The immunoregulatory role of bone marrow. I. Suppression of the induction of antibody responses to T-dependent and T-independent antigens by cells in the bone marrow.

Bone marrow cells (BMC) from normal mice suppressed the in vitro IgM, but not the IgG, antibody (Ab) response of spleen cells. BMC were inhibitory only when added during the first 24 hr of culture, and inhibition was not due to an induced shift in the kinetics of the response. Addition of specifically activated T cells or nonspecific T-cell-replacing factors to normal or T-depleted spleen cell cultures did not abrogate suppression while the response to the T-independent antigen DNP-polymerized flagellin or lipopolysaccharide was also suppressed. BMC did not inhibit background Ab synthesis by normal or primed cells in the absence of antigen and did not inhibit, but stimulated, DNA synthesis in normal spleen cell cultures. In addition, high-avidity Ab synthesis was preferentially suppressed. A possible role for the bone marrow suppressor cell in the induction of B cell tolerance is discussed.     

Characterization of three monoclonal antibodies which induce and modulate superoxide anion generation in guinea pig macrophages

Three monoclonal antibodies (Ab), termed KY 12, KY 22, and KY 25 and raised against guinea pig macrophages, induced superoxide anion (O2-) generation in the cells. Although each monoclonal Ab bound to macrophages, each had a different pattern of binding to other cell types. In response to each of the Ab, the amount of O2- generated by 5 X 10(5) macrophages was between 0.5 and 0.7 nmol/min and was augmented threefold to fivefold by the addition of F(ab')2 fragments of rabbit Abs to mouse Ig. When macrophages were pretreated with soluble immune complexes (I.C.) prior to stimulation by the monoclonal Ab, the O2- generation stimulated by KY 12 or KY 22 was reduced by more than 70%. In contrast, pretreatment of macrophages with I.C. did not reduce O2- generation in response to KY 25. KY 12 and KY 22 stimulated adenyl cyclase activity in macrophages, but KY 25 did not. Pretreatment of the cells with soluble I.C. did not interfere with the enhancing effect of the monoclonal Ab on adenyl cyclase activity. Pretreatment of macrophages with KY 12 reduced by over 60% of subsequent generation of O2- in response to wheat germ agglutinin, I.C., formyl-methionyl-leucyl-phenylalanine, phorbol myristate acetate, KY 22, or KY 25. KY 22 or KY 25 did not suppress the generation of O2- in response to other stimuli. These results suggest that KY 22 and KY 25 activate O2- generation in a manner that differs from that of KY 12. These monoclonal Ab should prove useful in examining the regulation of O2- production.     

In vivo treatment with anti-I-A antibodies: differential effects on Ia antigens and antigen-presenting cell function of spleen cells and epidermal Langerhans cells

The in vivo activation of T cells by a variety of antigens can be inhibited by the administration of anti-I-A antibodies (Ab) at the time of antigen priming. This inhibition can partially be explained by the temporary loss of Ia molecules from Ia-bearing antigen-presenting cells (APC) in the spleen. In this study, the effects of i.p. injected monoclonal Ab specific for I-A glycoproteins of different H-2 haplotypes on Ia antigen expression and APC function of spleen cells and epidermal Langerhans cells were compared. It was found that anti-I-A Ab quickly bound to both spleen cell and Langerhans cell Ia antigens. Although spleen cell Ia antigens were modulated and thus temporarily disappeared, Ia antigen expression by epidermal Langerhans cells was not modulated. In functional studies, the capacity of spleen cells and epidermal cells from anti-I-A Ab treated vs control animals to function as APC for antigen-specific, I-A- or I-E-restricted T cell clones was tested. A single injection of anti-I-A Ab completely abolished the APC function of spleen cells as shown in several inbred mouse strains, F1 animals, and with the use of several different Ab and T cell clones. In contrast, Langerhans cell-dependent APC function of epidermal cells remained completely unaltered. Even multiple injections of high doses of Ab never caused any inhibition of Langerhans cell function. Experiments with anti-I-Ak or anti-I-Ad Ab in an (H-2k X H-2d)F1 animal showed abrogation of APC function of spleen cells, but again not of Langerhans cells. Thus in vivo anti-I-A Ab administration appears to differentially affect Ia antigen expression and APC function from spleen and epidermis: Ia antigens are modulated from spleen cells but not from epidermis, and APC function disappears in the spleen but not in the epidermis. The abrogation of splenic but not of Langerhans cell APC function with anti-I-A Ab will facilitate the dissection of the relative contributions of Langerhans cells as compared with other APC in the generation of cutaneous immune responses.     

