Induction of immunity and tolerance in vitro by hapten protein conjugates. II. Carrier independence of the response to dinitrophenylated polymerized flagellin

Thymus-independent immunogenicity in vitro of the divalent antigen DNP-polyethylene oxide

Chemically simple and physically well-defined dinitrophenyl derivatives of polyethylene oxide (DNP-PEO) can be prepared in a wide range of forms and sizes. These materials were used to investigate the molecular basis of immunogenicity and the binding of the antigens to membrane-bound receptors. Both di- and multivalent DNP-PEO activate normal murine B lymphocytes to yield primary anti-DNP antibody response in vitro. The immunogenicity is dependent on the carrier chain length but independent of T cells. Responses comparable to those induced by DNP-conjugated polymerized flagellin are induced by divalent linear materials of medium molecular weights of about 60,000. A highly multivalent material is moderately immunogenic, but at much lower antigen doses than divalent materials. The carrier PEO does not affect B-cell responses to DNP-PEO or T-cell response to succinyl concanavalin A. Moreover, it shows no polyclonal mitogenicity at concentrations as high as 1 mg/ml. Studies of antigen binding to cell surface DNP receptors show that the strongly immunogenic materials of medium molecular weights have an appreciable tendency to bind bivalently and thus potentially to crosslink receptors. The binding of smaller, less immunogenic antigen appears predominantly monovalent.

Effect of polyethyleneglycol (PEG) on spontaneous and polymyxin B-induced histamine release from rat peritoneal mast cells

Mast cells were isolated from the peritoneal cavity of rat and purified by centrifugation in a gradient of Percoll. The spontaneous and polymyxin B-induced release of histamine was studied after preincubation of the cells with polyethyleneglycols (PEGs) of different molecular weight (200-20,000 dalton) and with fatty acid derivatives of PEG 6000. It was found that very low concentrations (less than 0.1%) of PEG 6000 reduced the spontaneous and polymyxin B-induced release of histamine to a greater extent than the same concentration of bovine serum albumin. The inhibition increased with the size of the PEGs, but was little affected by the presence of fatty acid ligand bound to PEG.

Dissociation of the anti-hapten and anti-carrier responses of mice injected with dinitrophenylated lipopolysaccharide

The quantitative and qualitative nature of the antibody responses of euthymic (normal, RML) and athymic (nude) mice injected with dinitrophenylated (DNP) lipopolysaccharide (LPS) was evaluated. Antibody responses to both the haptenic (DNP) and carrier (LPS) determinants were measured. On a quantitative basis, RML and nude mice stimulated with DNP-LPS produced only primary anti-DNP responses, whereas both primary and secondary anti-LPS responses were elicited by this conjugate. The failure of DNP-LPS to trigger secondary anti-DNP responses was not dependent on the amount of DNP-LPS given in the primary or secondary doses and could not be overcome by repeated injections of DNP-LPS. Also, the anti-DNP responses of RML mice injected repeatedly with DNP-LPS were restricted to immunoglobulin M antibodies whereas both immunoglobulin M and G anti-LPS responses were elicited. Nude mice also produced immunoglobulin G antibodies to the LPS determinants. These data showed a dissociation of the anti-hapten and anti-carrier antibody responses and suggested that different immunological signals were functioning in the respective anti-DNP and anti-LPS responses.

A chemical approach to the mechanism of B-lymphocyte activation. II. The pure presentation of haptens does not inactivate B lymphocytes

