Cellular differentiation of the immune system of mice. I. Separate splenic antigen-sensitive units for different types of anti-sheep antibody-forming cells

The kinetics and morphology of the rosette-forming cell response in the popliteal lymph nodes of rats

A modified ICA technique was used to study the kinetics and morphology of the RFC response in rat popliteal lymph nodes after an inoculation of SRBC into the hind footpad. The primary response was followed over a 10-day period. RFC were classified as either macrophages, haemocytoblasts, plasmacytes or lymphocytes.

RFC present in the popliteal lymph nodes of uninoculated rats were identified as macrophages and lymphocytes. After inoculation the number of RFC rose rapidly to reach a peak at 5–6 days. It was shown that after incubation at 37° certain RFC from inoculated rats had several layers of adherent SRBC and it was suggested that this was an indication of an active secretion of haemagglutinin. 3–4 days after innoculation large mature haemocytoblasts were actively secreting haemagglutinin whilst from the 5th to the 10th day plasmacytes were the RFC involved in the haemagglutinin production. It is suggested that the large haemagglutinin producing haemocytoblasts arise without mitosis via a process of cell transformation and that RF plasmacytes arise via lymphocyte activation into small haemocytoblasts, mitotic division and eventual maturation into immature plasmacytes. RF lymphocytes were thought not to be involved to any extent in haemagglutinin production.

Cellular basis of the genetic control of immune responses to synthetic polypeptides. II. Frequency of immunocompetent precursors specific for two distinct regions within (Phe, G)-Pro--L, a synthetic polypeptide derived from multichain polyproline, in inbred mouse strains

DBA/1 mice are high responders to the (Phe, G) determinant of the synthetic polypeptide (Phe, G)-Pro--L, whereas SJL mice respond well to the Pro--L region of this macromolecule (6). In order to determine whether the phenomenon described above is related to the number of antigen-sensitive units detected for both specificities, and whether responses to these determinants can be transferred independently, graded and limiting inocula of spleen cells from SJL, DBA/1, and F(1) donors were injected into X-irradiated, syngeneic, recipient mice with (Phe, G)-Pro--L. By this approach, one antigen-sensitive unit specific for (Phe, G) was detected in 1.7 x 10(6) and 8.5 x 10(6) spleen cells from immunized and nonimmunized DBA/1 donors, respectively. In contrast, one (Phe, G) relevant precursor was detected in 20 x 10(6) SJL spleen cells, irrespective of whether the donors had been immunized. On the other hand, for the Pro--L specificity, one limiting splenic precursor was found in 1.3 x 10(6) and in 3.4 x 10(6) cells for immunized and nonimmunized SJL donors, respectively; whereas one response unit was estimated for this determinant in 9.4 x 10(6) and in 38 x 10(6) spleen cells from immunized and nonimmunized DBA/1 mice. The findings reported here indicate that the phenotypic expression of the genetic control(s) for immune responsiveness to different immunopotent regions of (Phe, G)-Pro--L is directly correlated with the number of immunocompetent response units detected in two inbred mouse strains. In the spleens of immunized F(1) donors, similar frequencies of one limiting precursor in 3.0 x 10(6) and in 2.8 x 10(6) cells were detected for (Phe, G) and Pro--L, respectively. The results of a chi-square test for independence of (Phe, G) and Pro--L responses in F(1) animals is compatible with the hypothesis that the transferred spleen cells limiting the response to (Phe, G)-Pro--L are restricted to generate antibodies specific for only one of the two determinants of this macromolecule.

Surface antigens of immunocompetent cells. I. Effect of theta and PC.1 alloantisera on the ability of spleen cells to transfer immune responses

Spleen cell transfer studies were done in BALB/c strain mice in an attempt to define the role of theta-antigen-bearing lymphoid cells in immune responses to SE. Incubation with alloantiserum to theta-C3H and rabbit C' virtually completely abolished the ability of the cells to transfer both primary and secondary (IgM and IgG) responses to 650 R irradiated recipients. Normal thymus cells partially reconstituted the ability of such treated cells to transfer the primary but not the secondary response. The results are interpreted as showing immunological memory for SE in the theta-bearing thymus-derived cells. Incubation of the spleen cells with alloantiserum to the PC.1 antigen present on antibody-forming cells did not significantly affect the ability to transfer either primary or secondary response.

