Studies on macrophage RNA involved in antibody production

Decisions about dendritic cells: past, present, and future

A properly functioning adaptive immune system signifies the best features of life. It is diverse beyond compare, tolerant without fail, and capable of behaving appropriately with a myriad of infections and other challenges. Dendritic cells are required to explain how this remarkable system is energized and directed. I frame this article in terms of the major decisions that my colleagues and I have made in dendritic cell science and some of the guiding themes at the time the decisions were made. As a result of progress worldwide, there is now evidence of a central role for dendritic cells in initiating antigen-specific immunity and tolerance. The in vivo distribution and development of a previously unrecognized white cell lineage is better understood, as is the importance of dendritic cell maturation to link innate and adaptive immunity in response to many stimuli. Our current focus is on antigen uptake receptors on dendritic cells. These receptors enable experiments involving selective targeting of antigens in situ and new approaches to vaccine design in preclinical and clinical systems.

Protection against pneumococcal infection by a ribosomal preparation

A subcellular extract prepared from nonencapsulated Diplococcus pneumoniae type 3 protected mice against a subsequent challenge with virulent D. pneumoniae types 1, 2, 3, and 7. Potency ratios ranged from 25 (type 3) to >1,175 (type 1). The immunity induced in mice by this preparation was best obtained by intraperitoneal inoculation followed by intravenous challenge. Mice immunized in this manner were protected up to 12 weeks and could withstand a challenge of several hundred LD(50). The protection was destroyed by treatment of the preparation with ribonuclease and was decreased by treatment with protease. The preparation consisted of 60.5% ribonucleic acid, 29.1% protein, 6.3% deoxyribonucleic acid, and 4.0% hexose. Ultracentrifugation studies indicated that this extract had five constituents which are compatible with ribosomal material.

Transfer of tumor specific immunity with "immune" RNA: prospects for the treatment of human cancer

Ribonucleic acids extracted from specifically sensitized lymphoid cells (I-RNA) have been shown to transfer specific immunoreactivity to normal non-immune lymphoid cells. Evidence for the transfer by I-RNA, of immune responses to tumor-associated antigens of animal and human neoplasms, in vivo and in vitro, is reviewed. Results obtained in our laboratory and in other laboratories indicate that xenogeneic, allogeneic and syngeneic I-RNA extracts mediate specific cytotoxicity to tumor cells, in vitro, and mediate transplantation resistance and tumor rejection responses in vivo. Our results suggest that I-RNA preparations fail to elicit immune responses directed against "self" antigens. By contrast, I-RNA's directed against "non-self" tumor-associated antigens appear to induce lymphocytes to effect specific anti-tumor immune responses. The mechanisms responsible for the failure of I-RNA to initiate immune responses against "self" antigens are not known at present and demand investigation. Preliminary results of a clinical Phase I trial of immunotherapy with xenogeneic I-RNA in selected cancer patients are reviewed. I-RNA might offer promise as a new modality for the immunotherapy of human cancer.

Effect of immunization on the RNA polymerase activity of guinea-pig macrophage nuclei

Macrophages from peritoneal exudate contain three types of DNA dependent RNA polymerase. The activity of RNA polymerases in macrophages derived from normal animals is very low. Guinea-pigs were immunized by sheep red blood cells. The immunization enhanced the activity of the RNA polymerase of macrophages derived from peritoneal exudate. The RNA polymerase activity was tested after the solubilization and chromatographic resolution of the three types of polymerases with exogenous template. The results obtained indicated that the immunization enhances the levels of polymerase I and III 10 fold while the level of polymerase II increased 5 fold.

Macrophage-lymphocyte clusters in the immune response to soluble protein antigen in vitro. II. Ultrastructure of clusters formed during the early response

Macrophage-lymphocyte clusters are formed when lymph node cells and autologous peritoneal exudate cells from guinea pigs immunized with tubercle bacilli are cultured in the presence of purified protein derivative of tuberculin (PPD) for 20 h. We have studied the ultrastructure of these clusters employing transmission and scanning electron microscopy. The most simple macrophage-lymphocyte cluster consisted of one macrophage, one large central lymphocyte with a blastoid appearance attached to the macrophage with a broad area of contact, and from a few to more than 20 small peripheral lymphocytes attached to the central lymphocyte by their uropods. Some clusters were of more complex type, containing two or three macrophages or one macrophage with more than one central lymphocyte attached to the surface, but even in these clusters each peripheral lymphocyte was attached only to one central lymphocyte. By morphological criteria the peripheral lymphocytes were T lymphocytes.

