Cell-mediated immune response in vitro. 3. The requirement for macrophages in cytotoxic reactions against cell-bound and subcellular alloantigens

Novel immunomodulators with pronounced in vivo effects caused by stimulation of cytokine release

Beta-1,3-D-polyglucose derivatives protect mice against otherwise lethal bacterial infections. This protective effect has been considered to be mediated through mononuclear phagocytes. By using radioactive labelling, we localized the beta-1,3-D-polyglucose derivatized microbeads (GDM) during the period following injection. The GDM was recovered mainly in the milky spots of the omentum. In animals treated with GDM, the total white cell number was significantly increased in peritoneal fluid of mice before and after challenge with E. coli. Bacterial counts in peritoneal fluid of GDM treated animals declined to zero after 24 h. In untreated animals there was a slight increase in bacterial counts until the animals died after about 12 h. Mouse peritoneal macrophages stimulated with GDM released significant amounts of IL-1 and PGE2. There was no significant release of TNF. Levels of IL-1 and PGE2 in peritoneal fluid increased significantly during the first 48 h after treatment with GDM. There was no increase of levels of TNF. After challenge with E. coli, the levels of IL-1, TNF, and PGE2 were significantly lower compared with control animals. In untreated animals the levels of IL-1 and TNF remained elevated until the animals died after about 12 h. These studies demonstrate that the raised levels of arachidonic acid metabolites after pretreatment with GDM or AG seems to inhibit the otherwise lethal elevation of IL-1 and TNF in body fluids which is seen in untreated animals.

Dynamics of blood components and peritoneal fluid during treatment of murine E. coli sepsis with beta-1,3-D-polyglucose derivatives. II. Interleukin 1, tumour necrosis factor, prostaglandin E2, and leukotriene B4

The influences of pretreatment with beta-1,3-D-polyglucose derivatives on levels of cytokines and arachidonic acid metabolites in body fluids in experimental peritonitis in mice are reported. Peritonitis was induced by an intraperitoneal injection of 10(8) live Escherichia coli. Pretreated animals survived the infection, untreated animals died about 12 h after inoculation with E. coli. Levels of IL-1 in plasma and peritoneal fluid, measured by cytotoxicity assay of the HT-2 cell line, increased significantly during the first 48 h after intraperitoneal treatment with beta-1,3-D-polyglucose-derivatized microbeads (GDM) or soluble, aminated beta-1,3-D-polyglucose (AG). After subsequent challenge with E. coli, the levels of IL-1 were significantly lower than in untreated animals. There was no increase in levels of TNF after treatment with GDM or AG, measured by cytotoxicity assay of the WEHI clone 13 cell line. After challenge with E. coli, TNF in plasma and peritoneal fluid was significantly lower compared with untreated animals. Both PGE2 and LTB4, measured by radioimmunoassay kits, were increased in peritoneal fluid after treatment with GDM and AG. After challenge with E. coli, PGE2 and LTB4 in peritoneal fluid increased to about half the concentration of infected control animals. Intraperitoneal injection of indomethacin to pretreated animals resulted in increased levels of IL-1 and TNF and decreased levels of PGE2 following challenge with E. coli. The levels of IL-1 and TNF remained elevated until the animals died after about 12 h. These studies demonstrate that the raised levels of arachidonic acid metabolites after pretreatment with GDM or AG seem to inhibit the otherwise lethal elevation of IL-1 and TNF in body fluids which is seen in untreated animals.

Accessory factors involved in murine T cell activation. Distinct roles of interleukin 6, interleukin 1 and tumor necrosis factor

Interleukin (IL) 6 was compared to other macrophage-derived products for its capacity to support the proliferation of accessory cell-depleted T cells. Monoclonal anti-IL6 antibodies were found to inhibit completely the "accessory activity" of macrophage supernatants, thus demonstrating the central role played by IL6 in T cell activation. IL6 was apparently more critical for initiating than in maintaining T cell proliferation because anti-IL6 antibodies lost all inhibitory activity when added late to the culture. Moreover, IL6 was not the only accessory factor required for optimal T cell proliferation. Using low-density cultures to minimize the number of contaminating accessory cells, we found that significant proliferation of CD4 cells was obtained only in the presence of both IL6 and IL1. In contrast, with CD8 cells substantial proliferation was obtained with IL6 alone. This response could, however, be enhanced by IL1. Tumor necrosis factor (TNF) and granulocyte/macrophage colony-stimulating factor showed no activity in these assays. The concentrations of IL1 and of IL6 required to support optimal proliferation were 10 pg/ml and 1 ng/ml, respectively. Analysis of the mechanisms underlying T cell activation by IL1 and IL6 indicated that both cytokines were required for optimal production of IL2 but that IL6 alone was sufficient to confer IL2 responsiveness. For CD8 cells, this effect was observed with doses of IL6 about 100 times lower than those required for the induction of IL2 secretion (0.001 vs. 0.1 ng/ml). TNF, which was not capable of inducing IL2 secretion, was also found to induce IL2 responsiveness but only at a concentration approximately equal to 1000 times higher than that of IL6. In accordance with these observations, IL6 and to a lesser extent TNF were found to enhance IL2R expression by CD8 cells. Interestingly, this enhancing effect was totally dependent on the presence of IL2.

