Immune responses in vitro. I. Cellular requirements for the immune response by nonprimed and primed spleen cells in vitro

Protein-specific helper T-lymphocyte formation initiated by dendritic cells

Antibody responses to hapten-polypeptide conjugates require peptide-specific helper T cells. The latter can be primed in tissue culture by providing small numbers of dendritic cells. Primed, irradiated helper T cells then induce B-cell growth and differentiation in the apparent absence of dendritic cells. Both stages of the antibody response--the induction of helper T lymphoblasts by dendritic cells and the delivery of help from T to B cell--occur in discrete cell aggregates that can be isolated by velocity sedimentation. If helper T blasts revert to smaller "memory" lymphocytes, dendritic cells again are needed to initiate the antibody response.

Intercellular junctions between macrophages in the regional lymph node of the rat after injection of large doses of steroids

Intercellular junctions were often found between macrophages in sinuses of regional lymph nodes of the rat after injection of large doses of cholesterol, cortisone acetate, and estrone at the footpad. They were identified by subplasmalemmal densities, 20-50 nm in width, beneath the plasma membranes of apposed macrophages. No distinct filamentous structures were visible in those dense regions. Electron-dense amorphous materials are lined up at the center of the intercellular space in the junctional regions. Some macrophages form clusters with intercellular junctions. No significant difference in the effect of cholesterol, cortisone acetate, and estrone on the number of intercellular junctions between macrophages was found.

Dendritic cells are critical accessory cells for thymus-dependent antibody responses in mouse and in man

We report that dendritic cells (DC) are necessary and potent accessory cells for anti-sheep erythrocyte responses in both mouse and man. In mice, a small number of DC (0.3-1% of the culture) restores the response of B/T-lymphocyte mixtures to that observed in unfractionated spleen. An even lower dose (0.03-0.1% DC) is needed if the T cells have been primed to antigen. Responses are both antigen and T cell dependent. Selective depletion of DC from unfractionated spleen with the monoclonal antibody 33D1 and complement ablates the antibody response. In contrast to DC, purified spleen macrophages are weak or inactive stimulators. However, when mixed with DC, macrophages can increase the yield of antibody-secreting cells about 2-fold. In man, small numbers (0.3-1%) of blood DC stimulate antibody formation in vitro. Purified human monocytes do not stimulate but in low doses (1% of the culture) inhibit the antibody response. Likewise, selective removal of human monocytes with antibody and complement enhances or accelerates the development of antibody-secreting cells. We conclude that DC are required for the development of T-dependent antibody responses by mouse and human lymphocytes in vitro.

Selective inhibition of functional lymphocyte subpopulations by ribavirin

The present studies were designed to examine the effects of ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), a broad-spectrum antiviral agent, on the generation of murine antibody responses in vitro. Whereas primary and secondary sheep erythrocyte-specific, plaque-forming cell responses by normal murine spleen cells were enhanced by low concentrations of ribavirin (1 microgram per culture), they were strongly inhibited by higher concentrations of ribavirin (5 to 10 micrograms per culture). Both phenomena occurred with the greatest magnitude when spleen cells were exposed to ribavirin 48 to 72 h after culture initiation. Enhancement appeared to result from selective interference with suppressor T cells, since ribavirin failed to augment lipopolysaccharide-specific plaque-forming cell responses in T cell-depleted spleen cell cultures but inhibited concanavalin A-induced lymphocyte proliferation and suppressor T cell generation in cultures of normal spleen cells. The immunosuppressive properties of ribavirin were mediated by a direct antiproliferative effect and, at higher concentrations, a cytotoxic effect for B lymphocytes, since the drug inhibited plaque-forming cell responses in T cell-depleted spleen cell cultures, suppressed lipopolysaccharide-induced lymphocyte proliferation and reduced viable spleen cell recoveries.

