Lyt-23+ cyclophosphamide-sensitive T cells regulate the activity of an interleukin 2 inhibitor in vivo

Melatonin Increase as Predictor for Tumor Objective Response to Chemotherapy in Advanced Cancer Patients

Clinical studies have demonstrated an altered pineal function in cancer patients. Owing to the documented antineoplastic activity of the pineal gland, these anomalies could have a prognostic significance. This study was carried out to monitor changes in blood levels of melatonin, the most important pineal hormone, in relation to the clinical response to chemotherapy in human neoplasms. The study included 42 cancer patients of both sexes (breast cancer, 10; lung cancer, 13; colon cancer, 11; soft tissue sarcoma, 4; testicular cancer, 1; Hodgkin's disease, 1; peritoneal mesothelioma, 2). Melatonin serum levels were measured by radioimmunoassay before and 28 days after each cycle of chemotherapy. The results showed that, irrespectively of the type of tumor and chemotherapeutic regimen, 12/16 patients (75%) whose melatonin markedly enhanced after chemotherapy had an objective regression. In contrast, 2/26 patients only (8%) whose melatonin did not enhance after chemotherapy had a clinical response. The percentage of objective responses was statistically significantly higher in patients with a chemotherapy-induced melatonin increase than in those with no melatonin increase (p < 0.001). This study seems to demonstrate that melatonin determination can be used as a predictor of the objective response to chemotherapy in cancer patients. Moreover, it suggests that the antineoplastic effect of cytotoxic drugs may require participation of the pineal gland.

Treatment-induced antibodies to interleukin-2

Interleukin-2 (IL-2) is a 15 kDa glycoprotein with proven activity as an immune stimulant in the treatment of malignant disorders, congenital and acquired immune deficiencies, infectious disorders, and as an adjuvant to vaccines. Both natural and recombinant type IL-2 preparations have been applied in clinical treatment trials and have turned out to be immunogenic, although to a varying extent. Enzyme immunoassays and western blotting are standard procedures for the detection of IL-2-binding antibodies, whereas the neutralizing capacity of these antibodies is frequently demonstrated by inhibition of IL-2-dependent cell growth in vitro. The rate of treatment-induced IL-2 antibodies has varied from 0% to 100% in reported trials and frequently exceeded 50% in patients exposed to recombinant IL-2, whereas natural type IL-2 appeared to be little immunogenic. Duration of treatment, cumulative IL-2 dose, and route of IL-2 administration are likely to determine both the rate of seroconversion as well as composition and properties of the anti-IL-2 antibodies. Interleukin-2 antibodies are polyclonal in nature and predominantly composed of IgM and IgG types. Frequently they react with both recombinant and natural IL-2 types. As a rule, neutralizing IL-2 antibodies are detected in serum samples with high IL-2-binding titers and are recognized later than their non-neutralizing predecessors. Neutralization in vitro, however, does not predict neutralization in vivo, and there are very rare patients with documented, antibody-mediated loss of response to IL-2 treatment. More frequently, IL-2 antibodies will limit the expression of IL-2-dependent proteins in vivo, but the opposite has also been observed. Although the precise mechanism of antibody induction by IL-2 is unknown, immunogenicity of some drug formulations rather than polyclonal B-cell activation appears to play a critical role. Approaches aiming at limiting the immunogenicity of IL-2 preparations are discussed, and strategies how to recognize and circumvent antibody-mediated IL-2 resistance are presented.

Dual inhibitory and stimulatory activities in serum from SLE patients and lupus mice that regulate the proliferation of an IL-2-dependent T cell line

In serum and plasma from SLE patients, we have detected elevated levels of factors which regulate proliferative responses of CTLL cells to IL-2. Serum samples containing these factors have dose-dependent dual inhibitory and stimulatory activities on the proliferation of this IL-2-dependent T lymphocyte cell line. At high concentrations, the serum factors inhibit the proliferative responses of CTLL cells to IL-2. At low concentrations, they synergise with IL-2 stimulating the growth of cells. Similar inhibitory activity, but with lower titre, was also found to be elevated in sera of some MRL/lpr mice, an animal model of SLE. Functional characterisation of the serum factors shows that: (1) the inhibitory activity cannot be neutralised by exogenous IL-2; (2) the stimulatory activity is not due to the presence of serum IL-2 but synergy of the factor with IL-2; (3) the factors bind directly to CTLL cells but they do not bind to protein A; and (4) the serum factors are not dialysable but heat labile. The possible pathological implications of the serum factors, particularly for the defective T cell functions in lupus disease, are discussed.