Effect of anesthesia on the immune system: suppression of the immunogenic capacity of macrophages and of lymphocyte transformation

Experiments were carried out aimed at investigating the effects of anesthesia without surgery on certain functional components of the immune system. We observed that the immunogenic antigen-presenting capacity of mouse peritoneal macrophages was significantly reduced one week post-anesthesia, with either injected or inhaled anesthetic drugs. On the other hand, an augmentation of the phagocytic activities of these macrophages was manifested. Hence, the impaired immunogenic potency could not be attributed to a reduced antigen uptake. Lymphocyte transformations, i.e., response to PHA and Con A were suppressed, whereas the response to LPS was augmented.

Lymphocyte phenotypes in cervical intraepithelial neoplasia and human papillomavirus infection

Lymphocyte phenotypes in cervical mucosa were studied using a panel of monoclonal antibodies. T lymphocytes were predominant both within the epithelium and in the subepithelial stroma. In the normal cervix, both the T4+ (helper/inducer) and T8+ (suppressor/cytotoxic) subsets were present in a ratio similar to that in the peripheral circulation. In human papillomavirus (HPV) infection and cervical intraepithelial neoplasia (CIN) there was depletion of intraepithelial lymphocytes, especially of T4+ subset, with reversal of the ratio of T4+ to T8+ subsets to less than one. In contrast, there was no significant reduction in the number of lymphocytes in the subepithelial stroma. Tac+ (antigen primed and clonal expanding) lymphocytes were absent both within the epithelium and in the subepithelial stroma. These findings support our suggestion that there is a localized immunodeficiency in HPV infection and CIN. The aetiological and therapeutic implications are discussed.

Detection of rearranged T cell receptor beta-chain gene and induction of cytolytic function in interleukin 2-responsive day 14-15 murine fetal thymocytes

A subpopulation of interleukin 2 (IL 2) receptor-positive day 14-15 murine fetal thymocytes can be induced by recombinant IL 2 to proliferate over prolonged time periods in dissociated cell cultures. The proliferating day 14-15 fetal thymocytes exhibit no cytolytic effector function, nor do they rearrange T cell receptor beta chain genes. This contrasts with thymic organ cultures in which day 14-15 thymocytes do rearrange beta chain genes and give rise to immunocompetent cells. However, such events can also take place in dissociated cell cultures, provided the IL 2-responsive thymocytes are cultured on syngeneic feeder cells in the presence of IL 2 and the mitogen concanavalin A. Under such conditions rearrangement of the beta chain gene complex becomes detectable and cytolytic effector cells are generated. The frequency of inducible cytolytic precursor cells in day 14-15 thymocytes is 1/7000. These data either imply that immunocompetent cells are already present in the day 14-15 fetal thymus, or differentiation from precursors to immunocompetent cells must occur in dissociated cell cultures.

Regulation of the cytotoxic activity of alloreactive cytotoxic T lymphocytes by helper cells and lymphokines

The cytotoxic activity of alloreactive cytotoxic T lymphocytes (CTL) was maintained and augmented by transferring cells from a 5-day mixed lymphocyte culture MLC into a host culture (HC) containing indomethacin, freshly explanted normal spleen cells, and peritoneal cells which were syngeneic to the MLC cells. The MLC cells used in the transfer experiments were generated by culturing untreated H-2b splenic responders with irradiated H-2d stimulators, or were generated by culturing Lyt-2-depleted H-2b splenic responders with irradiated H-2d stimulators. The allo-CTL were found to be derived from the donor MLC (first culture) when unfractionated MLC cells were transferred into a host (second) culture and incubated for 5 days. In contrast, the allo-CTL were derived from host culture cells when Lyt-2-depleted MLC cells were transferred and the combined cultures incubated for 5 days. In the former case, the augmentation of MLC-derived cytotoxicity did not result from nonspecific expansion of all donor T cells; instead it was mediated by lymphokine(s), distinct from IL-2, produced by helper T cells generated in host culture, which appeared to selectively expand the antigen-specific CTL or to increase the cytotoxic activity of these CTL. The helper T cells were Thy-1+, L3T4+, and Lyt-2-. These findings indicate that antigen-nonspecific help was provided by helper cells or helper factors (lymphokines) generated in the host culture, which maintained and augmented the cytotoxic activity of the fully generated allo-CTL. This helper effect was also seen in the induction of primary allo-CTL responses which could be generated with fewer stimulating cells and with a stronger cytotoxic response at different R/S ratios tested. The generation of allo-CTL in second culture following transfer of Lyt-2-depleted MLC cells to host cultures appears to have involved antigen carryover from the MLC; however, antigen carryover alone was not sufficient. It appears that in the absence of Lyt-2+ suppressor T cells, antigen-specific help might be generated in donor cultures (Lyt-2-depleted MLC) which promoted or recruited the generation of antigen-specific CTL in host culture.