Isolation and functional characteristics of adherent phagocytic cells from mouse Peyer's patches

Attempts were made to isolate adherent phagocytic cells (macrophages) from mouse Peyer's patch cell suspensions. Cell suspensions prepared by teasing apart the Peyer's patches contained no adherent phagocytic cells. However, if Peyer's patch fragments were treated with collagenase to disrupt the tissue matrix, cells prepared in this way contained a subpopulation of adherent phagocytic cells. These cells comprised only 0.1-0.2% of the total nucleated cell population of the Peyer's patch. Similar cells could also be isolated from the Peyer's patches of germ-free mice, but as judged by their ability to ingest opsonized erythrocytes, these cells were less activated than cells from the Peyer's patches of normal mice. Adherent cells from the Peyer's patches of normal mice could present antigen (ovalbumin) to T cells, and Peyer's patches cell suspensions containing adherent cells could be stimulated in vitro to produce an anti-sheep red blood cell plaque-forming cell response in the absence of 2-mercaptoethanol. These studies show that although the frequency of phagocytic adherent cells is extremely low in Peyer's patches, these cells have functions consistent with that of adherent cells in other lymphoid tissues.

In vitro studies on the immunological memory for antibody response to bovine serum albumin

Immunological memory for T and B cells was studied in an in vitro culture system with spleen cells from mice primed with bovine serum albumin (BSA). Spleen cells taken from mice immunized at various times previously with a single intravenous injection of alum-precipitated (AP) BSA and bacterial endotoxin (ET) were cultured in Marbrook's system with dinitrophenylated (DNP) BSA as the in vitro antigen. In the cultures of spleen cells obtained from mice primed more than 14 days previously an IgG-predominant anti-BSA response was generated. However, no anti-BSA response was observed in the culture of spleen cells taken from mice primed 7 days previously (day 7 spleen cells). The failure of day 7 spleen cells to generate an antibody response in vitro was shown to be attributable to both the lack of B memory cells and the effect of "suppressive" macrophages induced by ET. On the other hand, anti-BSA memory in the spleen of mice primed with AP-BSA plus ET and 2 months later challenged with AP-BSA matured within 7 days and declined rather quickly by 30 days after the challenge. The difference in the time course of the generation of memory between the spleen cells from primary and from secondary immunized mice might be attributable to the difference in the maturation of memory B cells, since the time course of the development of memory T cells after the secondard immunization was similar to that observed after primary immunization.

Thymus-independent anti-DNP antibody responses to DNP-casein and DNP-gelatin

Although studies on the molecular nature of thymus-independent antigens suggested that the polymeric structure with repeated antigenic determinants and slow metabolism are responsible for thymus-independence, we found that anti-DNP antibody responses to DNP-casein and DNP-gelatin were thymus-independent as well as macrophage-independent. These antibody responses were not affected by in vivo treatment with carrageenan or anti-thymocyte serum. In addition, responses of athymic nude mice to both antigens did not show any significant differences when compared with heterologous nu/+ mice. The findings were confirmed by in vitro experiments; non-adherent spleen cells or T cell-depleted spleen cells responded well to both antigens to the same extent as normal spleen cells. Since both casein and gelatin are polyclonal B cell activators and are not presumed to be high polymer or slow-metabolizing substances, we suggest that thymus-independence in many kinds of antibody response should be reconsidered.

Immune suppression in BALB/c mice bearing the plasmacytoma TEPC-183: evidence for normal lymphocyte but defective macrophage function

This paper analyses impairment of the primary immune response of mice bearing the plasmacytoma TEPC-183. Healthy animals and mice bearing the reported non-immunosuppressive tumour MOPC-104E were used as controls. The defect was shown to affect both primary IgG and IgM responses to chicken cells (CRBC) and to be related to tumour size. However, the primary immune depression could be overcome either by increasing the antigen dose or by using Freund's complete adjuvant together with antigen. Secondary responses were also depressed. This depression was more pronounced if the animals was primed after, rather than before, tumour implantation. Further studies involved the measurement of primary immune responses of immunologically deprived syngeneic mice, after they had been reconstituted with cells from normal or tumour-bearing mice. Lymphocyte reconstitution experiments were carried out in mice which had been irradiated with 950R. Various lymphoid preparations from TEPC-183-bearing mice were unable to bring about such restoration. It is concluded that the impairment of the primary immune response of mice bearing the plasmacytoma TEPC-183 is due to a macrophage, rather than a lymphocyte, abnormality. However, none of these transfer studies suggested that positive suppression of primary immune responses was being mediated by cells from TEPC-183-bearing mice.