Suppressin: an endogenous negative regulator of immune cell activation

We have recently identified a new suppressor molecule we named suppressin (SPN) that has all the characteristics of a global negative regulator of the immune system. SPN is a unique 63-kD monomeric polypeptide with a pI of 8.1 that is produced and secreted under basal conditions by murine splenocytes, human peripheral mononuclear cells, and hormone-secreting pituitary cells. The biological actions of SPN in vitro include the inhibition of mitogen-induced proliferation and immunoglobulin synthesis of lymphocytes and the suppression of interleukin-2-dependent CTLL-2 cell proliferation. In addition, SPN enhances natural killer cell activity by eliciting interferon-alpha and -beta synthesis and secretion. SPN effects are reversible, nontoxic, and require the continuous presence of exogenous SPN. T lymphocytes stimulated with concanavalin A or phytohemagglutinin are more sensitive to SPN (90% inhibition) than are lipopolysaccharide-stimulated B cells (60% inhibition). SPN arrests lymphocytes in the G0/G1 phase of the cell cycle after reduction of their RNA, protein and DNA synthesis, suggesting that SPN inhibits the processes required for G0 transition to G1. SPN is found intracellularly in all unstimulated lymphocyte subsets, monocytes, and in phytohemagglutinin-activated T lymphocytes immunopositive for the low affinity interleukin-2 receptor. These results suggest that SPN may be a major negative regulator of cell proliferation in the immune system. All SPN-producing cell types are also sensitive to SPN. Collectively, the results of these experiments provide the foundations for a model in which SPN regulates lymphocyte proliferation in an autocrine and/or paracrine manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Normal mouse serum-derived factor(s) which inhibits growth of the interleukin-2-dependent cell line CTLL

Evidence is presented for the existence of a serum factor(s) (SF), which inhibits the growth of both the interleukin-2 (IL-2)-dependent cell line CTLL and the 2-day generation of CTL cells. This activity is found in the serum of both nude and euthymic mice and its suppressive effect can be detected about 18 hours after addition to CTLL cultures. The inhibitory activity elutes from a Sepharose 6B gel after the gamma globulin fraction (100-150 kD), and is precipitated by ammonium sulfate at 60 w/v% saturation. IL-3-mediated bone marrow colony formation is not inhibited by SF. It also does not suppress the growth of a panel of different tumor cell lines. The spleen cell responsiveness to both Con A and LPS activation is greatly reduced in the presence of SF. However, binding of radiolabelled IL-2 to CTLL cells was not blocked by SF, although the activity was greatly reduced by absorption to these cells. Our data support the existence of factor(s) in sera that may have a regulatory role on IL-2-mediated functions.

The so-called interleukin-2 inhibitory activity of human serum is largely cytotoxic to mouse cells

No specific interleukin-2 (IL-2) inhibitor has ever been demonstrated in human, mouse, or any other animal serum. Native mouse serum contains activities which completely inhibit IL-2-dependent and IL-2-independent in vitro proliferation of cells of different animal species by a non-cytotoxic mechanism. The decisive inhibitory component of mouse serum has a molecular weight of about 80,000, is heat-labile and has not been found in other animal sera. Also, native human serum completely suppresses the proliferation of various mouse cell types, predominantly by a cytotoxic effect caused by natural IgM antibodies and complement. Heat-inactivated human serum is no longer cytotoxic to mouse cells, and inhibits the proliferation of mouse cells much less than native serum. There is thus no evidence for a specific IL-2 inhibitor in mouse, human or other serum.