The mechanism of antigen presentation by dendritic cells and splenic adherent cells in the induction of an allogeneic cytotoxic T-lymphocyte response to H-2Kk liposomes

Induction of an allogeneic cytotoxic T-lymphocyte (CTL) response to purified alloantigen is partially dependent on uptake and processing of the class I alloantigen by antigen-presenting cells (APC) followed by recognition of the alloantigen and self Ia by helper T cells (TH). The activated TH provides the helper signal(s) to the alloantigen-specific CTL for proliferation and differentiation into an active effector CTL. The role of antigen processing and presentation of major histocompatibility complex alloantigens was examined and the ability of different types of APC to present purified H-2Kk liposomes was investigated. Splenic adherent cells (SAC), splenic dendritic cells (DC), and B-cell lymphoblastoid lines were all shown to be effective in the presentation of H-2Kk liposomes. The relative ability of these cells to serve as APC was determined to be DC greater than B-cell tumors greater than SAC. The role of processing of H-2Kk liposomes by SAC and DC was examined by investigating the effect of weak bases on pulsing of the APC. These experiments suggest that presentation of alloantigen by both SAC and DC involves a step which is sensitive to inhibition by weak bases. We examined whether the TH were activated by similar mechanisms when stimulated by the various APC. The functional involvement of the T-cell surface marker L3T4 was demonstrated in the induction of TH. In contrast, L3T4 was not involved in the subsequent generation of CTL since monoclonal antibody (MAb) specific for L3T4 was not effective in blocking CTL function in the presence of nonspecific T helper factor (THF). Similarly, Ia on the APC was shown to be involved in the stimulation of the TH pathway but not directly in the differentiation of the CTL. Thus, DC and B cells in addition to SAC can present H-2Kk to TH. The presentation of alloantigen by both cell types may involve an intracellular route as demonstrated by the blocking of the TH response by weak bases. Both Ia and L3T4 are required on the APC for induction of the TH response. The minimal requirements for activation of the CTL were H-2Kk liposomes and a source of THF.

Interleukin 2 induces both, growth and maturation of lectin reactive Lyt-2+ but not Lyt-2-precursor cells and regulates the cytolytic potential of effector cells

This study investigated the requirements for lymphokines derived by recombinant (rec.) DNA technology for the induction of growth and maturation in highly purified lectin reactive T cell subsets. Nylon purified C57BL/6 lymph node T cells were treated with monoclonal anti-Lyt-2.2 or anti-L3T4 antibodies and fluorescence labeled (FITC) anti-immunoglobulin antibodies and were positively selected into Lyt-2+ (L3T4-) and Lyt-2- (L3T4+) lymphocyte subsets using a fluorescence-activated cell sorter. Sorted T lymphocytes, which were devoid of accessory cells were incubated either in bulk culture (2 X 10(2) - 3 X 10(4) cells/microculture) or under limiting dilution conditions (2.5-1,000 cells/well) with lectin (Concanavalin A, Leukoagglutinin) and rec. human Interleukin 2 (rec. hIL-2) and/or rec. mouse Interferon gamma (rec. mIFN-gamma). The data show that Lyt-2+ lymphocytes respond to lectin and rec. hIL-2 with growth and development of cytolytic activity in the absence of other exogenous factor(s) or accessory cells. The presence of monoclonal antibodies to the Interleukin 2 receptor during the sensitization phase ablated the induction of Con A reactive precursor cells of cytolytic lymphocytes (CTL-P) by either rec. hIL-2 or conventional IL-2 containing lymphokine sources, indicating the essential role of IL-2 during activation of Lyt-2+ T lymphocytes. In contrast, Lyt-2- lymphocytes could not be induced by lectin and rec. hIL-2 alone for proliferation and always required the presence of accessory cells for significant growth. Exogenous rec. m IFN gamma was unable to induce growth and cytolytic activity in Con A reactive Lyt-2+ cells and did not significantly effect their response to rec. hIL-2. Limiting dilution experiments revealed that 10-16% of the Lyt-2+ lymphocytes responded to Con A and rec. hIL-2 with growth (GTL-P). The frequencies of CTL-P, determined under similar conditions, were always lower compared to GTL-P. However the results suggest that the differences observed between both precursor populations is due to differential sensitivity of the detection system rather than to the recruitment of distinct T cell subsets. Furthermore, it was shown that at least 50% of lectin reactive CTL-P were induced by rec. hIL-2 to secrete IFN-gamma under optimal conditions. The finding that some of the conventional lymphokine sources were superior to rec. hIL-2 in the induction of growth and cytolytic activity suggests the existence of mediators distinct from IL-2 that regulate the expansion of CTL-P.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of interleukin 1+ and interleukin 1- cell lines to dissociate signals involved in the induction of cytolytic T cells

The availability of paired homogeneous Ia+ tumour cell lines (P388AD, interleukin (IL)-1+, and P388NA, IL-1-), which differ in inducibility for IL-1, provided a unique opportunity to assess directly the role of Ia and IL-1 in the induction of cytolytic T cells (CTL) to trinitrophenol (TNP)-modified self. TNP-P388AD but not TNP-P388NA consistently induced H-2-restricted, hapten-specific CTL. However, in the presence of an exogenous source of IL-1, TNP-P388NA was able to induce CTL of the magnitude seen with TNP-P388AD. Both Ia expression and IL-1 secretion were necessary in that when TNP-modified purified T cells were utilized as stimulators, CTL activity was not demonstrated even if IL-1 was added, but was only seen when unmodified, P388AD, or spleen cells were added to the cultures.