Strain-dependent cytotoxic effects of endotoxin for mouse peritoneal macrophages

The cytotoxic effects of bacterial lipopolysaccharides (LPS) on mouse leukocytes have been examined in vivo and in vitro. Intraperitoneal injection of LPS into C57BL/6 mice greatly reduced the recovery of mononuclear cells; LPS was cytotoxic for macrophages, but had a mitogenic effect on lymphocytes. Similar effects of LPS on peritoneal leukocytes were observed in vitro. When monolayers of adherent peritoneal cells were studied in vitro, cytotoxicity was also observed, suggesting that the effect of LPS on macrophages is direct and does not require participation by lymphocytes. Entirely different results were obtained when peritoneal macrophages from LPS-resistant C3H/HeJ mice were studied. LPS failed to activate lymphocytes and was not cytotoxic for macrophages in vitro or in vivo. The effect of LPS on polymorphonuclear leukocytes appeared to be the same in all mouse stains studied. Lipid A was shown to be the most biologically active portion of the LPS molecule. Whereas polysaccharide-deficient endotoxins extracted from rough mutants of Salmonella typhimurium were cytotoxic for macrophages in vitro, polysaccharides that lacked esterified fatty acids did not exhibit this activity. Since LPS may mediate its effects through affinity for mammalian cell membranes, the cellular unresponsiveness of C3H/H3J mice to LPS may reflect an inability of cells from LPS-resistant strains to interact with LPS at the membrane level.

Mitogenic activity of bacterial lipopolysaccharides in vivo: morphological and functinal characterization of responding cells

The in vivo effect of bacterial lipopolysaccharides (LPS) on mouse spleen cell subpopulations was investigated. Intravenous administration of LPS resulted in marked enlargement of the spleen, accompanied by increased cellular proliferation and enhanced nucleated cell recoveries. At least two morphologically distinct cell types appeared to be targets for LPS. Polymorphonuclear leukocytes accumulated rapidly with a relatively minor degree of cell division. In contrast, a substantial proportion of splenic lymphocytes transformed into large lymphocytes and blast cells which actively incorporated [3H]thymidine. Proliferating cells were identified as bone marrow-derived (B) lymphocytes by their ability to form C3-dependent rosettes and to synthesize immunoglobulin. These cellular responses were not antigenically induced, since LPS derived from mutants lacking the polysaccharide moiety gave similar results. Thus, splenic B lymphocytes appear to interact and respond to LPS in vivo in the same manner as observed in vitro. These data suggest that the capacity of LPS to directly activate B lymphocytes, initiate cellular proliferation, and induce immunoglobulin production by bone marrow-derived cells in vivo may contribute to its adjuvant activity.

A miniaturized in vitro diffusion culture system

A miniaturized diffusion culture apparatus holding 24 individual cultures and utilizing 1/10 the cells and volume of standard Marbrook-type cultures is described. This system was evaluated by studying the anti-sheep erythrocyte response of spleen cells from unprimed or primed and boosted mice. Compared to parallel Mishell--Dutton plate cultures memory responses in mini-diffusion cultures rise more slowly, peak 1--2 days later and thereafter decline less rapidly. Moreover, the diffusion cultures give a pronounced IgG response peaking at 6 days, while the abortive IgG response evident in plate cultures at 4 days rapidly disappears. While viability in the two systems is equivalent, cell recovery on days 7 and 8 is markedly higher in the diffusion cultures. Of 4 cell concentrations tested, 2 million cells are found to produce the optimum anti-sheep erythrocyte plaque-forming cell response. A 0.2 micron nucleopore membrane is preferable to a dialysis membrane and yields up to a 2-fold higher response. Replacement of the reservoir medium on day 4 impairs rather than improves the response. The culture system was also found to support an excellent primary response. This response is dependent on the presence of 2-mercaptoethanol and does not require rocking.

