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

Virulence and attenuation of murine cytomegalovirus

Murine cytomegalovirus (MCMV) was rapidly and regularly attenuated by passage through mouse embryo cell culture. This attenuation was manifested by alteration of lethality for suckling mice and by a striking loss of capacity to multiply in liver and spleen of weanling mice. The attenuation was selective in that the passaged virus multiplied vigorously in other organs and established high titer infections in submaxillary glands and pancreas comparable to those seen with wild virus. Furthermore, attenuated virus no longer induced transient suppression of antibody and interferon responsiveness which was a regular feature of wild MCMV infection. Wild and attenuated MCMV shared the property of being poor immunogens. They induced anti-CMV complement-fixing or neutralizing antibody very slowly with barely detectable levels present at the end of the first 2 weeks of infection. The close antigenic relationship between wild and attenuated agents was demonstrated by nearly identical neutralization by a rabbit antiserum induced with wild MCMV. Furthermore, survivors of neonatal infection with attenuated virus were fully protected against subsequent challenge with potentially lethal doses of wild MCMV. Virulence could be rapidly restored by back passage in mice.

Lymphocyte cell subpopulations during acute post-streptococcal glomerulonephritis: cell surface antigens and binding of streptococcal membrane antigens and C-reactive protein

T lymphocyte surface markers were examined in 23 patients with acute post-streptococcal glomerulonephritis (AGN) in parallel with normal controls and individuals without nephritis who showed evidence of pharyngeal or skin-sore beta-haemolytic streptococcal infection. Numbers of T gamma cells were similar in AGN and normal controls but were significantly lower (P less than 0.05) than those in skin-sore culture-positive streptococcal infection controls. Numbers of T mu cells were similar in AGN and normal controls but were lower (P less than 0.05) than those observed in streptococcal controls. Percentages of T mu cells were similar in AGN and normal controls but were lower (P less than 0.05) than those recorded in streptococcal infection control groups. Proportions of T cells were reduced during AGN (P less than 0.05). Lymphocytes capable of binding type 12 group A streptococcal membranes were increased (30.4%) in patients with AGN as compared to normal controls (4.1%). Subjects with streptococcal infection alone showed elevated but intermediate relative numbers (10.5%) of lymphocytes binding group A membranes. Increased relative numbers of both B and T lymphocytes binding group A streptococcal membranes were present in both AGN and non-nephritogenic streptococcal infection controls.

Purification and chemical characterization of antigens from sheep erythrocytes

A mixture of glycoproteins and glycolipids was solubilized from sheep erythrocytes membranes under the effect of high ionic strength (2 M NaCl, 0.5 M Tris). Several antigenic fractions could be purified from the mixture using gel filtration on Sephadex G-200 and block electrophoresis on Pevikon C870; two fractions were found to raise antibodies in a primary reaction and these antibodies effectively sensitized erythrocytes to lysis by complement. The majority of other fractions elicited a weaker primary reaction which was detectable by both agglutination and haemolysis. The fraction, migrating fastest towards the cathode, elicited after immunization a formation of antibodies that could be detected almost exclusively by haemagglutination. The fraction, which elicited in the primary reaction a high titre of haemolytic antibodies, is composed of 72% proteins, 11% lipids and 15% saccharides.