Kinetics of macrophages and reticuloendothelial cells in mouse lymph nodes during secondary antibody responses to tetanus toxoid

The proliferative activity and rate of cell renewal of, and incorporation of tritiated nucleosides into, macrophages, reticuloendothelial cells and fibroblasts were studied in lymph nodes of mice before and after a regional second antigenic stimulus with tetanus toxoid. Histological and autoradiographic examinations revealed that in non-stimulated nodes of animals primed 6 months previously, none of the above cell-types was found to synthesize DNA. Throughout a period of 10 days following secondary antigenic stimulation via the hind leg foot pads, only four of approximately five thousand of these cells counted in the popliteal lymph nodes of thirty-four mice were labelled initially by [³H]thymidine. Incorporation of [³H]cytidine could, therefore, be interpreted as reflecting almost exclusively RNA synthesis. Mean grain counts of non-proliferating cells 1 hour after injection of this radioactive precursor started to rise first in small lymphocytes, reached a peak around 6 hours following the booster injection of antigen and returned to slightly elevated values at 12 hours. At this time, the mean labelling intensity of macrophages, reticuloendothelial cells and fibroblasts had barely begun to increase. Peak values for the latter cell-types were attained only on the third day after secondary antigenic stimulation. These findings are interpreted as indicating consecutive waves of enhanced RNA synthesis first in lymphocytes and then in macrophages or the other elements mentioned above. This lends further support to the hypothesis that, following a second injection of tetanus toxoid, elevated rates of RNA synthesis in macrophages are not a prerequisite for triggering lymphocytes to enter proliferation and differentiation. Macrophages having ingested various materials showed significantly higher mean grain counts than cells not containing cytoplasmic inclusions. One early response of the macrophage system to the booster injection of antigen consisted of a more rapid and increased turnover, i.e. replacement of unlabelled by labelled cells with increasing time after injection of [³H]thymidine. The results are discussed in relation to macrophage functions in immune responses and possible cellular transformations in the macrophage series.

Specific inactivation of sensitized lymphocytes in vitro using antigens labelled with astatine-211

This is a study of the use of astatine-211 as an alternative to iodine isotopes in radioactive antigen suicide experiments. The theoretical advantages of ²¹¹At are that it is a high energy (5·87 MeV), short half-life (7·2 hr)α-emitter with a short path length of 60 μm. Its destructive effect, measured in terms of degree of ionization per micron is 300 times that of ¹²⁵I and ¹³¹I. Streptokinase (SK), tuberculin (PPD) and phytohaemagglutinin (PHA) were labelled electrolytically with ²¹¹At (3–9% incorporation). These antigens were not destroyed by the labelling technique or by self-irradiation during radioactive decay. Autoradiography showed that only a small fraction of lymphocytes bound ²¹¹At-labelled SK and PPD whilst most lymphocytes bound ²¹¹At-labelled PHA. Lymphocytes exposed for 40 min to 0·35–1·40 μCi of labelled antigens lost 35–83% of their ability to transform upon subsequent exposure to the unlabelled antigens. The inhibition was specific in that responsiveness to unrelated antigens was retained. These results extend our previous findings with the use of ²¹¹At in in vivo antigen suicide experiments.

Transfer of antigenic macromolecules from macrophages to lymphocytes. I. Autoradiographic and quantitative study of ( 14 C)endotoxin and ( 125 I)haemocyanin transfer

In an in vitro autologous system, studies were carried out on the transfer of either biosynthetically-labelled [¹⁴C]Salmonella enteritidis endotoxin or [¹²⁵I]Maia squinado haemocyanin from macrophages to lymphocytes.

When cultured 1 hour in vitro, lymphocytes adhered to autologous macrophages, forming lymphocyte-macrophage islands (LMI).

Quantitative data obtained from stained thick sections showed that 1.8 per cent of the lymphocytes had adhered to macrophages with ingested [¹⁴C]endotoxin while 0.6 per cent of the lymphocytes adhered to macrophages with ingested [¹²⁵I]haemocyanin. The presence of antigen macromolecules was observed mainly within lymphocytes adhering to macrophages with ingested antigens, i.e. at the level of LMI. On the other hand, autoradiography carried out on the same thick sections, showed that 0.20 per cent of the lymphocyte population in LMI possess silver grains. High resolution autoradiographic pictures of thin sections, showed a peculiar localization of silver grains in LMI lymphocytes: about 80 per cent of the radioactivity was found within lymphocytic nuclei and the remainder either on the cellular membrane or free in the cytoplasm. The disappearance of radioactivity from the LMI-located macrophage membranes (where lymphocytes contain silver grains) as well as the regular inhibition of antigen transfer occurring after pronase treatment of the macrophage which contained ingested antigen, strongly suggest that antigen bound to macrophage membrane was transferred to lymphocytes. As pretreatment of lymphocytes with anti-Ig serum resulted in regular inhibition of antigen transfer, it appears that the Ig receptors of lymphocyte membranes play an important role in the transfer mechanism.