Conditions for the development of IgM- and IgG-antibody-secreting cells from primed mouse splenocytes in vitro

A modified Marbrook chamber has been devised and manufactured which will fit inside a standard tissue culture Petri dish. A comparison has been made between Mishell-Dutton and modified Marbrook culture systems with respect to their ability to support an immune response by quiescent memory cells exposed to antigen in vitro. Good culture conditions are maintained for considerably longer in the modified Marbrook cultures and it seems that as a consequence these cultures support a large and reliable IgG response, normally absent or very small in cultures of the Mishell-Dutton type. Ease of manipulation and convenient size make the modified Marbrook system a good prospect for future long-term experiments.

B-memory cells can be stimulated by antigen in vitro to become IgG antibody-secreting cells

Whereas DNP-KLH primed mouse spleen cells fail to show the high IgG anti DNP levels characteristic of an anamnestic immune response when cultured for 5 days under Mishell-Dutton conditions, we show here that such a response can be observed after 8--10 days in vitro using modified Marbrook culture vessels. The kinetics of this secondary response in vitro resemble that described elsewhere for the adotpive secondary immune response in irradiated recipients, and show that insignificant numbers of IgG PFC can be expected before 6 days of culture. This timing is governed by the maturation state of B cells at the start of culture, and was not accelerated by the addition of recently boosted carrier primed spleen cells. We conclude that the deficit in IgG PFC numbers that characterizes Mishell-Dutton cultures of cells primed 2--4 months previously is due to the shortage of time during which such cultures can maintain lymphocyte division and maturation.

Regulatory mechanisms in cell-mediated immune responses. IV. Expression of a receptor for mixed lymphocyte reaction suppressor factor on activated T lymphocytes

Suppression of the mixed lymphocyte reaction (MLR) by a soluble factor produced by alloantigen-activated spleen cells requires genetic homology between the factor-producing cells and responder cells in MLR. The ability of lymphocytes used as MLR responder cells to adsorb MLR suppressor factor was tested to investigate the expression of a receptor structure for suppressor molecules. Normal spleen or thymus cells had no effect on suppressor activity. Concanavalin A (Con A)-activated thymocytes, however, effectively removed suppressor activity, suggesting that the receptor is expressed only after activation and is not present or not functional on resting cells. Significantly neither phytohemagglutinin- nor lipopolysaccharide-activated lymphoid cells absorbed the factor. Furthermore, only Con A-activated thymocytes demonstrating genetic homology with the cell producing suppressor factor for H-2 regions to the right of I-E were effective absorbants. Alloantigen-stimulated spleen cells syngeneic to the suppressor cell also removed suppressor activity. These data support an hypothesis that subsequent to stimulation in MLR, T lymphocytes express a receptor, either through synthesis or alteration of an existing molecular structure, which then provides the appropriate site for interaction with suppressor molecules.

Interferon: effects on the immune response and the mechanism of activation of the cellular response

The discovery of interferon in 1957 by Drs. Isaacs and Lindenmann led to major revisions in the concepts of man's defenses against viral infections. There are at least two types of interferon. Along with their antiviral properties, they have recently been shown to exert a suppressive effect on the humoral and cellular immune response; they affect both B and T lymphocytes. A variety of substances, including virus, polyribonucleotides, and mitogens for T lymphocytes, are good interferon inducers. T lymphocytes seem to be necessary for these inducers to exert their immunosuppressive effects. The immunosuppressive effects of interferon inducers suggests that interferons may be mediators of suppressor T lymphocyte effects. In the virus system, interferon does not exert its antiviral effects by direct action on the virus, but rather derepresses a cell gene that results in the production of an antiviral protein. This antiviral protein is probably the mediator of inhibition of virus replication. This is a complex sequence of events that results in the interaction of interferon with the cell membrane and the resulting production of the antiviral state in the cell. This review will examine the various steps of this involved process.

The T cell-dependent period of the immune response to sheep erythrocytes

To study the T cell-dependent period of the immune response of mouse spleen cells to sheep erythrocytes the co-operation between T and B cells was abrogated at different times during the in vivo or the in vitro response. The abrogation was performed by killing the T cells with anti-theta serum or anti-H-2 serum. The surviving cells were subsequently cultured in vitro and the number of IgM plaque-forming cells was determined each day. The results indicate that T cells play an important role during the first 3 days of the response in vivo. However, during the in vitro response the presence of the T cells is only required during the first 2 days. The difference between the response in vivo and in vitro is probably due to a synchronous start of the plasma cell development in vitro and a more asynchronous start of this process in vivo.