Activation of the production of cytotoxic factors by mouse spleen cells exposed to the combined action of lipopolysaccharide and muramyl dipeptide in vitro

Lipopolysaccharide (LPS) and muramyl dipeptide (MDP) stimulated murine splenocytes in vitro to produce cytotoxic factors (CF) that killed target cells L-929. This effect was synergic at LPS dose of 10 ng/ml and MDP dose of 10 micrograms/ml. CF production started 2 hours after spleen cell activation and was maximum in 6 hours. CF were produced by macrophages as well as by lymphocytes stimulated by LPS, MDP or their combination. However, synergic effect of immunomodulators was registered only if nonfractionated spleen cells were stimulated during 24 hours. Lymphocytes depleted on T cells did not lack the ability to generate CF upon activation. In addition, LPS and MDP activated synergically the production of interleukin-I by spleen cells in vitro.     

Oxidative stress by visible light irradiation suppresses immunoglobulin production in mouse spleen lymphocytes

In this study, we attempted to induce the oxidative stress in mouse spleen lymphocytes with visible light irradiation and examined the effects of lipid peroxidation on immunoglobulin (Ig) production. The spleen lymphocytes were isolated from 8-week-old male balb/c mice and irradiated with 300 W visible light. When the cells were cultured for 72 hr, Ig contents in culture supernatants were decreased gradually by irradiation for over 30 min. The cell viability was also lowered by the irradiation. Intracellular phosphatidylcholine hydroperoxide (PCOOH) levels and thiobarbituric acid-reactive substances (TBARS) values in culture supernatants were measured as indices of lipid peroxidation and we found that Ig production by mouse spleen lymphocytes was suppressed accompanied with the progress of peroxidation of intracellular phospholipids. Cell membrane fluidity was also significantly decreased, but the intracellular Ig level was not changed in the irradiated cells. These results suggest that the peroxidation of intracellular lipids is a cause of the suppression of Ig production by mouse spleen lymphocytes via lowering cell viability and suppressing Ig synthesis and secretion.     

Antigen-induced in vitro inhibition of immune responsiveness

Addition of the dinitrophenyl derivative of the copolymer of d-glutamic acid and d-lysine (DNP-d-GL) or dinitrophenyl bovine γ-globulin (DNP-BGG) to spleen cell cultures specifically inhibited their capacity to produce an anti-DNP plaque-forming cell (PFC) response to the T-independent antigen dinitrophenylated polyacrylamide beads (DNP-PAA) or to the T-dependent antigen TNP-burro erythrocytes. The degree of unresponsiveness was dependent upon the tolerogen concentration and the duration over which the tolerogen was present in the culture. Treatment with rabbit anti-mouse brain antiserum and complement did not alter the induction of unresponsiveness suggesting a state of B-cell tolerance. Culture of spleen cells for 4 days in the absence of antigen led to the appearance of nonspecific suppressor activity which was demonstrable by its effect on the response of fresh spleen cells to antigen. Preculture in the presence of the immunogen DNP-PAA induced both nonspecific and specific suppressor activities. Induction of specific suppressor activity was not prevented by the presence of the tolerogen DNP-D-GL in the culture. The suppressor activity resided in an adherent T-cell population and did not appear to require macrophages for its induction.     

Mechanisms of idiotype suppression. V. Anti-idiotype antibody inhibits early B cell triggering induced by antigen

To investigate the relationship between antigen-mediated B cell commitment and induction of idiotype (id) suppression, anti-id antibody directed against the major id (TEPC-15 idiotype or T15id) of the anti-phosphorylcholine (PC) antibody was added at various time intervals to BALB/c spleen cell cultures stimulated with a T-independent PC antigen, R36a. The suppressive effect of anti-T15id antibody on the anti-PC response was rapidly decreased as addition of the antibody was delayed; when anti-T15id antibody was added 6 hr after the initiation of the cultures, only partial suppression was induced, whereas the addition of anti-id antibody after 24 hr did not result in significant suppression of the anti-PC response when compared with similar cultures treated with mock anti-id antibody. This acquisition of resistance to id suppression was completely inhibited by treatment with either sodium azide or colchicine, as well as at temperatures below 20 degrees C. The induction of resistance to id suppression during the preincubation period was dependent on the presence of an immunogenic level of specific antigen. This antigen-mediated B cell commitment did not appear to require macrophages because preincubation of macrophages with antigen did not affect the sensitivity of the B cells to anti-id antibody. These results support the possibility that anti-id antibody inhibits early B cell triggering, which involves an energy-dependent, epitope-mediated, lateral mobility of antigen receptors possibly followed by repolymerization of microtubules.     