Effect of age on immune function in terms of chemically induced cancers

Neonatal, fetal, and very old animals are particularly sensitive to chemical carcinogenesis. Reasons for this increased sensitivity could be due to increased susceptibility of "target" organs or cells, peculiar hormonal levels at these age groups, relatively deficient immune functions, or combinations of these and/or other factors. During the late fetal and first three weeks of neonatal life, the immune system is rapidly maturing, is relatively incompetent, and its diverse components are developing at different rates. For example, thymus-dependent (T) alloreactive cells capable of proliferating in mixed lymphocyte reactions (T helper cells) develop by 7 days of age, but precursors of T killer cells are not competent until approximately 14 days of age. Bursa equivalent-dependent (B) cells capable of generating antibody responses are present in fetal liver but are extremely sensitive to tolerance induction until 10-14 days of age when IgD cell surface receptors are detectable. Marrow-dependent (M) cells responsible for regulation of suppressor cells and for natural cytotoxicity to transformed tumor cells do not mature until 3 weeks of age. In very old animals, the thymus is atrophic and cell-mediated immunity is moderately suppressed. Natural cytotoxicity against tumor cells is less than normal but antibody formation (B cell function) is adequate. Gonadotrophic hormones of the pituitary or placenta are high during pregnancy, the early neonatal period, after the menopause, and in a large fraction of men over 60 years of age. These and other hormones are immunosuppressive and could theoretically facilitate carcinogenesis. The particular immune cell type, if any, responsible for resistance to chemically induced tumors has not been determined. One can only state that susceptibility to chemical carcinogenesis is associated with a relative dysfunction of the immune system and that age is an important factor.

Quantification of antigen-reactive cells among human T lymphocytes

The number of antigen-reactive cells among human peripheral blood T lymphocytes was estimated by a limiting dilution analysis. Antigen-induced lymphocyte activation was measured by means of incorporation of tritiated thymidine [3H]dThd. We have studied the frequency of memory T cells for the bacterial antigens tuberculin PPD and tetanus toxoid in immune donors, as well as the frequency of alloantigen-reactive T cells. In 11 different donors, the observed frequencies of the antigen-reactive T cell ranged between 1:300 and 1:16 000 for PPD; for tetanus toxoid values, between 1:750 and 1:11 500 were obtained in 5 different donors. The frequency of alloantigen-reactive T cells was found to be higher: between 1:200 and 1:600 (n = 10). For 3 donors, the estimated frequencies proved to be reproducible over a period of several months. Finally, a correlation could be demonstrated between the frequency of PPD-reactive T cells and the [3H]dThd incorporation of 4 X 10(4) PPD-stimulated lymphocytes.

Cell transfer studies with the DK/or inbred chicken lines

The histoincompatibility in the DK-OR-1 (B13B13) and DK/OR-3 (B19B19) inbred White Leghorn chicken lines was assessed with the Simonsen's spleen assay, GVHR mortality counts and antibody production by transferred cells in embryonic in vivo hosts. The two lines appear to be sufficiently histocompatible for use in cell transfer experiments. The occurrence of antigen responsive cells (ARC) and precursor cells in bone marrow as assessed with the in vivo culture and baby chick immune enhancement assays. Bone marrow of unimmunized donors possessed very little anti-MRBC immune responsiveness. Bone marrow cells from MRBC-primed donors, however, showed low anti-MRBC activity in the in vivo culture which could be elevated with a second antigen stimulation. Chicks grafted as embryos with bone marrow from immunized donors responded to MRBC immunization in an enhanced manner as compared to the control untreated chicks which responded poorly if at all to the antigen. Immunization appears (a) to increase the pool of potential ARC in the bone marrow of the donor and (b) to augment the responsiveness of bone marrow cells transferred into embryonic hosts.

Limiting dilution analysis of helper T-cell function

Limiting dilution analysis has been applied to the study of T-cell 'helper' function in vitro. Using the microculture system one can estimate the numbers of (a) 'helper' T cells involved in specific collaboration with B cells and (b) those T cells which are able, on being activated by their specific antigen, to facilitate the response of B cells to another antigen. Such studies have enabled us to demonstrate that: (1) a single 'helper' T cell was able to activate a single B-cell precursor to detectable antibody production; (2) the 'helper' function of primed T cells was radio-resistant; (3) a minimal estimate of 'helper' frequencies could be obtained in defined cell populations; (4) nonspecific facilitation was directed towards virtually all available B cells of a given specificity if these were challenged with their appropriate particulate antigen; (5) the microculture system offers the opportunity to determine whether specific and non-specific T-cell 'helper' effects are a consequence of the activity of one T-cell type or of differenct subpopulations of T cells.