Antigen-specific cells in mouse bone marrow. I. Lasting effects of priming on immunocyte production by transferred marrow

Graded numbers of marrow cells and 5 x 10(7) thymocytes were mixed in vitro and transplanted into X-irradiated (C3H x C57BL/10)F(1) mice. Upon injection of sheep or chicken erythrocytes, splenic plaque-forming cells secreting IgM (direct PFC) or IgG (indirect PFC) hemolytic antibody were enumerated at the time of peak responses. Anti-sheep and anti-chicken primary PFC responses elicited by nonimmune marrow cells differed sharply from each other under the conditions of limiting dilution assays. The frequencies of anti-chicken responses in recipients of different numbers of marrow cells conformed to the predictions of the Poisson model, while the frequencies of anti-sheep responses did not. Hence, the function of certain marrow-derived cells was expressed differentially during the two immune responses, to exclude that the same precursor units generated anti-sheep or anti-chicken PFC. The former precursor cells or units were functionally more heterogeneous than the latter. Immunization of marrow donors against sheep erythrocytes did not alter the population of cells engaged in anti-chicken responses, since limiting dilution assays with immune and nonimmune marrow cells gave identical results. However, anti-sheep immunization altered specifically the cell population engaged in anti-sheep responses, in two ways: (a) potentially immunocompetent marrow cells underwent antigen-dependent differentiation or maturation, to become functionally homogeneous. Consequently, the frequencies of PFC responses in limiting dilution assays conformed to the Poisson model; the changes occurred independently in class-restricted precursors of direct and indirect PFC. (b) marrow cells capable of inhibiting precursors of direct anti-sheep PFC arose in primed mice. The inhibition, which was specific, could have been effected directly by marrow cells or by a diffusable product such as IgG antibody. Results indicated that potentially immunocompetent cells of mouse marrow with distinct functions were antigen specific and antigen sensitive.

Cellular aspects of the inverse relationship between the net charge of immunogens of antibodies elicited

The results reported establish a cellular basis for the inverse relationship between the net electrical charge of immunogens and of the antibodies provoked by them. Glass bead columns were used to reduce the number of immunocompetent spleen cells preferentially reactive with more acidic immunogens. After a single immunization, titers of antibodies to an acidic dinitrophenylated copolymer of tyrosine, glutamic acid, and lysine (DNP-901) elicited in recipient mice by filtered spleen cells were significantly lower than those generated by unfiltered cells. After secondary stimulation, the major portion of the antibodies provoked by the acidic antigen was found in the more acidic fraction eluted from DEAE-Sephadex, in contrast to the more basic antibodies, of the same specificity, generated by unfiltered spleen cells. Results obtained by transplanting a limiting number of spleen cells indicate a depletion in the number of precursor cells reactive with dinitrophenyl on DNP-901 after glass bead chromatography, whereas there was no change in the response to dinitrophenyl on a basic copolymer, DNP-912, containing the same amino acids in different molar ratios.

Cellular basis of the genetic control of immune responses to synthetic polypeptides. I. Differences in frequency of splenic precursor cells specific for a synthetic polypeptide derived from multichain polyproline ((T,G)-Pro--L) in high and low responder inbred mouse strains

SJL mice are high responders to the synthetic multichain polypeptide antigen (T,G)-Pro--L, whereas DBA/1 mice are low responders (10, 11). In order to determine whether the genetic control of immune response can be correlated with the number of antigen-sensitive precursor cells, spleen cell suspensions from normal and immunized SJL and DBA/1 donor mice were transplanted into lethally X-irradiated syngeneic recipients (incapable of immune response) along with (T, G)-Pro--L. Anti-(T, G)-Pro--L responses (donor-derived) were assayed in the sera of the hosts 12-16 days later. By transplanting graded and limiting numbers of spleen cells, inocula were found which contained one or a few antigen-sensitive precursors reactive with the immunogen. Using this method to estimate the relative numbers of such cells for the high responder SJL strain, one precursor was detected in approximately 1.3 x 10(6) and approximately 7.2 x 10(6) spleen cells from immunized and normal donors, respectively. In contrast, one precursor was detected in about 30 x 10(6) spleen cells from low responder DBA/1 mice, irrespective of whether the donors had been immunized. These results indicate that the genetic control of immunity to the synthetic polypeptide antigen investigated is directly correlated to the relative number of precursor cells reactive with the immunogen in high and low responder strains.