B cell tolerance induced by polymeric antigens. II. Effects of tolerance on hapten-binding lymphocyte levels in primary and secondary antibody responses

Tolerogenic doses of hapten [2,4-dinitrophenyl (DNP)]-coupled type 3 pneumococcal polysaccharide (DNP-lys2.5-S3) totally abolished the anti-DNP rosette-forming cell (RFC) response to primary immunization with DNP-hemocyanin in mice, while lightly substituted antigen (DNP-lys0.6-S3) had little effect. Both antigens suppressed secondary anti-DNP RFC responses to DNP-KLH. Limiting doses of DNP-lys-S3 preferentially suppressed antibody-secreting cell levels, and had less effect on RFC. DNP-lys2.5-S3 was 500--1000-fold more potent in "blockading" primary RFC in vitro than DNP-lys0.6-S3, whereas both antigens were equally effective in blocking secondary RFC. These results suggest that the sensitivity of primed B lymphocytes to inactivation by DNP-lys-S3 is related to their high avidity for antigen. Furthermore, this appears to be largely due to a high density of immunoglobulin receptors on primed cells since the affinities of primary and secondary RFC for monovalent hapten were indistinguishable. Treatment of primarily immunized mice with DNP-lys2.5-S3 2 h before assay abolished 90% of RFC. Therefore, the reduction in RFC levels in tolerant mice may be due to cellular blockade by persisting tolerogen. However, it seems unlikely that simple blockade of antigen-reactive cells is the sole mechanism operative in this system.

IgG response in vitro. I. The requirement for an intermediate responsive cell type

We have studied a secondary IgG anti-dinitrophenyl response in dissociated mouse spleen cell cultures which is comparable in magnitude to the responses detected after adoptive transfer. The data indicate that the responsive precursor cell is not a recirculating memory cell but is an intermediate B cell type which appears in vivo after antigen challenge of primed mice. Both antigen and T helper cells are required for in vitro stimulation of the intermediate cell type into the division and maturation steps leading to IgG antibody secretion. The buoyant density of precursor cells has been analyzed by bovine serum albumin density gradient centrifugation, and is consistent with their recent origin by division from memory cells.

Antibody response to phosphorylcholine in vitro. I. Studies on the frequency of precursor cells, average clone size and cellular cooperation

The anti-phosphorylcholine (PC) antibodies synthesized by BALB/c spleen cells in microcultures upon immunization with heat-killed vaccine of Pneumococci R36A (Pn) are directed exclusively to the PC epitope. These antibodies are of very restricted avidity and 88% of the responding clones express the idiotype characteristic of the TEPC-15 PC-binding myeloma. This idiotypic restriction appears to be due to the absence of clones capable of expressing other idiotypes, rather than to "clonal dominance". The estimated frequency of precursor cells for the PC epitope is 1 X 10(-5) to 2.5 X 10(-5). These precursors give rise to clones with an average size of 9 plaque-forming cells. When the logarithm of the number of negative wells was plotted against the number of spleen cells/well, the fraction of nonresponding cultures decreased exponentially as the number of spleen cells was increased. This indicated that only one cell type was limiting in our assay, presumably a B cell. Furthermore, treatment of spleen cells with AKR anti serum completely abolished the response to sheep red cells without affecting the response to PC. It is concluded that PC is a T cell-independent antigen. Of interest was the finding that PC requires adherent (A) cells and this is a particular characteristic of PC, since most T cell-independent antigens have been found not to require A cells. Reasons for the possible homogeneity of the response to PC are also discussed.