Cell-mediated immune responses in vitro. I. Suppression of the generation of cytotoxic lymphocytes by concanavalin A and concanavalin A-activated spleen cells

The effects of soluble concanavalin A (Con A) or Con A-activated spleen cells on the generation of cytotoxic lymphocytes (CL) in mixed leukocyte cultures (MLC) were examined. Mitogenic concentrations of soluble Con A or small numbers of Con A-activated spleen cells substantially inhibited CL responses. The suppression was partial rather than absolute and was critically dependent upon the concentration and time of addition of soluble Con A or Con A-activated spleen cells to the MLC. Suppressive effects of Con-A activated spleen cells were mediated by T cells since suppressor cell activity was abrogated by treatment of spleen cells with anti-theta serum and complement before or after Con A activation. X irradiation of spleen cells before Con A treatment also abrogated generation of suppressor cell activity. After activation by Con A, however, the function of suppressor cells was radioresistant. Although the precise mechanism(s) of suppression is, as yet, unknown, the precursors of CL must be exposed to Con A-activated cells during the early phases of the immune response for suppression to occur. Kinetic studies revealed that suppression of CL responses was not due to a failure to initiate an immune response, but represented a response which developed initially, but subsequently aborted. The relevance of these observations to the concepts of T-cell-T-cell interaction and regulatory control of immune responses by T cells is discussed.

Cells binding the antigen keyhole limpet haemocyanin in the peripheral blood and in the lymphocyte cultures of non-immune and immunized human subjects

Cells binding the antigen Keyhole limpet haemocyanin (KLH) were detected among human peripheral blood leucocytes and antigen-stimulated cultured lymphocytes. They were detected by their formation of rosettes with antigen-coated human O red blood cells. In the peripheral blood 0·13% of the lymphocytes of non-immune and 0·80% of the lymphocytes of immune subjects were antigen binding. In KLH-stimulated cultures of the lymphocytes of non-immune subjects there were 0·1% antigen-binding cells and in those of immune subjects there were 8·5% antigen-binding cells. Binding was specific. Thus, lymphocytes from phytohaemagglutinin- and streptolysin O-stimulated cultures did not bind KLH-coated red blood cells and did not form rosettes with KLH-stimulated lymphocytes. Incubation of KLH-stimulated lymphocytes with heterologous anti-immunoglobulin serum revealed that the KLH receptor was related to IgM. Addition of metabolic blocking agents (puromycin, cycloheximide, actinomycin-D and arabinosyl cytosine) to KLH-stimulated lymphocyte cultures revealed that the generation of antigen-binding cells required both DNA and protein synthesis. After primary immunization of normal human subjects, antigen-binding cells were detected in their appropriate lymphocyte cultures at 7 days and reached their maximum level at 21 days, in five of the six kinetically followed individuals and at 14 days in the other. This data represents the first report of the generation of antigen-binding cells in lymphocyte cultures demonstrated by the rosette method. These methods should be useful in the study of a variety of immunological problems in man.

The relationship between the immunoglobulin class of B-cell precursors and the degree of synergism obtained from the presence of T cells

In thymus–bone marrow synergy experiments the γG response is considerably more dependent on T-cell help than is the γM response. No difference in radiation sensitivity between γM and γG precursor cells could be detected. γG1–PFC were found to be more sensitive to a lack of protein in the suspending medium than γG2a or γM–PFC.