Dinitrophenyl (DNP)-lysine-polymethylmethacrylate and DNP-cellulose conjugates do not irreversibly inactivate anti-DNP antigen-sensitive cells, regardless of the dose (up to 10 mg) or persistence of the stimulation (up to 2 weeks). Since these conjugates constitute pure hapten presentations, it is concluded that the pure hapten presentation to B lymphocyte does not irreversibly inactivate them. When murine spleen cells are cultured with Escherichia coli lipopolysaccharide (LPS) and (non-immunogenic) DNP-lysine-polymethylmethacrylate or (non-immunogenic) DNP-cellulose conjugates, an anti-DNP immune response occurs. However, replacement of DNP-lysine-polymethylmethacrylate with polymethylmethacrylate, or DNP-cellulose with cellulose, also results in a similar anti-DNP response. It is consequently concluded that the anti-DNP responses are entirely elicited by LPS, the hapten Dnp being inoperative. The anti-DNP response elicited by DNP-Ficoll is, upon exhaustive testing, carrier-dependent. This implies that the mechanism of DNP-Ficoll immunogenicity is not two cooperative signals passed on to B lymphocytes via the hapten DNP. These results argue against any two-signal model of B-lymphocyte activation.

Analysis of the role of different cell types in the genetic regulation of antibody production to the thymus-independent synthetic polypeptide poly (DTyr, DGlu)-poly (DPro)--poly (DLys)

The immune response potential of mice to the thymus-independent synthetic polypeptide poly (DTyr, DGlu)-poly(DPro)--poly(DLys)[D(T,G)-Pro--L] is genetically regulated. The defect in the ability of low responder mice to mount an immune response to this antigen appears to be expressed in their B cell population since the presence of thymocytes, or addition of "educated T cells" or supernatant of T cells after stimulation with the antigen neither enhanced, nor suppressed the level of antibodies produced in both low and high responder mice. Low responsiveness could not be enhanced either by stimulation of macrophages or by injection of poly(A) - poly(U) in contrast to the significant effect of these agents on low responses to the thymus-dependent poly(LTyr, LGlu)-poly(LPro)--poly(LLys) [L(T,G)-Pro--L]. These results suggest that macrophages do not participate in the limiting step, or are not involved at all, in antibody production towards the thymus-independent polypeptide. The antibodies produced in response to D(T,G)-Pro--L were found to be mainly of the 7 S class. T cells are not required for the production of mercaptoethanol resistant antibodies to this immunogen since they were found in intact mice as well as in T cell depleted animals.

Requirement for accessory cells in the antibody response to T cell-independent antigens in vitro

The antibody responses of mouse spleen cells in vitro to three thymus-independent (TI) antigens namely, polymeric flagellin (POL) of Salmonella adelaide, DNP-Ficoll and "soluble" sheep erythrocyte (SRBC) antigen, were found to be dependent on adherent accessory cells (A cells) but to a lesser degree than the response to intact SRBC. Evidence for this comes from selective depletion of A cells from spleen cells and reconstitution with A cell-rich populations. Thus, depletion of A cells by adherence on glass resulted in abolition of the response to SRBC leaving the response to POL intact. More thorough removal of A cells by treatment with carbonyl iron powder was required for appreciable reduction of the responses to POL, DNP-Ficoll and "soluble" SRBC. This reduction in responsiveness was not due to poor cell survival after A cell depletion or to the loss of immunocompetent cells since 1) the recoveries of viable cells in all cultures were similar; 2) the contents of theta- and Ig-bearing cells and tritium-labeled POL-binding cells were unaltered after carbonyl iron treatment, and 3) responsiveness was fully restored by the addition of irradiated and anti-theta-treated A cells from the peritoneal cavity or the spleen. Hence, the hitherto A cell independence of TI antigens on which some theories of B cell activation are based is a result of inadequate depletion procedures, and the minimal model for B cell activation must take into account two cell types: B cells and A cells.

The allogeneic bisection of carrier-specific enhancement of monoclonal B-cell responses