Induction of LAK-like cells in the peritoneal cavity of mice by inactivated Candida albicans

We have investigated the effect of multiple administrations of inactivated Candida albicans (CA) cells on induction of non-MHC-restricted antitumor cytotoxic responses both in normal and congenitally athymic (nude) mice. Intraperitoneal inoculation of CD2F1 mice with five doses of 2 x 10(7) CA cells over a 2-week interval was associated with the induction of peritoneal exudate cells (PEC) that mediated natural killer cell activity. These cells, in contrast to those elicited by a single dose of CA, killed both NK-sensitive and NK-resistant tumor target cells in vitro. This broad-spectrum, antitumor cytotoxicity peaked 1 day after the last injection of CA, and decreased to control values within 6 (NK-resistant) or 14 (NK-sensitive target cells) days. Cytotoxicity could be recalled to a high level by a boosting injection of CA or a major mannoprotein-soluble antigen (MP) from the Candida cell wall, given 30 days after multiple CA treatment. Upon a 24-hr in vitro incubation, CA-induced peritoneal immunoeffectors lost their killing activity unless human recombinant interleukin-2 (rIL-2) was added to cultures. The non-MHC-restricted cytotoxic PEC activity induced by CA was mainly associated with nonadherent, nonphagocytic large granular lymphocytes (LGL) which exhibited the following phenotypes: (i) asialo GM1+, Lyt 2.2-, and partially Thy 1.2+ (effectors active against NK-sensitive targets) and (ii) asialo GM1+, Lyt 2.2-, and Thy 1.2+ (effectors active against NK-resistant targets). Nude mice also responded to multiple CA inoculations by displaying high cytotoxic activity against NK-sensitive targets and significant cytotoxicity against NK-resistant targets. This cytotoxicity could be recalled on Day +30, and the cytotoxic effectors involved were highly sensitive to anti-asialo GM1 plus complement treatment. Overall, the results add further experimental evidence to the wide range of immunomodulatory properties possessed by C. albicans, and demonstrate that the majority of antitumor cytotoxic activity induced by fungal cells was due to lymphokine-activated killer (LAK)-like effectors.

Immunological aspects of fungal pathogenesis

The incidence of infection with the pathogenic fungi continues to escalate, especially in the era of the acquired immune deficiency syndrome. To the clinician, this heterogeneous group of organisms poses both a diagnostic and a therapeutic challenge. Consequently, growing numbers of investigators are seeking to elucidate the pathogenetic mechanisms involved in disease caused by medically important fungi. In this review, many of the recent scientific advances that have been made in the immunological aspects of the pathogenesis of fungal infections are presented. The topics covered include 1) the receptors for fungi on the surface of professional phagocytes; 2) the mechanisms for killing and growth inhibition of fungi by phagocytes; 3) the means by which fungi evade host defenses; 4) the role of humoral immunity in fungal infection; 5) immunoregulation in fungal infections; and 6) the influence of cytokines on host defenses against pathogenic fungi.

Combination chemo-immunotherapy: kinetics of in vivo and in vitro generation of natural killer cells and lymphokine-activated killer cells in the rat

Rats received a single high dose of cyclophosphamide (Cy) (150 mg/kg), followed 48 h later (on day 0) by immunization with a T cell-dependent soluble antigen, ovalbumin in Freund's complete adjuvant (FCA). The effect of this treatment on lymphoid cell subpopulations in the spleen, natural killer (NK) cell and interleukin-2 (IL-2) induced lymphokine-activated killer (LAK) cell activity was examined. Cy (with and without ovalbumin) caused a large relative increase (by day 14) in splenic OX8+, OX19- cells with NK morphology. A marked relative increase in fresh NK cell activity was noted after Cy + ovalbumin, but not consistently after Cy alone. Elevated NK activity was Cy dose- and time-dependent, was evident within 7 days post Cy/ovalbumin and persisted for at least 28 days. Pooled splenic mononuclear cells (MNC), obtained 14 days after Cy/ovalbumin, lost all cytolytic activity against YAC-1 cells when cultured in the absence of human recombinant IL-2 (rIL-2). In contrast, similarly maintained cells from normal rats displayed NK activity higher than normal 'fresh' levels. Upon culture in medium containing 500 U/ml rIL-2, however, 'augmented' NK activity was equivalent, on a per-cell basis, in both normal and Cy/ovalbumin-pretreated groups. LAK activity generated in vitro (i.e. against NK-resistant target cells) was significantly lower in the latter group, and the overall yield of cells was reduced. By day 21 after Cy/ovalbumin, augmented NK activity was significantly greater than controls, on a per-cell and total culture yield basis. Moreover, LAK activity was now similar between groups. It is concluded that the chemotherapy/immunization protocol which we have used can greatly enhance NK activity in vivo and that these cells are responsive to induction of LAK activity by IL-2 in vitro.