Cellular differentiation of the immune system of mice. VI. Strain differences in class differentiation and other properties of marrow cells

Marrow cells and 5 x 10(7) thymocytes of unprimed (C57BL/6 x DBA/2)F(1), (C57BL/10 x WB)F(1) and (C3H x C57BL)F(1) donor mice were mixed in vitro and transplanted into X-irradiated syngeneic hosts. Upon injection of sheep erythrocytes, splenic plaque-forming cells (PFC) secreting IgM (direct PFC or IgG (indirect PFC) hemolytic antibody were enumerated at the time of peak responses. By grading the numbers of marrow cells, inocula were found that contained few immunocompetent cells reaching the recipient spleens, interacting with thymocytes or other accessory cells (or both), and generating PFC. The frequency of responses in BDF(1) mice conformed to Poisson statistics, indicating that immunocompetent marrow cells participated in a single-hit interaction limiting PFC responses. The marrow cells assayed were not restricted for the antibody class (IgM versus IgG) to be secreted by mature PFC. Unrestricted marrow cells could have been either the precursors of PFC or accessory cells. Different results were obtained in BWF(1) and C3BF(1) mice. The frequency of responses in relation to the number of marrow cells grafted did not follow Poisson statistics, and the limiting cells were restricted for antibody class. Presumably, immunocompetent cells of these strains were more heterogeneous than those of BDF(1) mice and participated in a multiplicity of cell-to-cell interactions. The strain differences reflected inherent properties of marrow cells and not influences of the environment in which PFC were produced. The results confirmed for bone marrow the heterogeneity of immunocompetent cells reported by others for spleen, and suggested that genetic factors such as "immune response" genes regulate cellular differentiation also for functions other than those related to antibody specificity.

Immunological alteration of leukemic cells in vivo after treatment with an antitumor drug

L1210 leukemia was transplanted serially in CDF(1) mice treated with 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DIC, NSC 45388). After four different lines (C lines) had been treated for several generations, a marked increase in survival time of untreated mice was observed. In contrast, mice treated with DIC or immunosuppressed with cyclophosphamide succumbed earlier with generalized leukemia. Furthermore, a C line showed unusually high sensitivity to chemotherapeutic treatment with 1,3 bis(2-chloroethyl)-1-nitrosourea. The data suggest that C lines acquired strong antigenicity for CDF(1) and DBA/2 hosts. DIC treatment may have selected highly antigenic variants or induced somatic mutations resulting in the appearance of strong new transplantation antigen(s).

Electrophoretically homogeneous antibody synthesized by spleen foci of irradiated repopulated mice

10(6) splenocytes from primed donors were injected, together with sheep erythrocytes (SRBC), into X-irradiated syngeneic mice. 8 days later the spleens were excised and cut into small fragments, keeping track of their location in the organ. Each fragment was cultured individually for 24 hr in the presence of (14)C amino acids and the culture fluids were assayed for antibody activity. The antibody-producing fragments were found to be clustered in few restricted areas (foci) surrounded by negative tissue. The anti-SRBC antibody from single foci was purified by absorption on stroma followed by acid elution. Thereafter, it was subjected to electrophoresis and immunoelectrophoresis. The radioautography of the runs showed a considerable degree of homogeneity. Distinct and sharp spikes were localized in the beta and gamma region. The pattern of each focus is unique from the point of view of the number of spikes and their mobility. Eluates obtained from many pooled fragments gave a broad radioactive smear in beta-gamma region. Many foci synthesized antibody migrating as a single band. This homogeneous protein is probably the product of a clone of cells homogeneously differentiated. However, some foci producing two and probably more antibody bands were also encountered. Two interpretations of the finding can be given. Either more than one precursor may participate in the formation of a focus or a differentiation switch may occur during the clonal expansion.

