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

Suppression of the immune response

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Immune responses in vitro. 3. Development of primary gamma-M, gamma-G, and gamma-A plaque-forming cell responses in mouse spleen cell cultures stimulated with heterologous erythrocytes

We have demonstrated for the first time that mouse spleen cells stimulated in vitro with heterologous erythrocytes developed immunoglobulin class-specific gammaM, gamma(1), gamma(2a+2b), and gammaA plaque-forming cell (PFC) responses. A modification of the hemolytic plaque technique, the addition of goat anti-mouse micro-chain antibody to the assay preparation, specifically prevented development of all gammaM PFC and enabled accurate and reproducible enumeration of immunoglobulin class-specific PFC after treatment with appropriate monospecific anti-globulins and complement. Culture conditions, with regard to medium, atmosphere, agitation, and spleen cell densities, were similar to those previously shown to support only gammaM PFC responses. Evaluation of the kinetics of appearance of PFC showed that gammaM PFC reached maximum numbers on days 4-5; the magnitude of this response was 3-10 times greater than gamma(1) gamma(2a+2b), or gammaA PFC which reached maximum numbers on days 5-6. Optimal erythrocyte antigen dose for gammaM PFC responses was 10(7)/culture, whereas a dose of 10(6) erythrocytes/culture consistently stimulated optimal gamma(1) gamma(2a+2b), or gammaA PFC responses. Investigations of the effects of anti-erythrocyte antibody on gammaM and gammaG PFC responses indicated that antibody suppressed these responses by neutralizing the effective antigenic stimulus at the macrophage-dependent phase of the response. At the same antibody concentration, gammaG PFC responses were more effectively suppressed than gammaM PFC responses. Further, gammaG responses could be almost completely suppressed by antibody as long as 48 hr after initiation of cultures, whereas gammaM PFC responses could only be completely suppressed during the first 24 hr. These results were discusssed in terms of the role of antigen in the stimulation gammaM and gammaG antibody.

Participation of three cell types in the anti-sheep red blood cell response in vitro. Separation of antigen-reactive cells from the precursors of antibody-forming cells

Spleen cells of unprimed CBA mice were shown to produce anti-sheep red blood cell antibodies comparable in amount in vivo and in vitro. Under identical culture conditions spleen cells of C57BL mice did not respond. CBA spleen cells, passed through columns of cotton wool (CBAf), were equally inactive in vitro. However combined cultures containing both CBAf and C57BL cells yielded as many or more plaque-forming cells than the same number of unfractionated CBA spleen cells. Analysis of the contribution of each cell population to the synthesis of antibody in the combined cultures has disclosed the participation of three cell types. A thymus-dependent, radiosensitive cell was derived from the CBAf population, while the C57BL was the source of the precursor of the antibody-forming cell and of a radioresistant cell. The latter two were partially separated in a Staput apparatus.

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.

In vitro-initiated secondary anti-hapten response. II. Increasing cell avidity for antigen

Decreasing antigen in vivo may preferentially stimulate cells with the potential for synthesis of high-affinity antibody through activation of surface receptors with similarly high affinity. This selection should result in cells with increased sensitivity to lower antigen concentrations, cells with greater avidity for antigen. We have followed the in vivo changes in anti-TNP memory-cell sensitivity by initiating the secondary anti-hapten response in vitro. This response was determined by anti-TNP plaque assay. The results indicate that cell populations with increased sensitivity for antigen continue to emerge with time after priming and that this sensitivity may increase 1000-fold in a 4 month period. Increased sensitivity to stimulation by antigen is concomitant with suppression by higher, previously stimulatory doses as in high zone immune tolerance. The data support the hypothesis that memory cells of high avidity result from the selective pressure of diminishing in vivo antigen concentration.

Synergistic interaction of macrophages and lymphocytes in antigen-induced transformation of lymphocytes

The role of macrophages and lymphocytes in antigen-induced transformation of lymphocytes has been investigated. Lymphocytes and macrophages were obtained from inbred strain 13 guinea pigs which were either unimmunized or immunized with complete Freund's adjuvant (CFA) or tetanus toxoid in CFA. The transformation response to PPD or tetanus toxoid was assayed by tritiated thymidine incorporation. Addition of macrophages to immune lymphocytes significantly increased their response to purified protein derivative (PPD) or tetanus toxoid. This was observed if the macrophages were (a) "immune" or "nonimmune", (b) unirradiated or irradiated (3000 R), (c) 99% pure, and (d) peritoneal or alveolar in origin. Neither immune nor nonimmune macrophages were able to induce nonimmune lymphocytes to respond to PPD or tetanus toxoid. When macrophages were incubated with PPD or tetanus toxoid and then washed, they stimulated immune lymphocytes to transform. An incubation time of (1/2) hr was adequate, however, 2-4: hr was optimal. These studies indicate (a) that antigen-induced transformation of lymphocytes is greatly enhanced by macrophages; (b) that macrophage-antigen interaction can antecede lymphocyte-antigen interaction and results in macrophages which are able to stimulate lymphocyte transformation; and (c) that the immunological memory requisite to elicit specific transformation responses is a property of the lymphocyte and not the macrophage.