Suppression of interleukin-2 mediated T-lymphocyte blastogenesis by bovine uterine secretions

Uterine luminal protein (ULP) secretions collected on day 17 of bovine pregnancy contain high (greater than or equal to 248 kDa)- and low (7, 21.0, and greater than or equal to 72 kDa)-molecular weight (Mr) components that suppressed incorporation of thymidine into both phytohemagglutinin (PHA)-stimulated and interleukin-2 (IL-2)-stimulated bovine lymphocytes. The pattern of suppressor activity for ULP was similar for both PHA and IL-2 cultures. For IL-2-treated lymphocytes (2 X 10(4)/culture well), mean percentage of control (no test protein) values for 8 and 32 micrograms/ml of high Mr ULP were 94.6% and 4.5%, respectively; whereas, mean values for 8 and 64 micrograms/ml of combined low Mr ULP components were 51.2% and 5.5%, respectively. The data indicate that specific bovine ULP components may locally affect T-lymphocyte function by altering some facet of the IL-2 activation system.

Interleukin-2-dependent control of disease development in spontaneously diabetic BB rats

Long-term treatment with recombinant interleukin-2 (IL-2) of diabetes-prone BB rats had contrasting effects in two different BB rat sublines. Diabetes development was enhanced in the subline with a low intrinsic diabetes risk and suppressed in the subline with a high diabetes risk. IL-2 treatment started between 35 and 42 days of age and lasted for 3 months. In subline 1, diabetes incidence increased from 23% to 53% (P less than 0.01), in subline 2 it decreased from 73% to 32% (P less than 0.01). The two sublines differed in serum levels of factors controlling IL-2 synthesis and activity. Mean IL-2 inhibitory activity was higher in subline 2 (between 140% and 290% of levels in subline 1, P less than 0.01). Conversely, mean concentrations of thymosin alpha 1 and beta 4 were higher in subline 1 (between 140% and 200% of levels in subline 2, P less than 0.01). Thus the two sublines differ in their response to exogenous IL-2 and also in serum levels of mediators affecting availability of IL-2. We conclude that an internal network of hormonal factors, including IL-2, contributes to the control of diabetes development in the BB rat.

Antibodies to interleukin 2 in sera of autoimmune-prone mice

Autoimmune-prone mice spontaneously develop the disease characterized by autoantibodies to a wide variety of antigens. In the present study, we have demonstrated that IgG antibodies to interleukin 2 (IL-2) are to be found in serum of autoimmune mice in association with ageing. These antibodies can neutralize the biological activity of IL-2 and thus play an important role in the etiopathogenesis of autoimmune disease.

Human immunosuppressive factors produced by T cell hybridoma

A Human OKT8-positive T cell hybridoma was established by using concanavalin A (ConA)-activated peripheral blood mononuclear cells (PBMC) fused with CEM-AGR cells. A culture supernatant of the established T cell hybridoma HI4.2D6 inhibited the mitogen induced proliferation of peripheral blood mononuclear cells (PBMC). It inhibited IL-1-, IL-2, or IL-3-dependent proliferation of each factor-dependent mouse cell lines. While the inhibitory activity of IL-1-induced proliferation was stable, that of IL-2- and IL-3-induced proliferation was abrogated within a week at 4 degrees C. Inhibition of IL-2-dependent growth was also observed using human IL-2-dependent cells, but the growth of other factor-independent human hematopoietic cell lines was not affected at all. By gel filtration, the activity inhibiting IL-2- or IL-3-dependent proliferation was found in the fractions with approximate molecular weight of 18,000 and 100,000.