Replica analysis of the class of antibodies produced by single cells

Improvements have been made in a localized haemolysis in gel replica assay developed previously. The technique is designed to show if an individual antibody producing cell releases antibody of one or more classes. The techniques can also be used to indicate the specificity of antibodies produced by individual cells by using two different antigens in the test system. In experiments where both slides of a slide-pair are untreated or treated identically, and 100% coincidence of plaques is expected, the technique has been shown to detect about 95% coincidence. Pairs of slides treated differently to reveal plaques due to antibodies of different classes show a mean of about 3·5% coincident plaques. This `background' of coincidence which it is thought is not due to `double-producers', is one of the limiting factors of the technique.

Distinct events in the immune response elicited by transferred marrow and thymus cells. I. Antigen requirements and priferation of thymic antigen-reactive cells

Marrow cells and thymocytes of unprimed donor mice were transplanted separately into X-irradiated syngeneic hosts, with or without sheep erythrocytes (SRBC). Antigen-dependent changes in number or function of potentially immunocompetent cells were assessed by retransplantation of thymus-derived cells with fresh bone marrow cells and SRBC; of marrow-derived cells with fresh thymocytes and SRBC; and of thymus-derived with marrow-derived cells and SRBC. Plaque-forming cells (PFC) of the direct (IgM) and indirect (IgG) classes were enumerated in spleens of secondary host mice at the time of peak responses. By using this two-step design, it was shown (a) that thymus, but not bone marrow, contained antigen-reactive cells (ARC) capable of initiating the immune response to SRBC (first step), and (b) that the same antigen complex that activated thymic ARC was required for the subsequent interaction between thymus-derived and marrow cells and/or for PFC production (second step). Thymic ARC separated from marrow cells but exposed to SRBC proliferated and generated specific inducer cells. These were the cells that interacted with marrow precursors of PFC to form the elementary units for plaque responses to SRBC, i.e. the class- and specificity-restricted antigen-sensitive units. It was estimated that each ARC generated 80-800 inducer cells in 4 days by way of a minimum of 6-10 cell divisions. On the basis of the available evidence, a simple model was outlined for cellular events in the immune response to SRBC.

Cellular differentiation of the immune system of mice. V. Class differentiation in marrow precursors of plaque-forming cells

Marrow cells and thymocytes of unprimed donor mice were mixed in vitro and transplanted into X-irradiated syngeneic hosts. 18 hr later sheep erythrocytes were injected to induce immune responses. Splenic plaque-forming cells (PFC) secreting IgM (direct PFC) or IgG (indirect PFC) hemolytic antibody were enumerated at the time of peak responses. By transplanting graded and limiting numbers of marrow cells with 5 x 10(7) thymocytes, inocula were found that contained few precursors of PFC (P-PFC) reaching the recipient spleens, interacting with thymocytes, and generating PFC. However, the frequency of responses in relation to the number of grafted marrow cells did not follow Poisson statistics, presumably because the interaction of marrow cells with thymocytes was more complex than a single or a one-to-one cell event. The frequency of direct PFC responses was greater than that of indirect PFC responses in 13 of 15 groups of mice tested. This was interpreted as evidence for the existence of two classes of P-PFC, each of which was restricted to generate either direct or indirect PFC. The precursors of direct PFC were approximately 15 times more frequent than those of indirect PFC. Since thymic antigen-reactive cells were not differentiated for antibody class, it follows that antigen-sensitive units reactive to sheep erythrocytes owe their class restriction to specialized marrow cells. Specialization of P-PFC may have arisen within marrow cell lines by differentiation, or may have been conferred upon P-PFC by interaction with other cells, including those of the irradiated host.

Cellular differentiation of the immune system of mice. IV. Lack of class differentiation in thymic antigen-reactive cells