Increase in proliferation and cytotoxic cell development in human mixed lymphocyte cultures in the presence of very low concentrations of LPS: role of IL-1 and prostaglandin E2

Lipopolysaccharide (LPS) added to human allogeneic mixed lymphocyte cultures (MLC), even at very low concentrations, increased the level of specific cytotoxicity that developed. Proliferation was also increased by LPS in MLC but no increase was detectable when the allogeneic stimulus was absent. LPS enhanced only low cytotoxic responses while having little effect on naturally high responses. Significant enhancement in cytotoxic response was found within the picogram-nanogram per milliliter range of concentrations of LPS and only when it was added at the initiation of cultures. This early action of low concentrations of LPS suggested that IL-1 was involved. Indeed, a supernatant from silica-treated human mononuclear cells containing IL-1 activity also enhanced cytotoxic and proliferative responses. Aside from increasing IL-1 secretion we also found that LPS significantly increased synthesis and secretion of PGE2 which had a selective inhibitory effect. Namely, addition of indomethacin or flurbiprofen to MLC further enhanced the cytotoxicity of LPS-treated but not that of untreated cultures without increasing the proliferative response. These results suggest a key role for macrophage-derived IL-1 and PGE2 in the regulation of proliferative and cytotoxic responses of T cells. They also suggest that very low amount of LPS may reach the immune system and contribute to the expression of cell-mediated immune responses.

Investigations into the mechanism of immunosuppression caused by acute treatment with O,O,S-trimethyl phosphorothioate. II. Effect on the ability of murine macrophages to present antigen

Acute administration of 10 mg/kg O,O,S-trimethyl phosphorothioate (OOS-TMP) for 24 h has been shown to suppress the in vitro generation of cytotoxic T lymphocyte responses and antibody-secreting cells to sheep red blood cells and to increase interleukin-2 production. Macrophages were shown to be the splenic cell population most affected by OOS-TMP pretreatment. In this report, the ability of macrophages from OOS-TMP-treated animals to function in antigen presentation was shown to be significantly decreased. In addition, macrophages from treated animals had increased phagocytic capability and interleukin-l production. However, the percentage of Ia-positive macrophages present in splenic populations was decreased following OOS-TMP treatment. A decrease in antigen presenting ability and the number of Ia-positive macrophages may explain the reversible suppression in cytotoxic T lymphocytes and antibody responses reported previously.

Recombinant interleukin 2 differentiates alloantigen-primed Lyt-2+ T cells into the activated cytotoxic state

The possibility of the generation of secondary cytotoxic T lymphocyte (2 degrees CTL) activity from alloantigen primed T cells by genetically homogeneous recombinant human interleukin 2(G-IL2) was analyzed. Not only purified IL2 by cell culture (C-IL2) but also G-IL2 induced 2 degrees CTL activity from primed T cells generated in mixed lymphocyte culture. This induction process required RNA and protein synthesis, while DNA synthesis was not relevant. In parallel to the induction of 2 degrees CTL activity, transition of the primed cells from the resting G1a to activated G1b has taken place. 2 degrees CTL activity was induced from nylon column-purified primed T cells in the absence of accessory cells and also in the absence of Lyt-1+ T cells. Interferon-gamma (IFN-gamma) induction was detected during the course of activation of alloantigen-primed T cells into the cytotoxic state. When IL2 was absorbed, IFN-gamma in the culture supernatant did not induce 2 degrees CTL activity. These results suggest that the IL2 molecule possessing T cell growth factor properties shares the nature of differentiation factor in terms of the activation of alloantigen-primed T cells into cytoxic state. The role of IFN-gamma produced in situ for this activation process awaits further investigation.

Human monocyte heterogeneity: interleukin 1 and prostaglandin E2 production by separate subsets

Human peripheral blood monocytes were separated into four different subpopulations by means of a discontinuous bovine serum albumin gradient. Of the least dense population, 7% were present in fraction A, 11% in fraction B, 28% in fraction C and of the most dense, 34% were in fraction D. The rest (17%) of the recovered cells sedimented as a pellet, of which 95% were dead. The monocytes of fraction D (= greater than or equal to 1.075 kg/l) were major interleukin 1 (IL 1) producers and their presence enhanced immunoglobulin synthesis in vitro. Fraction C (= greater than or equal to 1.070 kg/l) were the major prostaglandin E2 (PGE2) producers and demonstrated suppressor activity on in vitro IgG and IgM synthesis. Fractions A and B had minimal production of either IL 1 or PGE2 and lesser effects on the IgG and IgM synthesis. These data demonstrate functional heterogeneity of peripheral blood monocytes with respect to production of both IL 1 and PGE2 as well as accessory cells for immunoglobulin synthesis.

