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

Histamine-binding suppressor T cells in rabbit peripheral blood

Peripheral blood leukocytes (PBL) from primed rabbits were able to suppress the in vitro anti-sheep red blood cell (SRBC) plaque-forming cell (PFC) response of autologous spleen cells. A population containing the suppressor cells could be isolated from PBL by cell fractionation on columns of insolubilized histamine. In contrast to spleen cells, PBL generatd a weak secondary anti-SRBC response in vitro. A strong response was obtained with PBL freed from histamine-binding (H+) cells. The addition of these H+ cells to cultures of H-PBL caused strong suppression. The H+ suppressor cell was further characterized as a radioresistant T cell. Low-dose irradiation of H- cells resulted in a supplementary enhanced PFC response suggesting that PBL also contain a radiosensitive regulator cell which is not histamine binding.

Macrophage-lymphocyte interactions mediated by soluble factors

Adherent-cell-depleted primed rabbit splenocytes were capable of mounting an in vitro response to SRBC. The addition of alveolar macrophages (AM) to adherent-cell-depleted or unseparated lymphoid cell populations resulted in significant suppression of the PFC response. Suppressive activity was limited to AM and dependent on the presence of a ratio of 1 AM:20 lymphocytes. The cell-mediating suppression was found to be resistant to irradiation and antithymus globulin but sensitive to heat, freeze-thawing, and treatment with iodoacetamide. Suppression was mediated by a soluble factor (MW greater than 10,000 daltons) that required an AM-lymphocyte interaction for its production. Suppression appeared to be achieved through the inhibition of proliferation of antigen sensitive cells although the effect of AM could possibly be exerted on an early event in the immune response. AM were capable of enhancing the proliferative responses of rabbit lymphoid cells to PHA and Con A. Enhancing and suppressing activities of AM were abolished by inhibition of RNA synthesis but unaffected by inhibitors of DNA and protein synthesis.

Aberrant secondary antibody responses to sheep erythrocytes in rabbits with experimental syphilis

Rabbits infected with Treponema pallidum have strikingly depressed in vivo immunoglobulin G responses to sheep erythrocytes. To gain further insight into the nature of this suppression, the immune responses of splenic and peripheral blood lymphocytes from infected rabbits to sheep erythrocytes were studied in vitro. Spleen cells from rabbits that had been sensitized with sheep erythrocytes during active syphilis had greatly decreased immunoglobulin M and G responses after in vitro incubation with sheep erythrocytes, when compared to the results obtained with cells from sensitized uninfected animals. Suppressor cells could be demonstrated in peripheral blood lymphocytes of control rabbits 6 months after sensitization with sheep erythrocytes; these cells could be removed by nylon wool filtration. When primary sensitization with sheep erythrocytes was carried out during active syphilis, these suppressor cells were not detectable in peripheral blood lymphocytes 6 to 9 months later. These findings provide further evidence that induction of immune responses may be abnormal early in treponemal infection and may help to explain the failure of the host to produce antibodies which eradicate the organism during the first 2 to 3 months of infection.

Responsiveness of rabbit spleen and appendix cells to bacterial mitogens

Rabbit spleen and appendix cells were used to test the mitogenic activity of a commercial lipopolysaccharide (LPS) preparation from Salmonella typhimurium (Difco), a preparation extracted from it, and cell wall preparations from smooth (45/0) and rough (45/20) strains of Brucella abortus. On the basis of [3H]thymidine incorporation ratios (E/C), that is, the incorporation rate among cells treated with the mitogen relative to that of untreated cells, the extracted LPS and both Brucella cell wall preparations, but not the commercial LPS were potent mitogens for rabbit spleen cells. By the same criterion, only the Brucella cell wall preparation produced a significant, but minimally so, response among appendix cells. The weak responsiveness of appendix cells may be more apparent than real, however, and may not imply a difference in intrinsic susceptibility to mitogens by these two populations, because unstimulated appendix cells incorporated thymidine at 10 times the rate of unstimulated spleen cells. Appendix cells, then, may not be susceptible to further stimulation, even by active mitogens. Therefore, the significance of E/C ratios may be equivocal when materials are assayed for mitogenic activity on lymphoid populations whose basal activity is relatively high.

Suppressor cells in rabbit peripheral blood

Rabbit peripheral blood leukocytes (PBL) added to cultures of autologous spleen cells, primed in vivo to sheep red cells, are able to suppress with high efficacy the secondary in vitro response of the spleen cells to that antigen. Removal of nylon wool adherent cells from PBL abolishes the suppressive effect. When the PBL are fractionated by velocity sedimentation the suppressor cells can be separated from the responding cells. The circulating lymphocytes, freed from the inhibiting effect, either by nylon wool absorption or by velocity sedimentation fractionation, are able to give a strong secondary in vitro anti-SRC response, in which the long latency period, usually observed when PBL are stimulated with antigen in culture, is abolished or at least reduced. The suppressor effect present in the PBL is not due to granulocytes, platelets or erythrocytes.

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

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

Immune response restoration with macrophage culture supernatants

Depression of the in vitro immune response of mouse spleen cell suspensions to sheep erythrocytes by removal of macrophages can be reversed by the addition of supernatants from peritoneal macrophage cultures. Supernatant activity can be absorbed by the red cell antigen, and supernatant-treated red cells are stimulatory in the absence of macrophages or supernatant.

Radioresistance of the enhancing effect of cells from carrier-immunized mice in an in vitro primary immune response

The in vitro primary response of mouse spleen cell suspensions to 2,4,6-trinitrophenyl(Tnp)-erythrocytes has been studied. The number of anti-Tnp plaque-forming cells that arise after antigenic stimulation in vitro is greatly enhanced by prior immunization in vivo with the carrier erythrocyte. The enhancement is antigen specific. The priming for an enhanced response can be elicited with very low antigen doses and is often apparent 24 hr after immunization. It is marked from day 3 to day 14. Spleen cells from carrier-primed mice will enhance the anti-Tnp response of normal cells when mixed cultures of the two cell populations are challenged with Tnp-erythrocytes in vitro. The carrier-primed cells mediating this enhancing effect are thymus derived. The development of the thymus-derived, carrier-specific cell population has been generally assumed to involve the antigenic stimulation of cell proliferation. It was, therefore, somewhat surprising to find that the enhancing effect of the carrier-primed cells, once they had been generated, is not inhibited by x-irradiation.