Adsorptive loss of secreted recombinant proteins in transgenic rice cell suspension cultures

Adsorptive loss of human cytotoxic T-lymphocyte antigen 4-immunoglobulin (hCTLA4Ig) in transgenic rice cell suspension cultures was investigated using glass flasks, plastic flasks, disposable vessels, and stainless steel vessels. When hCTLA4Ig was added to the glass flasks containing sterile AA medium, a rapid decrease in the concentration of hCTLA4Ig, independent on pH, was observed resulting in more than 90% of the protein loss within 1 h due to the surface adsorption. When the same experiments were performed on four different types of culture equipments mentioned above, the lowest adsorption level was observed in the plastic flasks and the highest level was observed in the glass flasks. The use of the plastic flasks retarded the adsorptive loss of hCTLA4Ig at the early stage of the protein production. There was a significant increase in the production of hCTLA4Ig when the flasks were coated with bovine serum albumin. However, the spike test of purified hCTLA4Ig at two different concentrations of 15 and 100 mg L⁻¹ in 500-mL spinner flasks confirmed that the amount of hCTLA4Ig adsorbed was dependent on the surface area of the flasks but not on the concentrations. In conclusion, although the protein adsorption affected the total amount of the protein yielded to some extent, it could be regarded as a minor factor in transgenic plant cell cultures with higher titer.     

A study on the immune receptors for polysaccharides from the roots of Astragalus membranaceus, a Chinese medicinal herb

The immunopotentiating effect of the roots of Astragalus membranaceus, a medicinal herb, has been associated with its polysaccharide fractions (Astragalus polysaccharides, APS). We herein demonstrate that APS activates mouse B cells and macrophages, but not T cells, in terms of proliferation or cytokine production. Fluorescence-labeled APS (fl-APS) was able to selectively stain murine B cells, macrophages and a also human tumor cell line, THP-1, as determined in flow cytometric analysis and confocal laser scanning microscopy. The specific binding of APS to B cells and macrophages was competitively inhibited by bacterial lipopolysaccharides. Rabbit-anti-mouse immunoglobulin (Ig) antibody was able to inhibit APS-induced proliferation of, and APS binding to, mouse B cells. Additionally, APS effectively stimulated the proliferation of splenic B cells from C3H/HeJ mice that have a mutated TLR4 molecule incapable of signal transduction. These results indicate that APS activates B cells via membrane Ig in a TLR4-independent manner. Interestingly, macrophages from C3H/HeJ mice were unable to respond to APS stimulation, suggesting a positive involvement of the TLR4 molecule in APS-mediated macrophage activation. Monoclonal Ab against mouse TLR4 partially inhibited APS binding with macrophages, implying direct interaction between APS and TLR4 on cell surface. These results may have important implications for our understanding on the molecular mechanisms of immunopotentiating polysaccharides from medicinal herbs.     

The human LT system. IV. Studies on the large MW LT complex class: association of these molecules with specific antigen binding receptor(s) in vitro.

The present studies demonstrate that a portion of lymphotoxin (LT) cell-lytic activity present in supernatants from: 1) lectin (Con A, PHA) stimulated nonimmune; or 2) antigen (soluble or cellular) stimulated immune human lymphocytes in vitro, is associated with immunoglobulin (Ig) or “Ig-like” receptor molecule(s). This concept was supported by three findings: 1) LT activity in these supernatants was partially inhibited by heterologous anti-human (IgG) Fab′₂ antisera; 2) LT activity present in soluble antigen stimulated immune human lymphocyte supernatants could specifically bind to and be eluted from Sepharose 4B columns to which the specific stimulating antigen was covalently attached; and 3) LT activity present in primary one-way mixed lymphocyte culture (MLC) supernatants could be removed by absorption on the specific stimulator cells. The amount of total LT activity found to be associated with “Ig” in these supernatants was variable, but ranged from 5 to 20% in lectin stimulated cell supernatants to 20 to 50% in antigen or MLC stimulated supernatants. Physical-chemical studies on the molecular weight class of LT molecules having reactivity with anti-Fab′₂ sera, as well as antigen binding capacity, revealed these properties reside in the large (>200,000) MW LT class, termed complex. The nature and biological significance of these “antigen specific” LT complexes, as they relate to mechanisms of cytotoxicity in vitro, will be discussed.     