Epithelial cells expressing aberrant MHC class II determinants can present antigen to cloned human T cells

The first step in the induction of immune responses, whether humoral or cell mediated, requires the interaction between antigen-presenting cells and T lymphocytes restricted at the major histocompatibility complex (MHC). These cells invariably express MHC class II molecules (HLA-D region in man and Ia in mouse) which are recognized by T cells of the helper/inducer subset in association with antigen fragments. Interestingly, in certain pathological conditions, for example in autoimmune diseases such as thyroiditis and diabetic insulitis, class II molecules may be expressed on epithelial cells that normally do not express them. We speculated that these cells may be able to present their surface autoantigens to T cells, and that this process may be crucial to the induction and maintenance of autoimmunity. A critical test of this hypothesis would be to determine whether epithelial cells bearing MHC class II molecules (class II+ cells) can present antigen to T cells. We report here that class II+ thyroid follicular epithelial cells (thyrocytes) can indeed present viral peptide antigens to cloned human T cells.

The effect of age on the antigen-presenting mechanism in limiting dilution precursor cell frequency analysis

We have utilized limiting dilution analysis (LDA)2 to compare the intrinsic precursor cytotoxic T lymphocyte (pCTL) frequency for influenza-plus-self in young and old C57BL/6 mice. Under conditions of excess interleukin 2 (IL-2) and antigen presenting cells (APC) derived from spleens of mice matched in age to those being tested, we found more than a twofold difference in pCTL frequency between young and old animals. However, there was no difference in pCTL frequency between the two age groups if antigen was presented to the old responder cells on spleen cells derived from young mice. The apparent decrease in pCTL frequency in old mice by standard LDA may in fact be due to a defect in the antigen processing and/or presentation mechanism of old spleen cells. We conclude that the age-associated defective CTL activity previously reported by us and by others may be due at least in part to a defect in the antigen presentation mechanism of aging mice.

T cell clones interacting with accessory and T helper cells for a proliferative response

The requirement for cell interactions in T cell activation has been studied with two continuously in vitro growing T cell clones. These clones are specific for minor histocompatibility antigens, are H-2K restricted, and one clone is functionally a cytolytic T lymphocyte. Both can proliferate when interleukin 2 is added to the cultures, but for continuous growth they require irradiated spleen cells carrying the specific minor histocompatibility antigen and the restricting H-2. In this study we show that for proliferation the clones require at least two cell populations in the stimulator spleen, one is a splenic-adherent cell (SAC), the other a T cell. The SAC are plastic adherent, Thy-1-, Ia+. The T cells are nylon wool nonadherent, Thy-1+, Lyt-1+2- and Ia-. Cell mixing experiments of stimulator cells (all were done with H-2-syngeneic cells), depleted of either SAC or T cells confirm the requirement for a specific interaction between these two cell types and the T clone. Neither SAC, syngeneic with the T clone when mixed with T cells of the stimulator type, nor T cells syngeneic with the clone added to stimulator SAC, can induce an optimal proliferative response. Such a response is obtained only if both cell types, SAC and T cells, are of the stimulating genotype. This suggests that, in addition to an interaction of clonal T cells with SAC, a specific recognition at the T cell level between T stimulator and T clone is necessary. The interaction of the T clones with stimulator SAC and T cells leads to an activation, mediated by antigen recognition, of all three cell populations. Since we also show that each of the stimulator cell types are impaired by ultraviolet light irradiation, we conclude that factor production by SAC and T helpers is the final prerequisite for clonal expansion.

Enhancement of rat ACT-1 tumor clonogenicity by xenogeneic mouse macrophages

In vitro growth of rat atriocaval epithelial tumor cells (ACT-1) was enhanced by the inclusion of xenogeneic mouse adherent peritoneal exudate cells (PECs) in a two-layer soft agar system. A linear relationship was found between the number of cells plated and the number of colonies when ACT-1 tumor cells were plated at plating densities of between 1 and 5 X 10(5) cell/60 mm plate (r = 0.9, P less than 0.001). Inclusion of irradiated PECs in the bioassay for tumor stem cells resulted in a two and a half-fold increase in colony formation in three separate experiments (P less than 0.001).

Functional heterogeneity of human cord blood monocytes

Human cord blood monocytes were separated into four different subpopulations by means of a discontinuous bovine serum albumin (BSA) gradient. Of the least dense, 31% were present in fraction A, 17% in fraction B and 13% in fraction C and of the most dense, 20% were in fraction D. The rest (17%) sedimented as a pellet, of which 93% were dead cells. The monocytes of fraction C (density greater than or equal to 1.070) demonstrated suppressor activity on in vitro antibody synthesis of maternal B cells. Fraction D (density greater than or equal to 1.075) monocytes enhanced antibody synthesis of maternal B cells compared with synthesis produced in a similar experiment with unfractionated monocytes. Addition of either fraction A or B monocytes to the mixed culture of T and B cells resulted in antibody production comparable to that produced by addition of unfractionated monocytes. The functional heterogeneity of the cord monocytes was assayed also by 2-deoxyglucose (2-DOG) uptake, a marker for immunological macrophage activation. Fractions A and D showed significantly higher 2-DOG transport than that of unfractionated monocytes; in contrast, fraction C showed a 50% reduction of 2-DOG uptake. Furthermore, in contrast to fraction D, fraction C possessed only minimal phagocytic activity (for antibody-coated sheep erythrocytes) and minimal hemoxygenase enzyme activity. These data demonstrate functional heterogeneity of cord blood monocytes.

