliary transport of 125I-polymeric J558 IgA and therefore appeared to directly or indirectly block the site in the Fc region of IgA recognized by the hepatic receptor.

The role of intercellular contacts in the activation of B lymphocytes by anti-immunoglobulin antibodies.

It has been proposed that anti-Ig antibody activates B cells in a way analogous to the antigens, i.e., it delivers its signal by cross-linking and clustering the Ig receptors on the surface of one cell. However, the cross-linking of different B cells which may deliver to each other a signal has not been considered. Thus, we examined the effect of preventing cell contacts on the response of rabbit B cells to anti-Ig allotype antibody by using a solid agarose medium. First, we examined the 14C-uridine incorporation in liquid medium and in liquid or solid agarose in cultures stimulated with anti-Ig antibody (Ab). The response was high in liquid agarose or liquid medium but was absent when the agarose-containing medium was solidified at the start of the cultures. If the agarose was solidified 6 hr after the start, a good response was obtained. Moreover, if the cells were sedimented at the start before solidifying the agarose-containing medium, a good response was also obtained. Similar results were obtained when T cells were activated by Con A. To examine whether B cells require contacts with other B cells or with non-B cells, we examined their response to anti-Ig Ab in the absence of macrophages or T cells, and found that purified B cells from lymphoid organs or from thoracic duct responded well in the absence of T cells and/or macrophages. The response was also absent when the cells were cultured in agar at a "local" concentration close to 10(8) cell/ml. Also, concentrated supernatants of anti-Ig-stimulated cells did not increase the response to anti-Ig in solid agarose. These two last observations suggest that the lack of response in solid agarose is not due to a lack of diffusible factors or to a lack of feeder cells. Therefore, because the only difference between the cultures that responded to anti-Ig or Con A and those that did not was the distance between the cells, we concluded that the contact between B cells or between T cells is essential to their activation by their respective mitogens. We speculate that the anti-Ig Ab or the antigen cross-links B cells, which then provide each other with the activating signal or with one of the activating signals.

Analysis of the reactivity of four anti-mouse IgM allotype antibodies with mu+ B lineage cells at various stages of differentiation.

We have used two rat monoclonal antibodies (Mab) (Bet-1 and 331.12), a mouse Mab (AF6-78.25), and an alloantiserum (SJA anti-BAB/14) in two-color immunofluorescence analysis and enzyme-linked immunosorbent assays to examine the expression of IgM allotypes at various stages of mouse B cell development, especially at the pre-B cell stage. In agreement with findings previously reported by others, these antibodies displayed the patterns of allotypic reactivity with IgM+ B cells and plasma cells from the appropriate strains of mice: Bet-1 antibody is specific for a allotype, AF6-78.25 and SJA anti-BAB/14 for b allotype, and 331.12 for both a and b allotypes but not e allotype. These antibodies, however, did not react with isolated mu-heavy chains prepared from secreted molecules or synthesized in situ by normal pre-B cells or pre-B cell-derived hybridomas. The requirement of light chain participation in the expression of IgM allotypic determinant(s) was additionally suggested by analysis of a fetal liver-derived hybridoma (F1-26-11) that has been shown to secrete IgM heteromolecules composed of C57BL/6-derived mu-chain and BALB/c-derived kappa-chains. In contrast to the nonreactivity with C57BL/6 mu-only pre-B cell-derived hybridomas, all three antibodies with specificity for the b allotype (AF6-78.25, SJA anti-BAB/14, and 331.12) reacted with this particular hybridoma. After treating surface IgM molecules on B lymphocytes with papain to cleave Fab fragments, the b allotype reactivity of AF6-78.25 mouse Mab, but not 331.12 rat Mab, disappeared, whereas the a allotype reactivities of two rat Mab (Bet-1, 331.12) were not altered. These results suggest that the IgM allotypic epitopes defined by these antibodies appear to be sterically dependent on the assembly of the whole IgM molecules, and rat Mab 331.12 and mouse Mab AF6-78.25 define two separate b allotype specificities, one on the Fc portion and the other on the Fab portion of the IgM molecules, respectively.