Mode of action of a supernatant activity from T-cell cultures that nonspecifically stimulates the humoral immune response

The mode of action of "allogeneic supernatant" (the culture supernatant of a 24-hr mixedlymphocyte reaction), has been studied. This factor stimulates the response of spleen cell cultures depleted in thymus-derived lymphoid cells (T-cells) to antigens that elicit a thymus-dependent response. We used a limiting dilution analysis, in which the frequency and size of response of individual bone-marrow-derived lymphoid cells (B-cells) could be measured. In confirmation of other reports, the occurrence of B-cells responding to antigen under different conditions was shown to follow a Poisson distribution in mouse spleen cell suspensions. Allogeneic supernatant increased responses to thymus-dependent antigens, both by increasing the frequency of B-cells whose response is initiated and by increasing the numbers of antibody-forming cells obtained from each responding B-cell. Two fractions were obtained by dialysis of the supernatant. The nondialyzable fraction contained factors able to increase both the frequency of B-cells responding to sheep erythrocytes, and the size of the responding unit. The dialysate contained factors that were only able to increase the numbers of antibody-forming cells obtained per responding B-cell from B-cells whose response had already been initiated by antigen-specific T-cells. Since the nondialyzable factors were active in the absence of detectable functional T-cells, it was concluded that these factors, produced by T-cells, might represent one mechanism whereby T-cells cooperate with B-cells in the initiation or development of a humoral immune response.

Hemolytic plaque formation by leukocytes in vitro. Control by vasoactive hormones

Histamine, beta-adrenergic amines, and prostaglandins inhibited hemolytic plaque formation by splenic leukocytes from immunized mice. The same agents had previously been shown to prevent both the IgE-mediated release of histamine from human basophils and the immunologically specific cytolytic activity of murine lymphocytes, through stimulation of the production of cyclic AMP in leukocytes. We therefore tested the hypothesis that cyclic AMP might mediate an inhibitory effect of these drugs by comparing the ability of these agents to inhibit plaque formation with their effects on cyclic AMP accumulation in leukocytes. In splenic cells from three mouse strains, the dose-dependent effects of these agents of cyclic AMP correlated with their inhibition of plaque formation. Beta- but not alpha-adrenergic agonists were effective in both systems, and the effects of isoproterenol were inhibited by propranolol. Histamine was approximately equipotent with isoproterenol in both systems. Two prostaglandins (E(1) and E(2)) were effective in both systems, but prostaglandin F(2alpha) was not. Dibutyryl cyclic AMP, a lipid-soluble analog of the endogenous nucleotide, inhibited plaque formation by cells of all three strains. Theophylline, an inhibitor of cyclic AMP degradation, inhibited plaque formation slightly, but potentiated the effects of histamine, isoproterenol, and the prostaglandins on both cyclic AMP accumulation and plaque formation. Finally, cholera enterotoxin, a potent activator of adenyl cyclase, produced a delayed inhibition of plaque formation and a parallel increase in leukocyte cyclic AMP content; both effects of the toxin were blocked by canine antitoxin. These results suggest that leukocyte cyclic AMP may act as a "second messenger" to suppress plaque formation in vitro. The inhibitory effects of hormones and cyclic AMP on plaque formation are strikingly similar to their effects on in vitro models of immediate and cell-mediated hypersensitivity. The physiologic significance of these findings is not yet known.

Separation of specific antibody-forming mouse cells by their adherence to insolubilized endogenous hormones

Spleen cells from mice immunized with sheep red cells were separated by differential adherence to insolubilized histamine, catecholamines, and prostaglandins. The hormones were insolubilized by linking them to Sepharose beads through a protein carrier. We measured hemolytic plaque formation (per million splenic leukocytes) of cells which passed through columns of hormone-carrier-Sepharose beads (i.e., those cells that failed to bind). As compared with control (no column) cells, the number of plaque-forming cells was substantially reduced by passage through histamine, epinephrine, isoproterenol, and prostaglandin-E(2) columns. Plaque-forming cells were not significantly reduced by passage through carrier Sepharose (another control) or norepinephrine- and prostaglandin-F(2alpha)-carrier Sepharose columns. Thus, the ability of an insolubilized hormone preparation to subtract plaque-forming cells roughly correlated with the presence of pharmacologic receptors for the corresponding free hormones, as judged by stimulation of cyclic AMP accumulation in the same cells, reported previously. Both 19S and 7S plaque-forming cells were subtracted by columns prepared from pharmacologically active hormones, but none of the insolubilized hormones stimulated accumulation of intracellular cyclic AMP. The cell membrane phenomenon that allows adherence to a given hormone-carrier-bead column may be identical with the cell receptor.