Activation of T and B lymphocytes in vitro. I. Regulatory influence of bacterial lipopolysaccharide (LPS) on specific T-cell helper function

The present studies were undertaken to analyze the nature of the effect of bacterial lipopolysaccharide (LPS) on antibody production in vitro. We have done this by making comparative studies of the effects of LPS on in vitro primary and secondary antibody responses to soluble hapten-protein conjugates and to particulate and soluble sheep erythrocyte antigens. The results obtained demonstrate that the biological action of LPS in vitro may be predominantly manifested on the function of B lymphocytes or T lymphocytes depending on the conditions employed. In the absence of antigen, LPS appears to act primarily on B lymphocytes. In the presence of antigen, however, the data presented here show that LPS significantly influences specific helper T-cell function and it is this latter influence that is predominantly responsible for the adjuvant effects of LPS on antigen-specific antibody responses.

Identification of a novel cell type in peripheral lymphoid organs of mice. I. Morphology, quantitation, tissue distribution

A novel cell type has been identified in adherent cell populations prepared from mouse peripheral lymphoid organs (spleen, lymph node, Peyer's patch). Though present in small numbers (0.1-1.6% of the total nucleated cells) the cells have distinct morphological features. The nucleus is large, retractile, contorted in shape, and contains small nucleoli (usually two). The abundant cytoplasm is arranged in processes of varying length and width and contains many large spherical mitochondria. In the living state, the cells undergo characteristic movements, and unlike macrophages, do not appear to engage in active endocytosis. The term, dendritic cell, is proposed for this novel cell type.

Critical role of determinant presentation in the induction of specific responses in immunocompetent lymphocytes

A detailed analysis of the role of determinant presentation in the process of triggering immunocompetent lymphocytes has been made utilizing cell-bound hapten-carrier conjugates to elicit secondary antihapten antibody responses, primarily in vitro. The results of these experiments demonstrate that: (a) hapten-protein conjugates will attach to the surface membranes of macrophages directly, in the absence of specific antibodies, in a highly immunogenic form; (b) such macrophage-bound conjugates serve as remarkedly efficient stimuli to trigger both thymus-derived (T) and bone marrow-derived (B) cells in a specific manner, lowering the optimal threshold antigen dose (in molar terms) by several logs as compared with soluble antigen; (c) the macrophage is not unique in this regard, since fibroblasts are essentially comparable in the capacity to present antigen in highly immunogenic form; (d) cell surface-bound antigen clearly favors secondary in vitro responses of the IgG as compared with the IgM antibody class; (e) in terms of triggering B or T cells, antigen bound to macrophages in the form of immune complexes does not appear to possess any appreciable advantage over equimolar quantities of directly attached antigen; (f) the increased immunogenicity of cell-bound antigen appears to reflect certain crucial, and undefined, features of cell surface membranes and not merely the stabilization of determinants on a relatively immobile surface; and (g) although the efficiency of lymphocyte triggering is markedly enhanced by cell-bound antigen, the presence of macrophages is apparently not an absolute requirement for eliciting secondary in vitro antibody responses to soluble hapten-protein conjugates. The relevance of these observations to the nature of the signal induced upon antigen interaction by specific lymphocytes and the sequential cellular events involved in the regulatory influence of activated T cells on B cell responses to antigen is discussed. We postulate that T lymphocytes are best triggered by cell-bound antigen and that after this step the activated T lymphocytes regulate the triggering of B cells with antigen.

Functional maturation of thymic lymphocyte populations in vitro

Mouse thymocytes were cultured for short periods of time either alone or with one of two supporting cell populations, splenic adherent cells or thymic epithelial cells. The thymus-derived (T) cell activity of thymocytes cultured on supporting cell populations increased dramatically during 2 days of culture, as assayed in the mixed lymphocyte interaction (MLI), response to phytomitogens, and helper cell activity in the in vitro antibody response. The level of activity attained was equal to that of spleen and lymph node lymphocytes and greater than that of steroid-resistant thymocytes. The cultured thymocytes had surface antigens characteristic of mature T lymphocytes with regard to theta and H-2. The appearance of functionally active lymphocytes in vitro depended upon cell division. Most of the active cultured cells arose from cells already undergoing maturation, i.e., from cells with reduced theta determinants and increased H-2 determinants. We therefore have generated a population of thymocytes indistinguishable from peripheral T lymphocytes using simple in vitro techniques. The extent to which the production of these active lymphocytes depends upon in vitro differentiation is discussed.