Macrophage requirements of CR- and CR+ B lymphocytes for antibody production in vitro.

A Sephadex G-10 column coated with antigen-antibody complexes and complement retains complement receptor-bearing (CR+) mouse spleen cells. The effluent is rich in thymus-derived cells (T cells), and contains bone marrow-derived cells (B cells) which carry surface immunoglobulin (Ig), Ir-associated antigen (Ia), and Fc receptors, but no complement receptors (CR-). Although both unfractionated and CR- B cell populations are capable of producing antibody to red cell antigens, they differ in their requirements for the initiation of the response. Unfractionated B cells cooperate with primed as well as unprimed helper T cells; macrophages are required for this cooperation but can be replaced by 2-mercaptoethanol. CR- B cells cooperate with primed but not with unprimed T cells provided macrophages are added to cultures. After addition of culture supernatant from BCG-activated macrophages CR- B cells cooperate with both unprimed and primed T helper cells.     

The suppressive effect of immunization on the proliferative responses of rat T cells in vitro. II. Abrogation of antigen-induced suppression by selective cytotoxic agents.

Rats given large i.v. doses of ovalbumin or sheep erythrocytes manifest suppressed spleen cell responses (3H-thymidine incorporation) to PHA within hours. Removal of glass wool-adherent cells totally restores responsiveness to that of normal nonadherent spleen cell cultures. Carrageenan, selectively toxic for macrophages, partially restores responses of antigen-suppressed spleen cells in culture, suggesting a supportive role for macrophages in the suppression phenomenon. Treatment of donors with low doses of cyclophosphamide (20 to 50 mg/kg) at the time of antigen injection abrogates the ability of their spleen cells to suppress the responses of normal cells to PHA. The low dose of cyclophosphamide required indicates a target other than the B cell or macrophage and suggests the possibility that cyclophosphamide eliminates the suppressor T cell component of the macrophage-T cell complex.     

Enhancement of antigenic potency in vitro and immunogenicity in vivo by coupling the antigen to anti-immunoglobulin

We have examined the effect of targeting an antigen to the immune system, by covalently coupling it to anti-immunoglobulin (Ig), on its efficacy for T cell stimulation in vitro and its immunogenicity for antibody production in vivo. In vitro, we compared the potency (for stimulation of a ferritin-specific T cell line) of free ferritin, ferritin coupled to goat antimouse IgM (heavy (H) chain specific), ferritin coupled to anti-IgG (H and light (L) chain specific), or ferritin coupled to anti-IgA (H chain specific), as well as a mixture of free ferritin plus goat anti-IgG. The ferritin coupled to anti-IgM or to anti-IgG (H + L), which could bind to surface Ig of B cells, stimulated T cell proliferation at concentrations of ferritin at least 10-fold lower than those required for the other forms of the antigen over the entire time course of the response, with 1000 rad-irradiated spleen cells as presenting cells. Because the goat antibodies were all of the same IgG isotype and coupling ratio, the failure of goat anti-IgA to enhance potency served as a control to exclude Fc receptor binding as the mechanism. The effect was not due to the nonspecific activation of B cells to become more efficient antigen-presenting cells, because mixtures of ferritin plus anti-IgG (H + L) had no effect, and the anti-IgG coupled to ferritin did not enhance presentation of myoglobin to a myoglobin-specific T cell line. The enhanced presentation of ferritin conjugated to goat anti-IgG (H + L) or to anti-IgM was sensitive to radiation doses greater than 2000 R, and was effective at less than one-tenth the number of spleen cells, consistent with the predominance of B cells as antigen-presenting cells for this form of the antigen rather than macrophages and dendritic cells only. When B cells and accessory cells were purified from T-depleted spleen cells, only the B cell preparation but not the accessory cell population manifested enhanced presentation of ferritin coupled to anti-IgG compared with free ferritin, and it was radiosensitive. Finally, allogeneic B cells could not mediate the enhancement in the presence of syngeneic splenic accessory cells (SAC); therefore, the enhancement was not due to shedding of immune complexes from B cells and subsequent presentation by SAC. We conclude that targeting the antigen to B cells as presenting cells greatly enhances its efficacy in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)     

Regulation of helper cell activity by specifically adsorbable T lymphocytes.