Graft-versus-host reactions in mice. IV. Thymus cell suppression of antibody formation

The ability of transplanted marrow-thymus cell mixtures to generate antibody-forming cells in irradiated syngeneic or F(1) hybrid mice when immunized with sheep erythrocytes 18 hours later was determined. Much fewer anti-sheep plaque-forming cells (PFC) were detected in spleens of F(1) hybrid mice. Adrenalectomy, use of infant recipient mice, or preimmunization of donors or hosts did not prevent the suppression; the grafting of irradiated donor-type spleen cells (source of "accessory" cells) produced only an additive effect. Parental marrow and thymus cells were able to generate new precursors of PFC and specific inducer cells, respectively, in spleens of F(1) hybrid mice, as detected by two-step experiments utilizing parent-strain secondary recipient mice. The suppression depended upon transferring parental strain thymus cells into F(1) hybrid mice and was seen irrespective of the marrow donor strain. When irradiated mice were immunized twice (on the day of transplantation and 4 days later), there was only marginal suppression of antibody production when marrow cells only or marrow plus thymus cells were transplanted. Thus, it appears that an excess of thymus-derived "suppressor" cells is generated upon exposure to alloantigens and inhibit terminal differentiation of antibody-forming cells in a noncytotoxic manner. Mature PFC themselves were not the targets of suppression. The method of immunization probably determines the relative functional capacity of thymus-derived "helper" and suppressor cells.

The role of thymocytes and bone marrow cells in defining the response to the dinitrophenyl hapten attached to positively and negatively charged synthetic polypeptide carriers. Cell fractionation over charged columns

An inverse relationship exists between the net electrical charge of immunogens and the antibodies they elicit (1). Results of an earlier study have demonstrated that the net charge phenomenon has a cellular basis, since the immune response potential of murine spleen cells to 2,4-dinitrophenyl (DNP) on a negatively charged synthetic polypeptide carrier was reduced by cell fractionation over negatively charged glass beads, whereas the response to the same hapten on a positively charged carrier was unaffected (14). To verify that the net charge correlation is expressed at the cellular level, spleen cells were fractionated over positively charged poly-L-lysine-coated glass bead columns, and their immunocompetence to DNP on positively and negatively charged carriers was tested by cell transfers in irradiated recipient mice. In this case, the fractionated cells showed reduced response potential to DNP on the positively charged carrier only. Thus, the cellular basis of the net charge phenomenon has been demonstrated for both positively and negatively charged immunogens (for the same specificity) by cell separation techniques over columns of opposite charge. In order to establish whether the cell population relevant for the charge properties of immunogens was of thymus or marrow origin, thymocytes and bone marrow cells were selectively passed over positively or negatively charged columns and mixed with unfractionated cells of the complementary type. Transfers of the filtered and unfiltered cell mixtures in irradiated recipient mice immunized with DNP on either a positive or a negative synthetic polypeptide carrier indicated that fractionation of thymocytes, but not of marrow cells, correlated with the spleen population. Thus, thymocytes fractionated over negatively charged columns and mixed with unfractionated marrow cells exhibited reduced response to DNP on the negative carrier, but normal responses to DNP on the positive carrier. The opposite result was obtained when thymocytes were passed over positively charged columns. No effect on the anti-DNP response was detected by filtration of bone marrow cells over columns of either charge. These findings indicate that it is possible to distinguish between thymocytes on the basis of their capacity to react with more acidic or more basic surfaces and that a population of thymus-derived cells may recognize immunogens on the basis of their overall electrical charge. No evidence was found by these techniques that marrow-derived cells contribute to the net charge phenomenon.