Immune responses in vitro. V. Suppression of M, G, and A plaque-forming cell responses in cultures of primed mouse spleen cells by class-specific antibody to mouse immunoglobulins

Suppression of Ig class-specific PFC responses by class-specific antibody to mouse immunoglobulin was studied in cultures of spleen cells from immunized mice. In contrast to cultures from normal mice where anti-micro suppressed responses in all Ig classes, anti-micro had progressively less suppressive effect on gamma(1) and gamma(2) responses in cultures from immunized mice with time after immunization. This was most pronounced at 10 days after immunization when anti-micro suppressed gammaM and gammaA responses, but had no or slight effect on gamma(1) or gamma(2) responses which were still suppressed with anti-gamma(1) and anti-gamma(2). These changes in precursor cell susceptibility to anti-micro were antigen specific.

Immune responses in vitro. IV. Suppression of primary M, G, and A plaque-forming cell responses in mouse spleen cell cultures by class-specific antibody to mouse immunoglobulins

The suppressive effects of monospecific goat anti-mouse globulins on primary immunoglobulin class-specific plaque-forming cell responses in mouse spleen cell cultures were investigated. Anti-micro suppressed responses in all immunoglobulin classes, whereas anti-gamma(1) and anti-gamma(2) suppressed the gamma(1) and gamma(2) responses but not gammaM or gammaA responses, and anti-gammaA suppressed only gammaA responses. The mechanism of action of the anti-micro was studied in detail because of its suppression of responses in all immunoglobulin classes. The anti-micro was specific for micro-chain determinants; its activity was dose dependent, but was not mediated by killing cells with surface micro-chain determinants. Free gammaM but not gammaG myeloma proteins in solution effectively competed with micro-bearing cells for the anti-micro. An excess of anti-micro was necessary in the cultures for 48 hr to insure complete suppression of 5-day responses. However, after removal of excess anti-micro at 48 hr, responses could be stimulated by newly added antigen in cultures where incubation was prolonged to 7 days. Anti-micro was most effective when added at the initiation of cultures and had no suppressive effect when added at 48 hr. Excess antigen did not effectively compete with anti-micro for antigen receptors. Precursors of antibody-forming cells were shown to be the cell population where the suppressive activity of anti-micro was mediated. The experiments suggest that anti-micro combines with micro-chain determinants in antigen-specific receptors on the surfaces of antibody-forming cell precursors, prevents effective stimulation by antigen and subsequent antibody production. To explain suppression of responses in all Ig classes by anti-micro, several models were proposed. It is not possible to determine from the data whether stimulation of precursor cells with gammaG or gammaA receptors requires concommitant stimulation of separate cells with only gammaM receptors, or whether cells bearing gammaM receptors are precommitted to or differentiate into cells capable of synthesis of other Ig classes, or whether receptors of gammaM and another Ig class are present on some virgin precursors or the second Ig receptor appears after antigenic stimulation.

The requirement for macrophages in the secondary immune response to antigens of small and large size in vitro

Tissue culture techniques were combined with cell separation procedures, antimacrophage serum and soluble and particulate forms of sheep red cell antigen to investigate the cellular requirements for a secondary antibody response. By using the highly efficient active adherence column separation method of Shortman which almost completely removes phagocytic cells, it was found that the secondary response to SRC was macrophage dependent. This conclusion was verified by the use of specific antimacrophage serum and by a combination of both methods. Critical tests were used to verify that these separation methods acted on phagocytic and not on other cells, for example, thymus or bone marrow derived lymphocytes. In contrast, the secondary immune response to POL and solubilized SRC antigen was not dependent on the presence of phagocytic cells, as highly purified lymphocytes responded normally to these antigens. Antimacrophage serum did not depress the immune response to these soluble antigens. These results indicate that the requirement for macrophage activity depends on the physical size of the antigen. These findings, obtained in the secondary response in vitro, were closely analogous to previous findings from this laboratory on the cellular basis of the primary response to SRC and POL. The reasons for the different cellular bases of the secondary immune response to various molecular forms of antigen are discussed. The similar cellular basis of the primary and secondary response in vitro suggests that the basic mechanisms of immunization in these responses are the same.