Combined technique, i.e. autoradiography and the peroxidase method for revealing Ig bound to lymphocyte membranes, showed that silver grains occurred only within lymphocytes displaying peroxidase-positive membrane.

The effects of mercaptoethanol and of peritoneal macrophages on the antibody-forming capacity of nonadherent mouse spleen cells in vitro

Nonadherent mouse spleen cells exhibited poor viability and little or no capacity to form antibodies to sheep red cells in the Mishell-Dutton culture system. Viability and antibody-forming capacity could be restored by addition to these cultures of low concentrations of mercaptoethanol (10(-4)-10(-5)M), or by addition of appropriate numbers of mouse peritoneal macrophages. Macrophage concentrations lower than optimal resulted in lower lymphoid cell viability and correspondingly fewer plaque-forming cells, whereas excess macrophages resulted in marked inhibition of antibody formation despite good viability of the lymphocytes. Restoration of the nonadherent cells with mercaptoethanol was thus much simpler and more reproducible than it was with macrophages; furthermore, the number of plaque-forming cells developed in cultures restored with mercaptoethanol was approximately fourfold higher than it was in cultures restored with optimal numbers of macrophages. In the presence of mercaptoethanol, the plaque-forming capacity of the nonadherent spleen cells was not increased when small numbers of macrophages were added to the system, nor was it decreased when the few macrophages present in the nonadherent cells were further reduced or eliminated. Excess macrophages inhibited antibody formation in the cultures containing mercaptoethanol as they did in control cultures. Optimal restoration of plaque-forming capacity to the nonadherent spleen cells with mercaptoethanol required the reducing agent to be present throughout the 4 or 5 day culture period. Addition of mercaptoethanol 1 or more days after initiation of culture, or transfer of the cells to a medium free of mercaptoethanol before completion of the culture resulted in a reduction in the numbers of plaque-forming cells. The results suggest that mouse lymphoid cells do not require macrophages in order to form antibodies to sheep red cells in vitro, provided mercaptoethanol is present in the culture medium. The mechanism of action of mercaptoethanol under these conditions is not completely clear, but one of its effects is to promote the viability of lymphoid cells in the cultures.

Regulation of the immune system by synthetic polynucleotides. II. Action on peritoneal exudate cells

Incubation of antigen with normal mouse peritoneal exudate cells in vitro and subsequent reinjection of the washed cells into syngeneic mice resulted in increased antibody titers as compared to mice injected with antigen alone. Several of the variables influencing this system were studied with and without the stimulus of complex homoribopolynucleotides (poly A:U or poly I:C) as adjuvants to determine the cellular site of action of the latter. It was found that addition of poly A:U or poly I:C caused a further rise in circulating antibody levels which correlated with increased RNA synthesis, suggesting that the macrophage was one cell affected by this adjuvant. Actinomycin D was found to inhibit the rise in titer induced by PEC and this inhibition could be overcome by poly A:U. Injection of the polynucleotides 18 hr before antigen resulted in depression of circulating antibody levels, and poly A:U or poly I:C injected 18 hr before harvesting PEC and incubation with antigen also inhibited the capacity of the PEC to increase antibody levels. A 4S RNA-rich fraction was purified after treatment with phenol of PEC exposed to antigen in vitro, and under the stimulus of poly A:U this RNA was capable of inducing specific antibody titers and rosette-forming cells on injection into mice. Antigen contamination of Pronase-treated RNA, active biologically, was below 10(-11) g as determined isotopically.

The effects of RES 'blockade' on antibody formation. IV. Inhibition of plaque-forming cells in spleen cultures treated with carbon particles

The effects of colloidal carbon particles on induction of antibody-forming cells in tissue-culture suspensions of spleen cells from normal or sheep erythrocyte primed donor mice were determined. Addition of carbon to normal spleen-cell cultures prevented induction of the `primary' type immune response in vitro. The time at which the carbon was added to the cultures was important, since less suppression occurred when carbon treatment was delayed 48 hours after initiation of culture. Furthermore, the most suppression occurred with the largest dose of carbon used.