Maturation of hemolysin-producing cell clones. II. The appearance and localization of precursor units in lymphoid tissues of neonatal mice

Cells capable of reacting with sheep erythrocyte (SRBC) antigen to maturate and produce hemolysin appear simultaneously in the bone marrow and spleen of 1-day old Swiss-Webster mice. However, hemolysin-producing cell clones (HPCC) do not result. Complete functional precursor units generally appear in the spleens of mice older than 3 days. In vivo and in vitro data correlate well in this regard. Complete precursor units are not seen in the bone marrow and only very rarely in the thymus. The efficiency of precursor units of neonatal mice when they become functional approximates that of the mature animal when based on the doubling time of plaque-forming cells (PFC). Possible explanations of the initial appearance of incomplete precursor units have been discussed.

Peyer's patches: immunologic studies

The immune capabilities of the Peyer's patches have been investigated by the use of an in vitro system. Despite our failure to stimulate Peyer's patch lymphocytes in vivo it appears that Peyer's patches behave immunologically as peripheral lymphoid tissues. Cultures prepared from the dissociated Peyer's patches of normal rabbits respond to sheep erythrocytes. The response is comparable to that obtained with spleen cultures from the same animals and is not dependent on the presence of the epithelial cells which line the lumen. Similar thymic cultures do not respond. Our experiments with cultures prepared from rabbits which have received one or two injections of SRC show that the Peyer's patches contain both IgM and IgG "memory" cells which have migrated from the spleen. The concentration of these cells in the spleen remains several hundredfold higher.

The proliferative and anamnestic antibody response of rabbit lymphoid cells in vitro. II. Requirement for adherent and nonadherent cells of the responses to particulate antigens in spleen cell cultures

Both primary and secondary responses to sheep erythrocytes and to Brucella abortus antigen have been obtained in cultures of dispersed rabbit spleen cells. Removal of adherent cells by repeated incubation of spleen cells on absorbent cotton diminished the ability of the spleen cell suspensions to give secondary as well as primary responses in vitro. When comparing cultures made in dishes and in tubes, the loss of responsiveness after incubation on cotton was much more evident in the dish cultures. It was concluded that the cell-to-cell interaction needed for immune responses to particulate antigens in vitro was more readily interfered with when the cells were spread over a larger surface area. The proliferative response to antigen, as measured by uptake of (3)H-thymidine in tube cultures of the sensitive spleen cells, appeared particularly resistant to the depletion effect of adherent cell removal. Dispersed spleen cells from sensitized mice gave a secondary response to sheep erythrocytes. This response was readily abolished by one incubation on absorbent cotton when the cells were cultured in dishes.

Immune response in vitro: independence of "activated" lymphoid cells

Antibody formation against sheep erythrocytes by mouse spleen cells in vitro requires interactions among antigen-treated macrophages and lymphoid cells in cell culsters for only a finite time. During this critical period of interaction, lymphoid cells become "activated" and thereafter can develop into antibody-producing cells independently of native antigen, macrophages, and cell clusters.

Immune responses in vitro. II. Suppression of the immune response in vitro by specific antibody

The effects of hyperimmune anti-sheep erythrocyte (SRBC) antibody on the plaque-forming cell (PFC) response to SRBC by mouse spleen cells in vitro were studied. Anti-SRBC antibody specifically suppressed the PFC response against SRBC. The degree of suppression was directly related to the amount of antibody added and was overcome by large amounts of antigen. Suppressive activity was absorbed from the sera by SRBC and could be partially eluted from the antigen by heat. The PFC response in cultures stimulated with antigen-antibody complexes prepared with high concentrations of antibody were suppressed; however, some complexes prepared at lower antibody concentrations stimulated greater responses than SRBC alone. Antibodies collected after four immunizations had greater suppressive ability than those collected after two immunizations. The degree of suppression was as great whether antibody was added at the initiation of the cultures or 24 hr later, suggesting that during the first 24 hr the culture system was antigen-dependent. Incubation of separated lymphoid cells with antibody did not impair their ability to develop a PFC response in vitro. However, if macrophages were incubated with antibody either before or after incubation with SRBC, the subsequent PFC response by lymphoid cells was suppressed. The data are consistent with the conclusion that antibody suppresses the PFC response in vitro by neutralizing the antigenic stimulus at the macrophage-dependent phase of the response.