A fluorescence sandwich ELISA for detecting soluble and cell-associated human interleukin-2

A fluorescence sandwich ELISA was developed for the quantitation of human interleukin-2 (IL-2) using a combination of two anti-human IL-2 antibodies, L61 and biotinylated anti-IL-2 rabbit IgG. The minimum level of IL-2 detectable by this ELISA was 0.3 pg/ml, indicating that this method is about 100 times more sensitive than the usual colorimetric human IL-2 ELISA. The ELISA specifically detected human IL-2 in cell culture supernatants and serum, and also in extracts from mitogen-stimulated peripheral blood mononuclear cells. All of the IL-2 species detected in the supernatants, sera and cell lysates were shown to have a molecular weight of 15,000, as estimated by size exclusion high performance liquid chromatography.

The immune function of the endometrium

The endometrial mucosa is unique amongst mucosal sites in that it must mount an immune response against micro-organisms and resist tumour growth whilst tolerating sperm and the allogeneic fetus. Bacterial and viral infection in the uterus leads to local endometrial mucosal immune responses evidenced by the secretion of secretory component (SC), secretory IgA (sIgA) and IgG. The secretion of these molecules is under hormonal control. Trafficking of locally sensitized lymphocytes to other mucosae does not appear to occur, whereas priming at other mucosal surfaces leads to memory responses to antigen in the uterus. Proclivity to local immune function is related to sparse lymphatic supply to the endometrium together with a local distribution of antigen-presenting dendritic cells. During pregnancy, particularly in the region of the decidua and embryo, the number of Ia+ cells and the lymphatic supply become diminished. The antigenic status of sperm may lead to certain types of maternal sensitization. However, immunosuppressive factors in seminal plasma protect the sperm on its passage up the female genital tract and diminish subsequent immunogenicity. On fertilization of the oocyte, an allogenic fetus develops, that potentially could stimulate production of maternal immune effectors. Endometrial cells of various types (macrophage, decidual, NK, T cells) interact via soluble factors leading to a local immunoprotection of the fetus. Similar factors appear to operate in resisting tumour growth in the uterus.

Evidence of a plasma-mediated "window" of immunodeficiency in rats following trauma

The etiology of immunodeficiency following trauma was investigated. Plasma collected from Fischer rats 1-8 hr following a 40% surface area thermal injury (TI) displays immunosuppressive activity (ISA). Peak ISA (4 hr) exceeded 90% inhibition of Con A3-induced proliferation of normal spleen cells. Splenic macrophage IL-1 secretion and NK activity are also inhibited by 4-hr TI plasma. Most importantly, these same cellular immune functions decline in rats by 4 hr following TI. After a further decline by 16 hr (IL-1 = 19.8% and NK activity = 40% of normal), these cellular immune functions rebound toward normal values by 2 days following TI. Thus, ISA in plasma is both temporally and functionally linked to the cellular immune defects observed. Sham-treatment rats display a similar, although less marked, pattern of plasma-linked transient cellular immune defects indicating a role for stress in these responses. ISA is abolished by mild heat (56 degrees C for 30 min) and wholly contained in the greater than 10-kD fraction of plasma. Together, these results provide evidence that previously unrecognized molecules in plasma induce a "window" of immunodeficiency early following trauma.