The ability of T cells to enhance the response of syngeneic and allogeneic B cells to thymus-dependent hapten-carrier conjugates was analyzed. This analysis was carried out on individual primary B cells in splenic fragment cultures derived from irradiated reconstituted mice. This system has several advantages: (a) the response of the B cells is entirely dependent on carrier priming of the irradiated recipient; (b) this B-cell response can be quantitated in terms of the number of responding cells; and (c) very small B-cell responses can be readily detected and analyzed. The results indicate that the majority of hapten-specific B cells were stimulated in allogeneic and syngeneic recipients only if these recipients were previously carrier primed. The number of B cells responding in carrier-primed allogeneic recipients was 60-70% of that in syngeneic carrier-primed recipients. The antibody-forming cell clones resulting from B cells stimulated in the allogeneic environment produced small amounts of antibody and antibody solely of the IgM immunoglobulin class, while the larger responses in syngeneic recipients were predominantly IgG1 or IgM plus IgG1. The capacity of collaborative interactions between carrier-primed T cells and primary B cells to yield IgG1 antibody-producing clones was shown to be dependent on syngeny between these cells in the H-2 gene complex. It is concluded that: (a) B cells can be triggered by T-dependent antigens to clone formation through collaboration with T cells which differ at the H-2 complex as long as these T cells recognize the antigen; (b) the immunoglobulin class produced by the progeny of stimulated B cells generally depends on the nature of the stimulatory event rather than the nature of the B cell itself; and (c) stimulation to IgG1 production is dependent on syngeny between the collaborating T and B cells probably within the Ir-1A region. The role of the Ia antigens in the formation of IgG1-producing clones is not yet clear; Ia identity could permit IgG1 production or, conversely, nonidentity of Ia could induce all allogeneic interactions which prohibit IgG1 production.

Role of epitope density in the induction of immunity and tolerance with thymus-independent antigens. II. Studies with 2,4-dinitrophenyl conjugates in vivo

The immunogenicity and tolerogenicity of 2,4-dinitrophenyl (DNP) conjugates of levan, type 3 pneumococcal polysaccharide (SIII), dextran B512 and dextran B 1299 with different levels of substitution were assessed in vivo. It was confirmed that, as in vitro, conjugates with low epitope density are solely immunogenic for Bmu cells, whereas higher density conjugates are both immunogenic and tolerogenic according to dosage. The maximal anti-DNP plaque-forming cell responses attainable varied by 2 log10 according to the carrier, being greatest with dextrans and least with SIII. The effect of the carrier on immunogenicity was not attributable to B cells responding to it, as concurrent tolerization by either free polysaccharide or the conjugate itself was without effect. Optimal immunization was succeeded by varying degrees of responsiveness ("exhaustion") which was greatest with the more immunogenic conjugates. In contrast, reduction of tolerizing dose by cyclophosphamide suppression was only a feature of more highly substituted conjugates.

The immunological properties of haptens coupled to thymus-independent carrier molecules. III. The role of the immunogenicity and mitogenicity of the carrier in the induction of primary IgM anti-hapten responses

Hapten (DNP-lys) conjugates of two putatively nonimmunogenic polymers, hyalutonic acid and poly-gamma-D-glutamic acid, induce significant primary IgM anti-DNP responses in C3H mice. Preparations of various immunogenic (Type 3 pneumococcal polysaccharide (SIII), levan, E. coli lipopolysaccharide) and nonimmunogenic (hyaluronic acid and poly-glutamic acid) polymers were tested for their ability to act as polyclonal mitogens in vitro. In serum-containing spleen cell cultures, only lipopolysaccharide stimulated substantial cell proliferation. In serum-free medium, and using high specific activity [3H]thymidine, lipopolysaccharide, levan, SIII and to a lesser degree hyaluronic acid induced significant thymidine incorporation. However, under the latter conditions cell survival and proliferation were much less impressive. There was no apparent correlation between the capacity of various polymers to induce lymphocyte proliferation and their "potency" as carriers for the generation of a primary IgM anti-DNP response. Furthermore while low doses of lipopolysaccharide elicited "polyclonal" antibody formation in vivo, high doses of SIII, levan and hyaluronic acid did not. These results indicate that T cell-independent B cell triggering is dependent on the polymeric nature of the antigen, and that polymers need not be immunogenic or mitogenic to act as carriers for the induction of primary IgM anti-hapten antibody responses.