Spectrotypic analysis of passively acquired and newly synthesised IgG antibodies in the neonatal and young mouse

Isoelectric focussing with autoradiography has been used to analyse the selective nature of passive transmission of specific anti-Ig allotypic antibodies from the mother to the young mouse, and to study the generation of spectrotypic (clonal) diversity of autologous IgG2a (carrying the paternal inherited Igh-1 b allotype) in BALB/c × SJL/J F1 (Igh-1 ab heterozygote) mice. Transmission of anti-allotypic antibody to neonatal mice was found to be p I restricted, with selection favouring electrophoretically fast IgG. Comparison of the antibody spectrotype in maternal serum, milk and neonatal serum revealed that the p I restriction in transmission operates at the level of the neonatal gut. Analysis of the paternally inherited Igh-1 b IgG2a molecules as they are first synthesised and secreted into the neonatal serum revealed an extensive polyclonality on first detection by the very sensitive focussing assay. it can be deduced that IgV region diversity is generated by IgG2a-synthesising cells prior to, or at the time of, the first secretion of this class of antibody into the serum.

Anti-immunoglobulin antibodies IV. Cross-reaction of anti-idiotypic antibodies specific for rabbit and murine anti-a1 allotype antibodies with Fc fragment of human immunoglobulins.

Anti-idiotype (Id) antibodies against anti-a1 rabbit allotype antibodies were produced in rabbits and mice by immunization with polyclonal rabbit anti-a1 allotype or with a monoclonal murine anti-a1 allotype antibody, respectively. These antibodies recognize an interspecies cross-reactive idiotope on anti-a1 allotype antibodies. However, these anti-Id antibodies also react with various subclasses of human IgG. In multiple systems, it was shown that these anti-Id antibodies interact with the Fc fragment of human IgG and, therefore, exhibit a rheumatoid factor-like activity. These results support the hypothesis that gamma-globulin may not be the only stimulus to clones producing rheumatoid factors and that perhaps other antibodies, especially anti-Id antibodies, also bind gamma-globulin secondarily.

Allotype suppression in the chicken: V. Abnormal isotype ratios of chronically suppressed IgM and IgG allotypes

Chronic allotype suppression was generated in M-1 (Cμ), G-1 (Cγ) heterozygous B14 line chickens either by embryonal injection or by maternal transfer of anti-M-1b allotype antibodies. Using a sensitive radioimmunoassay to detect the suppressed IgM-1b, a striking disparity was observed between the degree of suppression of the IgM-1b allotype and that of the genetically linked IgG-1i allotype. The amount of suppressed IgM-1b ranged between 0.2 and 3% of total serum IgM in chronically suppressed birds. The levels of the genetically linked IgG-1i, however, comprised 5 to 25% of total serum IgG in such birds. The allotypes measured in suppressed chickens were qualitatively identical to those in normal, nonsuppressed birds by serological criteria. These results are discussed within the context of isotype regulation in the chicken.

Induced latent allotypes within rabbit anti‐crossreactive idiotype reagents. Direct immunoelectron microscopic evidence

Immunization of rabbits with anti-VHa allotype antibody leads to the production of an "anti-cross-reactive idiotype (IdX)" reagent which appears to recognize a highly conserved IdX on anti-allotype antibodies. In many rabbits, a large percentage of this "anti-IdX" reagent does not express the nominal VHa framework allotype of the rabbit from which it was derived and is otherwise serologically indistinguishable from the original antigen, i.e. a1 or a2 allotype. To determine whether these anti-IdX molecules were in fact anti-IdX (or internal images) or were induced immunoglobulins bearing latent VHa allotypes, immunoelectron microscopic analysis of the molecules in complex with Fab anti-allotype antibody was conducted. The results show that the complexes do not resemble idiotype-anti-idiotype interactions but are essentially indistinguishable from allotype-anti-allotype complexes. We conclude that a major component of the "anti-idiotype" response of these anti-VHa-immunized rabbits is the production of Ig molecules bearing latent VHa allotypes.

The common idiotypic specificity of anti-a2 allotype antibodies: contribution of H and L chains to idiotype expression

Previously an idiotypic specificity common to anti-a2 allotype Ab from 15 rabbits was detected and characterized. The contribution of H and L chains to the expression of this common idiotypic specificity was determined. Two types of recombinant IgG were prepared: (1) H chains from anti-a2 Ab with L chains from normal a3b4 IgG. and (2) L chains from anti-a2 Ab with H chains from normal a3b4 IgG. By inhibition of binding radioimmunoassay, recombinant IgG having either H or L chains from anti-a2 did not inhibit the binding between anti-a2 Ab and anti-idiotype Ab. By direct binding radioimmunoassay, recombinant IgG of H chains from anti-a2 Ab with L chains from a3b4 IgG reacted with anti-idiotype Ab whereas recombinant IgG with H chains from normal a3b4 IgG and L chains from anti-a2 Ab did not react. These results indicate that the common idiotypic specificity of anti-a2 Ab is determined primarily by the H chain; however, the full expression of the common idiotypic specificity requires the interaction of both H and L chains from anti-a2 Ab.