Mice immunized with soluble proteins such as human serum albumin (HSA) or ovalbumin (OA) develop in their spleens antigen-specific T and B lymphocytes. These populations of lymphocytes can be separated from each other by different means; e.g. treatment with anti-theta-antiserum and complement removes selectively T lymphocytes, whereas passage through glass bead columns coated with mouse immunoglobulin (Ig): anti-Ig complexes creates a relatively pure population of T lymphocytes. During the course of such separation studies it was observed that the helper capacity of HSA (or OA) immune mouse spleen cells after Ig:anti-Ig column passage frequently was higher than expected from the enrichment in theta-positive cells. In addition, after adsorption onto antigen coated Bio-Gel beads this effect was even more pronounced, i.e., and increase in the relative helper capacity of about 3 or 4 times compared with an increase in the content of theta-positive cells from about 30% to 40 to 50% after adsorption. The present results will demonstrate that the increased helper capacity was a specific phenomenon which was regulated by theta-positive cells. The regulatory cells specifically adsorbed onto antigen-coated Bio-Gel beads have not been successfully eluted by EDTA or excess-free antigen so far, and they were still adsorbed after pre-incubation with anti-Ig antibodies under conditions where specific B lymphocyte adsorption was almost prevented.     

Plasmablast and plasma cell production and distribution in trout immune tissues

These studies describe the in vitro and ex vivo generation of plasmablasts and plasma cells in trout (Oncorhynchus mykiss) peripheral blood and splenic and anterior kidney tissues. Cells were derived either from naive trout and cultured with the polyclonal activator, Escherichia coli LPS, or from trout that had been immunized with trinitrophenyl-keyhole limpet hemocyanin. Hydroxyurea was used to resolve populations of replicating (plasmablast) and nonreplicating (plasma cell) Ab-secreting cells (ASC). Complete inhibition of Ig secretion was only observed within the PBL. Both anterior kidney and splenic lymphocytes possessed a subset of ASCs that were hydroxyurea resistant. Thus, in vitro production of plasma cells appears to be restricted to the latter two tissues, whereas peripheral blood is exclusively restricted to the production of plasmablasts. After immunization with trinitrophenyl-keyhole limpet hemocyanin, specific ASC could be isolated from all immune organs; however, the anterior kidney contained 98% of all ASC. Late in the response (>10 wk), anterior kidney ASC secreted specific Ab for at least 15 days in culture, indicating that they were long-lived plasma cells. Cells from spleen and peripheral blood lost all capacity to secrete specific Ab in the absence of Ag. Late in the Ab response, high serum titer levels are solely the result of Ig secretion from anterior kidney plasma cells.     

Antigen presentation by hapten-specific B lymphocytes. II. Specificity and properties of antigen-presenting B lymphocytes, and function of immunoglobulin receptors

The studies described in this paper were designed to examine the ability of hapten-binding murine B lymphocytes to present hapten-protein conjugates to protein antigen-specific, Ia-restricted T cell hybridomas. BALB/c B cells specific for TNP or FITC presented hapten-modified proteins (TNP-G1 phi, TNP-OVA, or FITC-OVA) to the relevant T cell hybridomas at concentrations below 0.1 microgram/ml. Effective presentation of the same antigens by B lymphocyte-depleted splenocytes, and of unmodified proteins by either hapten-binding B cells or Ig spleen cells, required about 10(3)-to 10(4)-fold higher concentrations of antigen. The use of two different haptens and two carrier proteins showed that this extremely efficient presentation of antigen was highly specific, with hapten specificity being a property of the B cells and carrier specificity of the responding T cells. The presentation of hapten-proteins by hapten-binding B lymphocytes was radiosensitive and was not affected by the depletion of plastic-adherent cells, suggesting that conventional APCs (macrophages or dendritic cells) are not required in this phenomenon. Antigen-pulsing and antibody-blocking experiments showed that this hapten-specific antigen presentation required initial binding of antigen to surface Ig receptors. Moreover, linked recognition of hapten and carrier determinants was required, but these recognition events could be temporally separated. Finally, an antigen-processing step was found to be necessary, and this step was disrupted by ionizing radiation. These data suggest a role for B cell surface Ig in providing a specific high-affinity receptor to allow efficient uptake or focusing of antigen for its subsequent processing and presentation to T lymphocytes.     