Injection of normal donor mice with carbon at various time intervals prior to death interfered with the ability of the spleen-cell suspensions to respond to sheep erythrocytes in vitro by formation of antibody plaques. Maximum suppression occurred when the donor mice were treated with carbon 1–2 days before they were killed.

The anamnestic antibody plaque response in vitro was also suppressed by addition of carbon particles to spleen-cell cultures derived from mice primed with sheep erythrocytes several weeks before they were killed. There was a greater suppression of the 7S than 19S PFC response in vitro. However, the only marked suppression occurred when the highest dose of carbon was used and when it was added to the cultures at `0' time.

Direct injection of carbon into mice primed with sheep erythrocytes 3–4 weeks previously also interfered with the secondary response of the spleen-cell cultures in vitro. Both 19S and 7S antibody-forming cells were suppressed, with a greater suppression of 7S PFCs.

The results of these experiments were interpreted as indicating that phagocytic cells, capable of being `blockaded' in vitro or in vivo by carbon suspensions, are necessary for induction of both primary and secondary type antibody plaque responses in vitro. It seems likely that the carbon particles compete with the red blood cell antigens for a limited number of antigen-processing cells.

Mediation of immunity to tumor isografts in mice by heterologous ribonucleic acid

The growth of tumor isografts in inbred mice is inhibited by intra-peritoneal injections of syngeneic spleen incubated, in vitro, with ribonucleic acid extracted from guinea pigs immunized with the same mouse tumor. This inhibition is partially tumor-specific. Treatment with ribonuclease abolishes the response.

Nucleases in immunity. I. The effect of immunization on RNase and DNase activity in lymphoid tissues

The level of RNase and DNase in the spleen, lymph nodes and thymus glands of mice immunized with sheep erythrocytes was determined. Within 12 hr after immunization there was a moderate decrease in the level of specific RNase activity in the spleen. The depression persisted for several days and then returned to normal. The level of DNase activity also decreased in the spleen of immunized animals, returning to near normal levels on day 4 to 5 and increasing moderately by day 6 and 8.

RNase activity in the lymph nodes and thymus increased rapidly after immunization, reaching a peak level several fold higher than in control animals on days 2 and 6. The level of DNase activity in lymph nodes and thymus was also elevated during the first few days after immunization, but to a lesser extent. The changes in total enzyme activity generally preceded the appearance of haemolytic plaque forming cells. Most of the antibody forming cells were present in the spleen, with peak numbers at day 4. Much fewer antibody forming cells were present in the lymph nodes, and even fewer in the thymus. The relationship between immunogenesis and nucleic acid metabolism in lymphoid tissue was discussed.

Nucleases in immunity. II. Ineffectiveness of exogenous RNase on the antibody plaque response of immunized mice

The effect of bovine ribonuclease on the immune response of mice to sheep erythrocytes was studied. Mice were injected either with a polyribonuclease (poly-RNase) complex once before immunization, or with multiple daily injections of soluble RNase before and after immunization. The number of individual haemolysin-forming cells in the spleens of the animals was determined, as were the serum antibody titres to the erythrocytes. There was no evidence of an immunosuppressive effect in any of the treated animals, as compared to normal, non-treated controls, under conditions in which a marked immunosuppression had been noted in other studies.

Cells involved in the immune response. 13. The nature of the cellular interactions relating antibody formation and immunologic tolerance: a unified hypothesis

The various cells and cell pathways involved in the induction of the primary humoral immune response have been discussed from the point of view of the unitary, as opposed to the multiple, pathway concept. The immunocompetent cells made unresponsive in the immunologically tolerant animal and the cells capable of responding with antibody formation were considered. It is concluded that there exist multiple cellular pathways through which the humoral immune response may be expressed.

The chemical nature of macrophage RNA-antigen complexes and their relevance to immune induction

10 different compounds, including natural and synthetic polypeptides, proteins, polysaccharides, amino acids, and steroid hormones, were assayed for their capacity to form complexes with peritoneal exudate cell RNA. Only molecules carrying negatively charged groups were able to do so. The formation of RNA-antigen complexes was unrelated to the immuno-potency of the "antigen," was not an enzyme-dependent reaction, did not require the synthesis of RNA following introduction of the antigen, did not seem to involve antigen-specific RNAs, was not specific for macrophages, since HeLa cells could be used as effectively, and occurred when purified RNA was mixed with antigen only in the presence of divalent cations. The complexes were very stable, once formed, but could be dissociated by exhaustive dialysis against buffers containing a chelating agent. The macrophage RNA-antigen complex therefore appears to be a chelate between anionic groups on the two components. Based on the total absence of a relationship between immunogenicity and the capacity to form such complexes, as well as the nonspecific nature of complex formation at every level examined, it appears unlikely that RNA-antigen complexes play a physiologically significant role in immune induction.