Thymocytes and marrow cells of unprimed donor mice were mixed in vitro and transplanted into X-irradiated syngeneic mice. 18 hr later, sheep erythrocytes were injected to induce immune responses. Splenic plaque-forming cells (PFC) secreting IgM (direct PFC) or IgG (indirect PFC) hemolytic antibody were enumerated at the time of peak responses. By transplanting graded and limiting numbers of thymocytes with 4 x 10(7) marrow cells, inocula were found which contained one or a few thymic antigen-reactive cells (ARC) reaching the recipient spleens, interacting with marrow cells, and inducing PFC formation. The frequency values of ARC inferred from direct and indirect plaque assays were very similar, 1 in approximately 10(7) thymocytes. Furthermore, statistical analysis indicated that the formation of direct PFC was not independent of the formation of indirect PFC. This was interpreted to mean that ARC were not specialized themselves and did not determine the molecular class of antibody to be secreted after interaction with marrow cells. Spleens of thymus-marrow grafted mice containing one or two ARC and non-limiting numbers of marrow precursors of PFC (P-PFC), had direct and indirect PFC clustered in several focal areas. Assuming that each focal area represented the progeny of one P-PFC that had interacted with ARC, these results confirmed the statistical evidence for lack of class differentiation in thymic ARC, and also indicated that each ARC or its progeny cells interacted with more than one P-PFC of either class.

Maturation of hemolysin-producing cell clones. I. The kinetics of the induction period of an in vitro hemolysin response to erythrocyte antigen

INVESTIGATIONS OF THE INDUCTION PERIOD OF AN IN VITRO HEMOLYSIN RESPONSE TO SHEEP ERYTHROCYTE ANTIGEN REVEALED THE FOLLOWING: 1. After antigen stimulation precursors of plaque-forming cells rapidly maturate to the point of hemolysin production. 2. Initial maturation probably occurs in the absence of cell division. 3. After initial maturation, a latent period of about 12 hr occurs before the first doubling of PFC. 4. At least the first three cell doublings are synchronous, with a generation time of 7-8 hr. 5. Synchronous cell division implies that all precursor cells are at the same point in the cell cyde when they are initially stimulated.

Cellular differentiation of the immune system of mice. 3. Separate antigen-sensitive units for different types of anti-sheep immunocytes formed by marrow-thymus cell mixtures

Marrow cell suspensions of unprimed donor mice have been transplanted into X-irradiated syngeneic hosts. 5-46 days later, bone cavities and spleens contained regenerated cells of the immune system which required interaction with thymocytes (from intact donors) and antigen (SRBC) to form antigen-sensitive units (ASU) and to generate mature immunocytes. These cells were capable of differentiating either into direct or indirect hemolytic plaque-forming cells (PFC). The precursors of PFC regenerated earlier than the other cell type necessary for immunocompetence, the antigen-reactive cell (ARC). The latter was not found until 10 or more days after transplantation. Availability of ARC was inferred from PFC responses elicited by grafted mice challenged with SRBC at varying intervals. In a second series of experiments, graded numbers of marrow cells (ranging from 10(7) to 5 x 10(7)) were transplanted with 5 x 10(7) or 10(8) thymocytes into irradiated mice, and SRBC were given 18 hr later. After 9-12 days the recipient spleens contained all or some of the following immunocytes: direct and indirect PFC, and hemagglutinating cluster-forming cells. The frequency of each immune response varied independently of the others, but in relation to the number of marrow cells grafted. This was interpreted to indicate that ASU formed in irradiated mice by interaction of marrow and thymus cells were similar to those of intact mice. In particular, they were specialized for the molecular class (IgM or IgG) and function (lysis or agglutination) of the antibody to be secreted by their descendent immunocytes. Hence, class-differentiation appeared to be conferred upon ASU by their marrow-derived components.

Requirement for continuous antigenic stimulation in the development and differentiation of antibody-forming cells. The effect of passive antibody on the primary and secondary response