A predominant idiotype on rabbit anti-VH a1 allotype antibodies: sharing by both major and minor VH subgroups.

In every rabbit examined, greater than or equal to 80% of antibodies directed against the VH allotypic marker, a1, bears a predominant idiotype (IdX-a1). The IdX-a1 marker is site-associated and expressed on H chains, but not L chains, of anti-a1 antibody. Experiments using rabbits suppressed for the VH a subgroup demonstrated that IdX-a1 can be associated with both major (a+) and minor (a-) VH subgroup gene products and that a1 rabbits contain IdX-a1 within their genetic repertoire. The genetic and regulatory implications of our results are discussed.

Monoclonal antibody to an IgD allotype induces a new type of allotype suppression in the mouse.

Studies presented here show that perinatal exposure to anti-IgD allotype antibodies induces a persistant IgG-allotype suppression in the mouse that differs markedly from either the short-term or chronic allotype suppressions induced by antibodies to IgG or IgM allotypes. This novel form of allotype suppression induced by injecting neonatal BALB/c x SJL mice with monoclonal antibody to the paternal Igh-5b (IgD) allotype drastically reduces paternal allotype production during the first 6 mo of the affected animal's life and simultaneously stimulates compensatory production of maternal allotype IgG. In addition, it interferes with the development of B cells carrying the paternal IgD allotype and impairs the development of memory B cells destined to give rise to paternal allotype IgG-producing cells. Thus, its properties make it more like allotype suppression as described in the rabbit than like the known forms of allotype suppression in the mouse. As shown here, Igh-5b-bearing (5b+) B cells are completely depleted from the neonate after anti-5b exposure and only gradually appear as the animal ages. The recovery of the 5b+ population to near normal size (by approximately 14 wk of age) substantially preceeds recovery of the ability to generate normal-size memory B cell populations. Paternal allotype levels in serum remain well below normal until the anti-5b-exposed animals reach approximately 6 mo of age and then climb rapidly, finally stabilizing at levels comparable to levels in controls of the same age. The elevated maternal allotype levels characteristic of the suppression period began falling somewhat earlier and are clearly stabilized within the normal range in 6-mo-old animals. Thus, perinatal exposure to anti-5b compromises B cell development and IgG production throughout early adulthood but has little apparent effect in older animals. Perinatal exposure to antibody to the paternal IgG2a allotype (Igh-1b) or IgM allotype (Igh-6b), in contrast, induces a chronic allotype suppression that has relatively little affect on IgG production in young adults but severely suppresses allotype production in older animals. Furthermore, this type of (chronic) suppression does not influence maternal allotype production and does not interfere with memory B cell development. These differences, illustrated here by data from parallel sets of animals exposed either toi anti-5b or anti-1b, raise a series of intriguing questions concerning the mechanisms regulating B cell development and expression and the nature of the neonatal (B) cell populations with which the suppression-inducing antibodies react.

The turnover of surface immunoglobulins of small lymphocytes and blastic cells

We have previously shown that the maintenance of surface Ig by most B cells in culture is dependent on the continuous presence of polyclonal B-cell activators (PBA). We put forward the hypothesis that lymphocytes shed their surface Ig but replace it only if they are continuously stimulated i.e., that the turnover of surface Ig is a mitogen-dependent process. To demonstrate this hypothesis, rabbit spleen cells were labeled with 125I-Fab anti-light-chain allotype antibody and were incubated in cultures supplemented with normal rabbit serum of an allotype different from that present on the lymphocytes. We found that the surface Ig is released with a half-life of 2 hr whether a PBA was present or not. However, the surface Ig was regenerated only in the presence of the PBA. The decrease in the percentage of cells bearing surface Ig paralleled to a large extent the decrease in the total amount of surface Ig determined by 125I-Fab antibody. The surface Ig of blastic B cells induced in cultures with dextran sulfate had the same half-life of 2 hr, suggesting that the turnover of surface Ig of small and blastic lymphocytes is similar and that it is regulated without any relation to cell activation. The basic phenomena described here and previously for rabbit lymphocytes also occurred when human or mouse lymphoid cell suspensions were used. We concluded that (a) the turnover of surface Ig in vitro is a mitogen-dependent process with a half-life of 2 hr, (b) its regulation is not dependent on cell activation, and (c) it is similar in man, rabbit, and mouse.