Macrophage ribonucleoprotein: nature of the antigenic fragment

The antigenic fragments of bacteriophage T2 recovered in RNA derived from macrophages infected with T2 bacteriophage retain their capacity to combine with specific neutralizing antibody to T2. The preservation of the complete native tertiary structure of tail fiber antigen of bacteriophage T2 is not requiired for immucnogenicity.

The immunogenicity of phagocytosed T4 bacteriophage: cell replacement studies with splenectomized and irradiated mice

The role of phagocytosed antigen in the production of antibody to bacteriophage T4 has been studied. The ability of mice to give an antibody response to this antigen was first impaired either by splenectomy or by X-irradiation, and then restored by injection of syngeneic lymphoid cells given at various times relative to the injection of T4. In splenectomized animals administration of lymphoid cells had only a marginal effect on the severely depressed response to T4. It was concluded that the presence of an intact spleen is essential to the development of the normal immune response, and that circulating immunocompetent cells are unable to respond to circulating antigen or to antigen sequestered within the liver. On the other hand, in irradiated mice, there was a faster and more complete restoration of the anti-T4 response, confirming the ability of antigen localized within the spleen to stimulate competent cells. It was also found that the immunogenicity of T4 within this organ was not lost at a rate which corresponded to its gross breakdown but persisted without decrease for at least 48 hr. A similar observation was made for sheep red blood cells when this antigen was used in conjunction with T4.

The actvity of mouse Kupffer cells following intravenous injection of T4 bacteriophage

The response of macrophages from the livers and spleens of mice given a single immunizing dose of T4 bacteriophage has been studied. Following their rapid removal from the circulation, phage particles were found to be concentrated in the liver to a level twelve times that for the spleen. Investigation of the fate of ingested phage showed that it was disposed of more rapidly in the liver than in the spleen, as measured by the disappearance of viable T4 particles and by the loss of radioactive label following injection of [¹³¹I]T4. It was also found that antigen-containing Kupffer cells could elicit little or no antibody synthesis on transfer into normal syngeneic recipients, or on incubation with lymphoid cells in vitro. It is suggested that these macrophages differ from other components of the reticulo-endothelial system in their treatment of T4 antigen, and may be concerned mainly with its breakdown and disposal rather than with providing a stimulus for the initiation of antibody synthesis.

Cells involved in the immune response. VII. The demonstration, using allotypic markers, of antibody formation by irradiation-resistant cells of irradiated rabbits injected with normal allogeneic bone marrow cells and sheep erythrocytes

Bone marrow cells obtained from rabbits of one allotype were injected into irradiated rabbits of a different allotype. The recipients were also injected with sheep red blood cells, and their spleen cells were tested for plaque-forming capacity 7 days later. Spleen cells of all recipients gave large numbers of plaques as did spleen cells incubated with antiserum, directed toward donor allotype. However, incubation of the recipient spleen cells with antiserum directed toward recipient allotype completely suppressed plaque formation. These results demonstrate that antibody-formation in irradiated recipients of transferred lymphoid cells is a property of the recipient animal and that the antibody-forming cell is relatively irradiation-resistant. It was also demonstrated that only viable normal bone marrow cells are capable of transferring antibody-forming capacity to irradiated recipient rabbits. Neither sonicates nor heat-killed preparations of normal rabbit bone marrow cells possessed this capacity.

Cell interactions in the primary immune response in vitro: a requirement for specific cell clusters

Mouse spleen cells were found to associate in cell clusters during the primary immune response to sheep erythrocytes in vitro. About 10% of the cell clusters had the following unique properties; (a) they contained most, if not all, antibody-forming cells, (b) they contained only cells forming antibody to one antigen when cell cultures were immunized with two antigens, (c) the cells in clusters reaggregated specifically after dispersion, and (d) the specific reaggregation of clusters appeared to be blocked by antibody to the antigen. The integrity of cell clusters was required for the proliferation of antibody-forming cells, and prevention of clustering by mechanical means or by excess antibody blocked the immune response. Antibody and antigenic determinants on the surfaces of cells probably provide the basis for interaction. The unique microenvironment of cell clusters was essential for the primary immune response in vitro.