Interleukin-1 synthesis and activity in aged mice

Recent studies have provided evidence that deficient interleukin-2 (IL-2) production by helper T cells contributes to the impaired T-cell-mediated functions observed in aged mice. Since most of these responses depend upon the presence of macrophages, a deficit in the functional capacity or in cell cooperation of macrophages may result in a decrease in immune reactivity. We found in the present study, that in vitro the cytostatic activity of macrophages from aged C57BL/6 (B6) mice is affected only slightly, but that in vivo their number increases with age. The synthesis of IL-1 is reduced when macrophages from aged mice are stimulated in vitro by lipopolysaccharide, but addition of exogenous IL-1 apparently does not restore either the mixed lymphocyte reaction or cytotoxic T lymphocyte generation. Co-cultures of young splenic macrophages with aged T lymphocytes do not restore to normal level the impaired proliferative response to T mitogens of aged B6 mice, but aged splenic macrophages provide a full accessory help for mitogenesis of young T cells. Thus, absorption of IL-1 by phytohemagglutinin-activated T cells is slightly altered in aged mice. IL-2 responsive T cells are not altered since exogenous IL-2 supply in vitro completely reconstitutes cytotoxic T lymphocyte generation after an allogeneic stimulation. Moreover, the number of Lyt 1+ cells is not modified in aged B6 mice. These results suggest that the impaired capacity of macrophages to release IL-1 and of blast T cells to bind IL-1 may contribute to the depression of cell-mediated immune reactivity associated with aging but also that the main defect is a functional lesion of IL-2 production by Lyt 1+ helper T cells.

The effects of dichloro-trans-dihydroxy-bis-isopropyl-amine-platinum IV on the primary cell-mediated cytotoxic response

The effects of diamino-dichloro-cis-platinum II (DDP) and dichloro-trans-bis-isopropyl-amine-platinum IV (DDIP or CHIP) on the primary cell-mediated cytotoxic (CMC) response developed in a mixed lymphocyte tumor cell culture (MLTC) were investigated. DDP as well as CHIP added on day 0 augmented the CMC response when spleen cells from C57Bl/6 mice were cultured for 4 days with supraoptimal numbers of irradiated (4000 rads) allogeneic P815 mastocytoma cells. A similar effect was observed when mice were treated with either of the two platinum compounds 1 or 5 days prior to spleen removal and sensitization of the spleen cells in a MLTC. Augmentation was not observed at optimal or suboptimal R:S. When spleen cells were preincubated with CHIP, only inhibitory effects on the CMC response could be demonstrated. Decreasing Cl- -ion concentrations in the preincubation medium increased the inhibitory effect of CHIP. After CHIP administration to spleen donor mice, the development of antigen specific suppressor cells was inhibited only at doses higher than those required to inhibit the development of nonspecific suppressor cells. Spleen responder cells from CHIP-treated donors exhibited a lower sensitivity to both antigen-specific and nonspecific suppressor cells than spleen responder cells from untreated control donors.

Characterization of the cytotoxin produced by macrophages in response to dengue virus-induced cytotoxic factor

We have observed earlier that dengue type 2 virus-induced cytotoxic factor (CF) induces macrophages to produce a cytotoxin (CF2) which kills mainly the macrophages, some of the T lymphocytes and has no effect on B-lymphocytes of normal mouse spleen. The findings of the present study show that CF2 is heat-labile, trypsin-sensitive and unstable at acid and alkaline pH. It is a low molecular weight product as it is dialysable, non-sedimentable on ultracentrifugation at 103,500 g for 3 h and passes through 0.22 micron Millipore filter. It is adsorbed onto the target normal mouse spleen cells. The properties of CF and CF2 have been compared.

Immunoregulation of the mixed lymphocyte reaction by macrophage-derived factors: functional and biochemical separation of enhancing and inhibitory factors

Positive and negative immunoregulation of the mixed lymphocyte reaction (MLR) occurred through release of macrophage(MO)-derived, soluble enhancing and inhibitory factors. Macrophages, sonicated or cultured in low concentrations, produced nondialyzable, soluble factor(s) capable of enhancing the MLR; but the culture supernatant had no biologically detectable levels of Interleukin 1, Interleukin 2, or interferon. Production of enhancing supernatants was not affected by pretreatment of MO with trypsin or anti-Thy 1 antibody plus complement. In contrast, MO cultured in high concentrations yielded an inhibitory supernatant factor(s) which suppressed MLR reactivity even when MO were cultured in the presence of indomethacin. Culturing MO with proteolytic enzyme inhibitors increased the yields of the inhibitory and enhancing factors. Both factors were precipitable with ammonium sulfate and could be separated into several biologically active fractions using anion exchange chromatography.

Suppressive effect by cooperation of splenic and peritoneal adherent cells on generation of cytotoxic T lymphocytes

When spleen cells primed in vivo against allogeneic lymphoid cells were used as responder cells in secondary mixed lymphocyte cultures, a high degree of cytotoxicity was generated even in the absence of splenic adherent cells. However, removal of adherent cells from such primed responder spleen cells reduced the cytotoxicity to some extent. On the other hand, when these responder cells were transferred into the peritoneal cavity of irradiated syngeneic mice together with antigenic cells, unseparated responder cells generated a lower degree of cytotoxicity than did adherent cell-depleted responder cells. In an in vitro system, peritoneal adherent cells also suppressed the generation of cytotoxic T lymphocytes by unseparated responders; however they augmented the cytotoxic T lymphocyte generation by adherent cell-depleted responders. These adherent cell populations with augmenting activity became inhibitory when they coexisted. The mechanism of this inhibitory action remains unclear.