Inhibition of a T-cell-dependent immune response in vitro by thymoma cell immunoglobulin

Concentrated medium obtained from cultures of a continuous thymus-derived mouse lymphoma cell line (WEHI-22.1) was found to inhibit a T-cell-dependent (antidonkey red blood cell), but not a T-cell-independent (anti-DNP) immune response in vitro. Passage of such a concentrate through an anti-mouse Ig immunoadsorbent column removed its inhibitory activity. It is suggested that the tumor cell Ig can compete with specific normal T-cell Ig in its collaborative function in immune responses. A similar mechanism may account for anergy associated with some human lymphoid neoplasms.

Mechanism of thymus-independent immunocyte triggering. Mitogenic activation of B cells results in specific immune responses

The present experiments were performed in order to analyze the mechanism by which thymus-independent antigens (nonspecific B-cell mitogens) can induce specific immune responses to antigenic determinants present on the same molecule. The hapten NNP was coupled to the B-cell mitogen, lipopolysaccharide (LPS). The conjugate retained full mitogenic activity and bound specifically to NNP-reactive cells. NNP-LPS activated polyclonal as well as specific anti-NNP antibody synthesis, but the optimal concentrations for induction of specific anti-NNP cells were several orders of magnitude lower than the concentrations required for polyclonal activation. These low concentrations failed to activate nonspecific cells, but they induced specific thymus-independent responses of high-avidity NNP-specific cells with the typical kinetics of antigenic responses in vitro. Furthermore, hapten-specific cells were paralyzed by NNP-LPS concentrations that were optimal for induction of polyclonal activation. Specific activation and paralysis could be abolished by free hapten indicating that selective binding of NNP-LPS to hapten-specific cells was responsible for the specificity of the response. However, the triggering signal lacked specificity, since high-avidity specific anti-NNP cells could still be activated by stimulating concentrations of NNP-LPS in the presence of free hapten, even though the Ig receptor combining sites were presumably occupied by NNP. The findings show that B cells with specific Ig receptors for the antigenic determinants on mitogen molecules preferentially bind these molecules and become activated at concentrations still unsufficient to trigger other B cells that lack specific receptors. It is suggested that activation for primary IgM responses in B cells is the result of "one nonspecific signal." This nonspecific signal is provided by the mitogenic properties of some antigens (highly thymus independent or, alternatively, by nonspecific T-cell factors (for highly T cell-dependent antigens), or both, and the surface structures responsible for triggering are not the Ig receptors. The specific Ig receptors only act as passive focusing devices for nonspecific stimuli, entitling the cell to be selectively activated, even though both the signal and the receptors for the triggering are nonspecific.

Induction of B cell tolerance in vitro to 2,4-dinitrophenyl coupled to a copolymer of D-glutamic acid and D-lysine (DNP-D-GL)

Spleen cells from CBA or congenitally athymic ("nude") mice were pretreated with various concentrations of DNP coupled to a copolymer of D-glutamic acid and D-lysine (DNP(37)-D-GL), under various conditions of time and temperature. After washing, they were then cultured for 3 days with the direct B cell immunogen, DNP coupled to Salmonella adelaide flagella (DNP-FLA). Under all circumstances tried, exposure of cells to 1 microg/ml DNP-D-GL caused a 70-100% depression in the subsequent DNP-specific PFC response, and 100 ng/ml caused a lesser but still substantial effect. At the concentrations used, DNP-D-GL did not affect irrelevant antibody responses. Though cells from nude mice responded somewhat less well to DNP-FLA than those from CBA mice, no significant difference in the reaction of the two populations to the tolerogen was noted. This demonstrates that DNP-D-GL can, as previously suspected, directly cause unresponsiveness in B lymphocytes.