The essential role of continuous antigenic stimulation in the development and differentiation of antibody-forming cells as defined in the X-Y-Z immune cell maturation scheme was examined in these studies. Mice were primed with sheep erythrocytes (SRBC) in an attempt to induce maximum immune progenitor cell conversion (X --> Y). Subsequently antigen was depleted at 1 or 4 days after priming with isologous specific antibody in order to interrupt further immune cell differentiation (Y --> Z). It was reasoned that this condition would result in depression of the functional antibody-producing cell compartment as measured in the intact mice and subsequently in enhancement of the sensitized (Y cell) compartment as measured in the spleen cell transfer system. These data were also correlated with systematic studies of the hyperplasia of the spleen germinal centers. The effect of passive antibody on the primary response to SRBC was a marked decrease indirect and indirect hemolysin-producing cells (DPFC and IPFC). However, there was a lack of correlation in the degree of antibody-mediated 19S and 7S immune cell suppression during the primary response, the DPFC being much less depressed than the IPFC. As measured in the transfer system there was an enhanced 19S sensitized cell compartment and a depressed 7S sensitized cell compartment in 1 day passively immunized mice. This was true whether or not transfers were performed 1, 2, or 4 wk after priming. Similarly, there was an enhanced 19S-sensitized cell compartment with little or no effect on the 7S-sensitized. cell compartment in 4 day passively immunized mice. These data suggest that progeny of the antigen-stimulated progenitor cells (X cell), as a consequence of lack of further antigenic stimulation, were forced into maturation arrest. These studies further demonstrate that isologous passive antibody suppresses germinal center growth regardless of whether the antibody is infused 1, 2, or 4 days after priming. In terms of formation of sensitized cells, the marked depression of 7S sensitized cell compartment after passive immunization at 24 hr in contrast to the enhancement of the 19S sensitized cell compartment corresponds to the suppressed growth of germinal centers during the primary response. Thus, if the germinal center is, as suggested, the site of proliferative expansion of immunocompetent cells, these data indicate that the germinal center growth is related to the 7S antibody response and in the formation of "7S memory."

Cells involved in the immune response. VI. The immune response to red blood cells in irradiated rabbits after administration of normal, primed, or immune allogeneic rabbit bone marrow cells

Irradiated rabbits given allogeneic bone marrow cells from normal adult donors responded to an injection of sheep red blood cells by forming circulating antibodies. Their spleen cells were also capable of forming many plaques using the hemolysis in gel technique, and were also capable of undergoing blastogenesis and mitosis and of incorporating tritiated thymidine upon exposure to the specific antigen in vitro. However, irradiated rabbits injected with allogeneic bone marrow obtained from rabbits injected with sheep red blood cells 24 hr prior to sacrifice (primed donors) were incapable of mounting an immune response after stimulation with sheep red cells. This loss of reactivity by the bone marrow from primed donors is specific for the antigen injected, since the immune response of the irradiated recipients to a non-cross-reacting antigen, the horse red blood cell, is unimpaired. Treatment of the bone marrow donors with high-titered specific antiserum to sheep red cells for 24 hr prior to sacrifice did not result in any diminished ability of their bone marrow cells to transfer antibody-forming capacity to sheep red blood cells. The significance of these results, with respect to the origin of the antigen-reactive and antibody-forming cells in the rabbit, is discussed.

Cellular differentiation of the immune system of mice. II. Frequency of unipotent splenic antigen-sensitive units after immunization with sheep erythrocytes

Spleen cell suspensions of primed donor mice containing precursors of immunocytes have been transplanted into X-irradiated recipient mice 122-138 days after immunization. Following secondary stimulation with antigen (sheep erythrocytes), these precursors, called antigen-sensitive units (ASU), gave rise to progeny cells secreting specific antibody in the spleens of recipients. Single cells releasing IgM hemolysins (direct plaque-forming cells or PFC), IgG hemolysins (indirect PFC), and hemagglutinins (cluster-forming cells or CFC) were enumerated. By transplanting graded and limiting numbers of primed spleen cells, inocula were found which contained one or a few ASU reaching the recipient spleens. We estimated, thereby, the frequency of ASU detectable by our procedures in donor cell suspensions. The values obtained from direct and in-indirect plaque assays, and from cluster assays were 1 in approximately 8.0 x 10(5), 1 in approximately 4.4 x 10(5), and 1 in approximately 5.9 x 10(5) nucleated spleen cells, respectively. The number of splenic ASU for direct PFC was not greater than that of unimmunized mice; however, immunization greatly increased the number of splenic ASU for indirect PFC and for CFC. By applying to each recipient spleen direct and indirect plaque tests and cluster tests, we found that positivity for each type of immunocyte was independent from that of the other two types. These results confirm the unipotent nature of splenic ASU in general, and document the commitment of ASU primed with SRBC to generate progeny cells secreting antibody of a single molecular (IgM or IgG) or functional (lysin or agglutinin) class. We concluded that splenic ASU are composed of relatively differentiated cells of the immune system of mice. With respect to specificity and class differentiation, ASU appear to be as specialized as antibody-producing cells themselves. Our results did not support the view that ASU-derived clonal populations shift from IgM to IgG antibody production.