Concanavalin A stimulation of mouse lymphocytes at low concentration. I. The effect of peritoneal exudate cells

The results presented here show that concanavalin A (Con A) stimulated mouse spleen lymphocytes cultured at 1/10th optimal concentration incorporated less [3H]-TdR than those cultured at the optimal concentration. It was possible to increase the response of 1/10th optimal concentration lymphocytes by supplementing the cultures with macrophage-rich peritoneal exudate cell (PEC) preparations. This effect was dependent on the PEC concentration. [3H]-TdR incorporation by lymphocytes at optimal concentration was inhibited by the addition of PEC to the cultures. Thymocyte cultures at 1/10th optimal concentration also showed increased [3H]-TdR incorporation when supplemented with PEC but there was no inhibition effect at optimal concentration. PEC which had been pretreated with fresh mitomycin C to prevent cell division were as effective as controls at promoting the stimulation of 1/10th optimal concentration lymphocytes. PEC which had been killed were much less effective than controls.

Features of T cells causing H-2-restricted lethal graft-vs.-host disease across minor histocompatibility barriers

Evidence is presented that T cells that produce lethal graft-vs.-host disease (GVHD) to minor histocompatibility antigens (minor HA) comprise discrete subgroups of H-2K- and H-2D-restricted T cells; double negative selection of T cells in irradiated H-2 recombinant mice was used to separate these two subgroups. No evidence could be found that I-restricted T cells contributed to GVHD, either as effector cells or helper cells. The (unprimed) precursor cells for GVHD expressed the Thy-1+, Lyt-1+/-2, Ia- phenotype. Studies in which H-2-semiallogeneic bone marrow chimeras were used as hosts for negative selection suggested that presentation of minor HA to T cells during the induction phase is controlled by marrow-derived cells; indirect evidence was obtained that these latter cells can "process" minor HA presented on H-2 different cells and thereby render the antigens immunogenic. Studies in which minor HA-different, H-2-compatible chimeras were re-irradiated and then injected with donor-vs.-host T cells suggested that the effector phase of lethal GVHD involves contact of antigen on non-marrow-derived cells.

Lectin-dependent cell-mediated cytotoxicity following in vitro culture of normal lymphocytes in medium containing 2-mercaptoethanol

Cell-mediated cytotoxic reactivity resulting from the in vitro incubation of normal lymphocytes was assessed using nonspecific lectin-dependent cell-mediated cytotoxicity (LDCC) as a measure of overall reactivity. Spleen cells from non-immune C57BL/6 mice were incubated in vitro in RPM1-1640 supplemented with 10% fetal calf serum and 2-mercaptoethanol (2ME). Cytotoxicity was assayed against syngeneic Cr51-labeled EL-4 cells in the presence of Con A or PHA. Optimal LDCC was observed after 8 days of culture in the presence of 5 X 10(-5) M 2ME. Cytotoxicity was mediated by an activated T-lymphocyte population whose development did not appear to require macrophages. Usually LDCC in the presence of PHA was significantly greater than that obtained in the presence of Con A. The presence of 2ME during the initial phase of culture was crucial for the development of cytotoxicity, since early removal of 2ME after 1 or 3 days of culture did not alter the subsequent development of cytotoxicity, whereas delayed addition of 2ME on day 1 or 3 failed to produce cytotoxic reactivity. This rapid conversion from a 2ME sensitive state to a 2ME insensitive state may be related to a rapid loss of accessory cell viability during the early phase of culture. Together the results indicate that this system may provide a useful model for the investigation of the events leading to the development of CTL in vitro.

Comparative effects of 5'-amino-5'-deoxythymidine, a new antiviral agent, and 5-iodo-2'-deoxyuridine on the immune response of mice. No immunosuppression with 5'-amino-5'-deoxythymidine

Immunological function was analyzed in mice that received daily inoculations of 5'-amino-5'-deoxythymidine (1000 mg/kg/day, i.p.) or 5-iodo-2'-deoxyuridine (100 mg/kg/day, i.p.) following antigenic stimulation. 5' Amino-5'-deoxythymidine did not suppress the development of: (1) delayed type hypersensitivity response to sheep red blood cells, (2) cell-mediated cytotoxicity response to allogeneic tumor cells, and (3) IgM and IgG antibody response to sheep red blood cells. In contrast 5-iodo-2'-deoxyuridine suppressed the development of all of these responses.

Dept. of Microbiology, School of Medicine, East Carolina University, Greenville, NC

The responsiveness of spleen cells from C57BL/6J mice to various immunogenic stimuli was examined during the progressive growth of a poorly immunogenic fibrosarcoma T241. A strong correlation was observed between the progressive tumor growth and the depression of response to Concanavalin A, lipopolysaccharide, sheep red blood cells, and alloantigens in mixed lymphocyte reaction and cell-mediated lympholysis (CML). The maximum depression of these immune responses occurred when the animals had grown tumors for 3-4 weeks. Furthermore, serum from these animals collected 20 days after tumor transplantation was highly immunosuppressive. The possible mechanisms of tumor-induced immunosuppression have been discussed.