Cell interactions in the immune response in vitro. V. Specific collaboration via complexes of antigen and thymus-derived cell immunoglobulin

The mechanism of interaction of T and B lymphocytes was investigated in an in vitro hapten carrier system using culture chambers with two compartments separated by a cell impermeable nucleopore membrane. Because specific cell interaction occurred efficiently across this membrane, contact of T and B lymphocytes was not essential for cooperation which must have been mediated by a subcellular component or "factor." By using different lymphoid cell populations in the lower culture chamber and activated thymus cells in the upper chamber (with antigen present in both), it was found that the antigen-specific mediator acted indirectly on B cells, through the agency of macrophages. Macrophages which had been cultured in the presence of activated T cells and antigen acquired the capacity to specifically induce antibody responses in B cell-containing lymphoid populations. Trypsinization of these macrophages inhibited their capacity to induce immune responses, indicating that the mediator of cell cooperation is membrane bound. By using antisera to both the haptenic and carrier determinants of the antigen as blocking reagents, it was demonstrated that the whole antigen molecule was present on the surface of macrophages which had been exposed to activated T cells and antigen. Because specifically activated T cells were essential a component of the antigen-specific mediator must be derived from these cells. By using anti-immunoglobulin sera as inhibitors of the binding of the mediator to macrophages, the T cell component was indeed found to contain both kappa- and micro-chains and was thus presumably a T cell-derived immunoglobulin. It was proposed that cell cooperation is mediated by complexes of T cell IgM and antigen, bound to the surface of macrophage-like cells, forming a lattice of appropriately spaced antigenic determinants. B cells become immunized by interacting with this surface. With this mechanism of cell cooperation, the actual pattern of antigen-B cell receptor interactions in immunization would be the same with both thymus-dependent and independent antigens. An essential feature of the proposed mechanism of cell cooperation is that macrophage-B cell interaction must occur at an early stage of the antibody response, a concept which is supported by many lines of evidence. Furthermore this mechanism of cell interaction can be elaborated to explain certain phenomena such as the highly immunogenic macrophage-bound antigen, antigenic competition, the distinction between immunity and tolerance in B lymphocytes, and the possible mediation of tolerance by T lymphocytes.

Induction of immunity and tolerance in vitro by hapten protein conjugates. 3. Hapten inhibition studies of antigen binding to B cells in immunity and tolerance

The capacity of dissociated spleen cell suspensions to be immunized by dinitrophenylated polymeric flagellin (DNP POL), in the absence of thymus-dependent lymphocytes or macrophages, provided a simple experimental system to investigate the mechanism of binding of antigen molecules to nonthymus-dependent lymphocyte (B cell) receptors during the induction of immunity or tolerance. Various nonimmunogenic DNP compounds were used to inhibit the anti-DNP response to DNP POL. By performing inhibition experiments of brief duration at 4 degrees C, it was established that the inhibition of the anti-DNP response by nonimmunogenic compounds was due to competitive blockade of receptors, and not tolerance or receptor modulation. It was found that univalent DNP compounds were much less efficient inhibitors of the antibody response than multivalent DNP conjugates. The difference in inhibitory capacity between univalent and multivalent DNP human globulin (DNP HgG) suggested the importance of interaction with both combining sites of a single receptor antibody molecule. Nonimmunogenic highly conjugated DNP(3)POL was a more efficient inhibitor of the anti-DNP response to immunogenic DNP(1)POL than DNP(12)HgG, indicating that interactions at more than one receptor molecule are involved in immunization of B cells. Recent demonstrations of the rapid metabolic turnover of receptor antibody molecules suggests that the requirement for multipoint binding (to different receptors) may simply be to maintain the antigen at the cell surface in a dynamic system. Competitive inhibition experiments were also performed to investigate the mechanism of binding of DNP(3)POL in the induction of B cell tolerance. It was found that monovalent DNP compounds or multivalent DNP(12)HgG did not prevent the induction of tolerance, unlike their capacity to inhibit immunity, suggesting that a tolerance-inducing antigen binds more avidly to the cell membrane than an immunogen. The inhibition data obtained here, together with prior results describing the differential immunogenicity of DNP conjugates of different structure, and the importance of epitope density on DNP POL conjugates, permit certain conclusions about the details of antigen-receptor interaction in immunity and tolerance. Distinctions between the mechanisms of immune and tolerance induction are discussed.