Suppression of interleukin 2 production by sera obtained from hypersensitivity granuloma-bearing mice with defective T cell-mediated immune responses

Hypersensitivity pulmonary granulomas were able to induce by the intratracheal injection of antigen-conjugated Sepharose 4B beads into immunized mice. The mice with hypersensitivity granulomas showed a lack of T cell-mediated immune responses to antigens both in vivo (delayed type footpad reaction) and in vitro (lymph node cell proliferation) in association with impaired interleukin 2 (IL 2) production by suppressor cells in lymph nodes. However, no immunosuppressive factors were detected in the granuloma lesions. In the present study, we describe that the sera obtained from these mice contain suppressive factor(s) capable of inhibiting IL 2 production by immune lymph node cells. The appearance of serum suppressor factor(s) is correlated well with inhibition of delayed hypersensitivity in such mice. Partial characterization of suppressor factor(s) showed it is absorbed by T cells and may be proteins. The approximate molecular weight of the factor ranged from 12 to 67 kd. These results suggest that the suppressive mechanisms such as the suppressor cells and serum inhibitory factor(s) may be responsible for the impaired IL 2 production and, therefore, for the lack of both in vivo and in vitro expressions of T cell-mediated immune responses to antigens in mice with hypersensitivity granulomas.

The use of mouse serum and the presence of non-adherent cells for the culture of mouse macrophages

Mouse serum (MS) was investigated as an alternative to fetal calf serum (FCS) as a medium supplement for the culture of murine macrophages. Peritoneal macrophages were successfully cultured in medium supplemented with 1-20% MS and were able to produce superoxide anions in response to stimulation with phorbol myristate acetate (PMA) and to phagocytose antibody-coated erythrocytes effectively. Macrophages cultured in the presence of 5% or 20% FCS showed a generally augmented response to PMA, raising the possibility that they had been 'primed' by constituents or contaminants of FCS. Lipopolysaccharide-elicited macrophages initially showed vigorous in vitro responses to PMA which decreased with increasing culture time in MS-supplemented medium. This 'de-differentiation' of elicited macrophages could be due to the absence of LPS contamination and foreign protein when autologous serum is used as a medium supplement. In all cultures the presence of non-adherent cells for the first 24 h increased the number and superoxide response of adherent cells. MS is a convenient, reliable and inexpensive alternative to FCS as a medium supplement for murine macrophage cultures.

Human hybridoma suppressor factor acts selectively on CD4+ cells

A human thymus cell hybridoma secretes an immunosuppressive lymphokine, referred to as hybridoma suppressor factor (HSF). This factor suppresses polyclonal immunoglobulin (Ig) production as well as Interleukin-2 (IL-2) production in pokeweed mitogen (PWM)-stimulated peripheral blood mononuclear cells (PBMC). Similar suppression of Ig and IL-2 production was observed in reconstituted cultures of CD4+ cells and non-T cells. Here we analysed, further, the mechanism of HSF-mediated suppression of Ig and IL-2 production. We demonstrated that HSF inhibited PWM-induced IL-2 production by CD4+ cells but not by CD8+ cells and its suppressive activity on Ig production was totally abrogated by preabsorption with CD4+ cells, but not by CD8+ cells. These results indicate a subset specific action of HSF.

Con A-stimulated thymocytes produce interleukin 2 after removal of Lyt-1 positive cells

Mouse lymphocytes produce several lymphokines, including interleukin 2 (IL-2) and colony-stimulating factors (CSFs) following stimulation with T-cell mitogens. However, very little IL-2 is produced by thymocytes upon concanavalin A (Con A) stimulation. Strong selective inhibition of IL-2 production was observed when fresh spleen cells were mixed with Con A-activated thymocytes. Sorting of populations on the basis of antigenic phenotype showed that the cell mediating the blockage in IL-2 secretion is a large T cell expressing markers for both Lyt-1 and Lyt-2. This specific inhibition of IL-2 accumulation was not mediated by a soluble product, or by absorption on expressed IL-2 receptors on the activated thymocytes. Removal of the Lyt-1 positive cells from a thymocyte population renders it capable to produce IL-2 upon Con A stimulation, indicating a functional role of these cells.