The inductive requirements for the primary in vitro generation of delayed-type hypersensitivity response to influenza virus in mice

Effector T cells (Td) which mediate delayed-type hypersensitivity reactions to influenza A virus can be generated in tissue culture using normal mouse spleen cells as the responder population. Addition of helper T cells enhances but is not essential for the production of Td cells. Both Ly 1 positive, I region restricted and Ly 2,3 positive, K,D region restricted effector cells are generated. Treating the responder cell population with anti-Ly 1 or anti-Ly 2,3 antibodies and complement prevented the generation of both classes of effector T cell, suggesting that the precursor Td cells are Ly 1,2,3 positive. Effector cells which are specific for the homologous virus or cross-reactive within the A strains of influenza virus are produced, as has been found previously in in vivo experiments. Depleting the cell population of phagocytic and plastic adherent cells resulted in a failure to produce Td cells, which showed a requirement for macrophage-like cells as accessory cells in the primary in vitro generation of Td cells. A variety of cells, such as peritoneal exudate cells, mitogen stimulated blasts or L929 fibroblast cells could serve as stimulator cells. Only Ly 2,3 positive, K,D region-restricted Td cells were produced when L929 cells were used as they lack I region-coded surface antigens. The I region-restricted DTH response was mapped to the IA sub-region of the H-2 gene complex.

Cellular interactions in the generation of cytolytic T lymphocyte responses. Analysis of the helper T cell pathway

Murine splenic lymphocytes exhibit a requirement for helper T cells for the induction of a cytolytic T lymphocyte response to suboptimal doses of allogeneic cells, membranes from allogeneic cells, or purified H-2 antigen in liposomes. The conditions where a requirement for help is apparent are the same conditions where a dependence on splenic adherent cells (SAC) has been demonstrated (Weinberger, O. et al., PROC. Natl. Acad, Sci, USA 1980. 77: 6091). Help can be provided in the form of primed, radioresistant, Ly-1+ spleen or lymph node cells or helper factor (interleukin 2, IL-2). A factor generated from phytohemagglutinin-stimulated human lymphocytes, when added to culture in the presence of antigen, bypassed the requirement for Ia+ SAC and helper cells. IL-2 reconstituted the response to H-2K(k) in liposomes in cultures depleted of SAC, strongly suggesting that the helper cell must see antigen re-expressed by an antigen-presenting cell, whereas the prekiller does not. IL-2 could be generated by culturing Ly-1+ murine spleen cells with H-2K(k) pulsed on SAC.

The peritoneal antigen-presenting macrophage: control and immunogenic properties of distinct subpopulations

The control of the immunogenic antigen-presenting capacity of different subpopulations of thioglycollate-induced peritoneal macrophages had been investigated. The experiments revealed the existence of two major subpopulations of macrophages, only one of which was highly efficient in educating antigen-specific T cells. The other subpopulation, while highly phagocytic, was devoid of antigen-presenting capacity. Further analysis, using specific antisera directed at H-2I region gene products, revealed that the immunogenic antigen-presenting population expressed H-2I region-controlled membrane antigens. Searching for cellular elements which control the differentiation of this antigen-presenting macrophage subpopulation, it was found that its function was strictly controlled by T cells. T cell-deficient mice (nu/nu) failed to generate a functional antigen-presenting macrophage subpopulation. Transplantation of mature T lymphocytes to T cell-deprived mice restored the immunogenic function of their antigen-presenting macrophage subpopulation. Transplantation of mature T lymphocytes to T cell-deprived mice restored the immunogenic function of their antigen-presenting macrophages. The results obtained suggest the existence of heterogeneity of functions among macrophage subpopulations and add a new regulatory function for T cells.

Antigen-presenting cell function in induction of helper T cells for cytotoxic T-lymphocyte responses: evidence for antigen processing

We demonstrate that splenic adherent cells (SACs) play an active role in the presentation of H-2Kk antigen for an alloreactive cytotoxic T-lymphocyte (CTL) response. If antigen is incubated with SACs for 12 hr, they will provide maximal stimulation and present the antigen in the context of their Ia molecules. UV irradiation of these SACs, prior to the 12-hr incubation with H-2Kk antigen, abrogates this stimulatory capacity. Macrophage-bound antigen is not sufficient for stimulation of a response; a second signal is required as well, that, in our system, is provided by phorbol myristic acetate. The SACs are involved in the activation of helper T cells; however, they are not required for presentation of antigen to the precytotoxic T-lymphocyte, which requires two signals for activation, one provided by antigen and the other by a T-cell-derived helper factor.

Lymphocyte recognition of H-2 antigen in liposomes

Liposomes containing purified H-2Kk will specifically stimulate generation of a secondary allogeneic cytolytic T lymphocyte response. Effective recognition was found to depend on the structure of the liposomes. Including detergent-insoluble plasma membrane matrix during formation resulted in liposomes having two- to fourfold more activity than those prepared using just lipid and H-2.