Characterization of chimeric antibody producing CHO cells in the course of dihydrofolate reductase-mediated gene amplification and their stability in the absence of selective pressure

Recombinant Chinese hamster ovary (CHO) cells expressing a high-level of chimeric antibody against S surface antigen of hepatitis B virus were obtained by co-transfection of heavy and light chain cDNA expression vectors into dihydrofolate reductase (dhfr)-deficient CHO cells and subsequent gene amplification in medium containing stepwise increments in methotrexate (MTX) level such as 0.02, 0.08, 0.32, 1.0, and 4.0 microM. The highest producer (HP) subclone was isolated from each MTX level and was characterized with respect to cell growth and antibody production in the corresponding level of MTX. The specific growth rate of the HP subclone was inversely proportional to the MTX level. On the other hand, its specific antibody productivity (qAb) rapidly increased with increasing MTX level up to 0.08 microM, and thereafter, it gradually increased to 20 microg/10(6) cells/day at 4 microM MTX. Southern blot analysis showed that the enhanced qAb at higher MTX level resulted from immunoglobulin (Ig) gene amplification. The stability of the HP subclones isolated at 0.02, 0.08, 0.32, and 1.0 microM MTX in regard to antibody production was investigated during long-term culture in the absence of MTX. The qAb of all subclones significantly decreased during the culture. However, the relative extent of decrease in qAb was variable among the subclones. The HP subclone isolated at 1 microM MTX was most stable and could retain 59% of the initial qAb after 80 days of cultivation. Southern blot analysis showed that this decrease in qAb of the subclones resulted mainly from the loss of Ig gene copies during long-term culture. Despite the decreased qAb, the HP subclone isolated at 1 microM MTX could maintain high volumetric antibody productivity over three months because of improved cell growth rate during long-term culture.     

In vivo treatment with monoclonal anti-I-A antibodies: disappearance of splenic antigen-presenting cell function concomitant with modulation of splenic cell surface I-A and I-E antigens

A single injection of anti-I-Ak antibody (AB) into H-2k mice resulted in abrogation of splenic antigen-presenting cell (APC) function for protein antigen-primed T cells or alloantigen-specific T cells. Spleen cells from anti-I-A-treated mice are not inhibitory in cell mixing experiments when using cloned antigen-specific T cells as indicator cells, thus excluding a role for suppressor cells in the observed defect. Also, nonspecific toxic effects and carry-over of blocking Ab were excluded as causes for the defect. Experiments with anti-I-Ak Ab in (H-2b X H-2k)F1 mice showed abrogation of APC function for T cells specific for both parental I-A haplotypes. In homozygous H-2k mice, anti-I-Ak treatment not only abrogated APC function for I-Ak-restricted cloned T cells but also for I-AekE alpha k-restricted cloned T cells. FACS analysis of spleen cells from anti-I-Ak-treated (H-2b X H-2k)F1 mice revealed the disappearance of all Ia antigens (both I-A and I-E determined), whereas the number of IgM-bearing cells was unaffected. The reappearance of APC function with time after injection was correlated with the reappearance of I-A and I-E antigen expression. In vitro incubation of spleen cells from anti-I-A-treated mice led to the reappearance of Ia antigen expression and APC function within 8 hr. Thus, it appears that B cells (as determined by FACS analysis) and APC (as determined by functional analysis) behave similarly in response to in vivo anti-I-A Ab treatment. We interpret these findings as suggesting that in vivo anti-I-A treatment temporarily reduces the expression of Ia molecules through co-modulation on all Ia-bearing spleen cells, thereby rendering them incompetent as APC. Such modulation of Ia molecules does not occur when spleen cells are incubated in vitro with anti-I-A antibodies. These results imply that a primary defect purely at the level of APC in anti-I-A-treated mice may be responsible for the observed T cell nonresponsiveness when such mice are subsequently primed with antigen.     

Suppression of rabbit lymphocyte functions by antibodies specific for allotypic membrane determinants

Regulation of immunoglobulin synthesis and secretion was analyzed by exposing spleen cells of b4b4 rabbits to anti-b4 for 24 hr in culture. As noted previously, no lymphocytes with membrane-bound b4 were found immediately after pulse treatment, but substantial regeneration of membrane Ig (mIg) occurred on further culture in antibody-free medium. Splenocytes cultured either in the presence or absence of anti-b4 showed a marked loss of Ig-secreting cells (ISC) after 24 hr in culture but recovered and exhibited peak numbers of ISC on Day 2. However, ISC formation in cultures of antibody-treated cells was significantly suppressed and thereafter declined at a more rapid rate than in control cultures. Polyclonal B cell activators from Nocardia and from gram-negative bacteria stimulated ISC formation in cultures of normal spleen cells, but responsiveness to these activators was depressed following antibody treatment. Antibody-induced suppression of Ig synthesis was attributed to interference with differentiation of B lymphocytes to the secretory stage.