Regulation of antibody response by cells expressing histamine receptors

Spleen cells from immunized and unimmunized mice were either passed over histamine-rabbit serum albumin-Sepharose columns or rabbit serum albumin-Sepharose control columns. The immune response potential of 5 x 10(6) cells excluded from the two columns were compared with each other, and with an equal number of unfiltered cells by injection of the cell suspensions mixed with sheep erythrocytes into irradiated, syngeneic recipients. The direct and indirect anti-sheep erythrocyte plaque-forming cell responses generated by the cells passed over the histamine-bead column were significantly greater than the responses resulting from the inocula of unfiltered cells or cells passed over control columns. These results indicate the existence of a cell population expressing surface receptors for histamine, which functions to regulate antibody responses.

Thymus-independence of slowly metabolized immunogens

The role of thymus in antibody responses to a series of four synthetic polypeptide immunogens of the general formula multi-copoly(Tyr,Glu)-poly(Pro)-poly(Lys) was investigated as a function of the optical activity of the amino acids composing their structure. Irradiated nonthymectomized and thymectomized SJL mice were injected with thymocytes, marrow cells, or a mixture of both. Each group of recipients was immunized with the following copolymer enantiomorphs: all L-amino acids; L-amino acids outside and D inside; D-amino acids outside and L inside; or all D-amino acids. The antibody response to the immunogen composed of all L-amino acids was thymus-dependent, whereas the responses to the other three copolymers were all independent of the thymus. Similar cell transfers were performed in DBA/1 mice immunized with multi-copoly(L-Phe,L-Glu)-poly(D-Pro)-poly(D-Lys). This mouse strain produces specific antibodies against the (Phe,Glu) region and against the poly(D-prolyl) region. The immune response to the determinant with only L-amino acids on the outside was thymusdependent, whereas the response to the inside immunopotent region with only D-amino acids was thymusindependent. Since earlier studies have demonstrated that synthetic polypeptide antigens that contain D-amino acids are poorly metabolized, the thymus-independence of the antibody responses to these multichain synthetic polypeptides that possess repeating antigenic determinants was correlated with the metabolizability of the immunogens or their component determinants.

Cytodynamics of the immune response in two lines of mice genetically selected for "high" and "low" antibody synthesis

Two lines of mice have been separated by selective breeding for the character "agglutinin production to heterologous erythrocytes." Around the 18th generation of selection the two lines could be considered as homozygous for the character investigated. This trait is under the control of a group of additive genes. The interline difference in the production of anti-SE agglutinins was verified for the range of antigen doses from subimmunogenic to maximal. After intravenous immunization with an optimal dose of SE, the duration of the exponential rise in serum antibody was 4-5 days in both lines. At this time most of the interline difference in responsiveness is already expressed. A cytodynamic study carried out in terms of plaque-forming cells (PFC) and rosette-forming cells (RFC) in the spleen during the exponential phase showed that the principal interline difference is found in the doubling time of cells engaged in the immune response. More precise cytodynamic analysis made in terms of RFC showed that the doubling time of RFC is 9 hr in high responder and 16 hr in low responder mice. The duration of the exponential rise and the number of target cells stimulated by antigen is the same in both lines. The interline difference at the end of the exponential rise (4 days postimmunization) is larger in terms of serum antibody (30-40-fold) than in terms of PFC or RFC (20- and 11-fold, respectively). A morphological study of RFC in nonimmunized mice showed that about 90% of rosettes were formed by small lymphocytes in both lines. The remainder were medium-sized lymphocytes. At the peak of the cellular response the RFC have differentiated into large lymphocytes, blast cells, and plasma cells. The contribution of plasma cells to RFC is much greater in the high than in the low line. The cytodynamic and morphologic results presented in this article are compatible with the hypothesis that the group of genes segregated in each line during the selective breeding control and regulate the rate of multiplication and differentiation of the antibody-producing cells.

The effects of ALG on the murine immune response to sheep erythrocytes

Antilymphocyte globulin (ALG), and to a lesser extent normal rabbit globulin (NRG), when given to mice prior to immunization with sheep-RBC suppress both the γM and γG_2a responses. Globulin injected after the antigen suppresses the γG_2a response, augments the γG₁ response and has little effect on the γM response. These effects are also observed in mice partially paralysed to rabbit γ globulin. In another system—the response to hapten—protein conjugates precursors of antibody producing cells were found to be more resistant to ALS treatment in vivo than were helper cells. It is concluded that the suppressive effects of ALG treatment are largely due to the direct action of ALG on helper cells (T-cells). The mechanism of the adjuvant-like effect is unclear.

Antigen-specific cells in mouse bone marrow. II. Fluctuation of the number and potential of immunocyte precursors after immunization

Quantitative and qualitative changes of mouse bone marrow cells were studied by limiting dilution assays 2-3.5 months after immunization of donors with sheep erythrocytes or unrelated antigens (Salmonella typhimurium, horse and chicken erythrocytes). Irradiated (C3H x C57BL/10)F(1) mice were reconstituted with an excess of nonprimed thymocytes and small graded numbers of primed bone marrow cells. Direct and indirect plaque-forming cells (PFC) were induced by secondary stimulation with SRBC and enumerated on the 9th day after cell transplantation. Marrow precursors of PFC (P-PFC) cooperated with thymocytes in the production of direct and indirect PFC after SRBC priming. The limiting dilution plots, which were not compatible with predictions of the Poisson model before immunization, changed and conformed to this model afterwards, as if the population of P-PFC had become functionally more homogeneous. The concentration of marrow P-PFC increased up to the 3rd month after priming, and decreased during the 4th, varying over two logarithms of nucleated marrow cells. The fluctuation was simultaneous and of the same order of magnitude for precursors of direct and indirect PFC, which were class restricted. A third effect of immunization was detected at 3.5 months: individual precursor units generated 3-4 times more direct and indirect PFC than at earlier intervals. Qualitative and quantitative changes of marrow P-PFC participating in anti-sheep responses were specific, since antigens unrelated to SRBC failed to induce them. The data suggested that marrow-derived cells were the major carriers of immunologic memory, but that they functioned in cooperation with thymus-derived inducer cells during secondary anti-sheep responses.

Requirement for continuous antigenic stimulation in the development and differentiation of antibody-forming cells: effect of antigen dose

The concept that antigen has a continuous role in the recruitment and differentiation of immune progenitor cells was tested with optimum and suboptimum doses of heterologous erythrocytes in mice. These studies further evaluated an immune cell maturation scheme in which continuous antigenic stimulation is required for both the recruitment of `antigen-sensitive units' and the expansive proliferation of a distinct sensitized cell compartment, which undergoes irreversible differentiation to functional antibody-forming cells. Haemolytic plaque-forming cell capacity during both the primary and secondary immune reactions were studied, both in the intact animal and with the spleen cell transfer technique. This in vivo culture technique was used to measure the sensitized cell compartment in the absence of existing antibody regulatory mechanisms. The results clearly demonstrate a higher detectable secondary immune capacity in the suboptimum antigen dose group than in the optimum antigen dose group. This was demonstrated for both the 19S and 7S cellular responses, as well as with humoral antibody levels measured in the spleen cell recipient mice. It can be concluded that in the presence of a suboptimum dose of antigen, which rapidly diminishes during the early intervals of the primary response, there is adequate recruitment with subsequent preservation or rescue from antigen-mediated depletion of the sensitized cell compartment, at the expense of the detectable primary response.

Density gradient separation of marrow cells restricted for antibody class

Primitive cells of (C3H x C57BL/10)F(1) mouse bone marrow, participating with thymocytes in immune responses to sheep erythrocytes, are already committed to the immunoglobulin M or immunoglobulin G antibody class. By equilibrium centrifugation in discontinuous gradients of bovine serum albumin, cells responsible for production of IgM immunocytes migrate to the denser regions, whereas those responsible for IgG immunocytes remain in the lower density regions.