The autonomy of CD8+ T cells in vitro and in vivo

Experiments have been carried out in vitro and in vivo to determine to what extent CD8+ T cells in the rat can function independently of any helper activity from CD4+ cells. We have identified the culture conditions required for the autonomous proliferation of CD8+ T cells in the rat mixed leucocyte culture (MLC) and in particular have studied both the kinetics of the response and the effect of replacing the homologous serum, used in our previous MLC experiments, with fetal calf serum (FCS). The results obtained using FCS show that, early in the MLC, CD8+ T-cells proliferate at a comparable rate to the CD4+ subset but that, within 48-72 hr, the proliferation rate of the CD8+ cells ceases to increase with time. In contrast, the proliferation of the CD4+ T cells appears to be limited only by the exhaustion of the culture medium. The results also show that the proliferative responses of both CD4+ and CD8+ T cells are inhibited in homologous serum but that it is the CD8+ subset that is more affected. When CD8+ T cells, in homologous serum, are co-cultured with irradiated CD4+ T cells the proliferative activity is increased, indicating that the helper activity of the CD4+ T cells can over-ride the inhibitory effect of the serum. In vivo we have compared the abilities of injected CD4+ and CD8+ T cells to mediate rejection of skin allografts on nude rats. Grafts were rejected more rapidly on recipients of low doses of CD4+ T cells than on rats given 200 times as many CD8+ T cells. Thoracic duct lymphocytes (TDL) obtained 5 weeks after CD8+ T-cell injection always contained a population of CD4+ T cells, even when the injected CD8+ T-cell inoculum contained less than 0.1% CD4+ cells as contaminants. Evidence was obtained that these CD4+ T cells found in TDL displayed alloreactivity in MLC. Further, the intentional injection of very low doses of CD4+ cells led, after 5 weeks, to frequencies of CD4+ T cells, in thoracic duct lymph, equal to that obtained by the injection of 200 times as many cells of the same phenotype. It appears that, in T-cell-deficient rats, CD4+ cells can expand over 2000 times in a few weeks. Such expansion may explain the relatively slow rejection of skin allografts observed in these experiments when nude rats were injected with putatively pure populations of CD8+ T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Down-regulation of cytotoxic T lymphocyte generation by two distinct suppressor-cell systems

Two distinct suppressor systems have been described that are capable of down-regulating in vivo generation of cytotoxic T cells directed toward haptenaltered self-antigens. One system, induced by hapten, involves three T cells that others have shown to function sequentially to suppress DTH. The initiator of this cascade is a T cell that is readily induced in spleens of mice injected intravenously with syngenic membrane-coupled hapten. This Ts, when triggered by the same syngeneic membrane-coupled hapten that induced it, elaborates a factor. The other two Ts arise in lymph nodes and spleens of mice painted epidermally with hapten. One of the two Ts in this set is readily armed by the factor of the first Ts. The factor confers its specificity and genetic restriction upon the accepting Ts. The latter, when properly triggered, makes a factor that is taken up by its companion Ts, which actually suppresses by way of a nonspecific factor. Whereas this Ts cascade is operative at the efferent limb of DTH, it mediates suppression only at the afferent phase of the CTL response. A distinctly different suppressor system is induced by minor locus (Mls) antigen. When Mlsd lymphoid cells are injected intravenously into Mlsc-possessing mice, an Lyt-1+ T-suppressor cell is generated that can be found in the spleen as well as among peritoneal exudate cells. This Ts interacts with macrophages to accomplish nonspecific suppression of the CTL response that is detectable both in vivo as well as in vitro. A Ts soluble product has been found to be effective to suppress CTL generation in vitro only when macrophages are present in culture. The macrophage that accomplishes suppression is I-A-. Although the afferent limb of the CTL response is down-regulated by this suppressor system, our in vitro culturing system is so structured as to make the helper T cell inactive. Thus, the mechanism of suppression must be oriented to the other early participants in the response, namely, precursor CTL, helper and differentiation factors, and/or the antigen-presenting cell.

Characterization of lymphocytes that suppress IL-2 production in systemic lupus erythematosus

IL-2 production by peripheral blood mononuclear cells (PBM) is decreased in patients with systemic lupus erythematosus (SLE). This defect can be reversed by the removal of CD8+ lymphocytes. The purpose of these studies was to determine whether the CD8+ IL-2 suppressor cells comprise a specific subset or whether all CD8+ cells have this activity. Lymphocyte subsets were identified and separated by two-colour flow cytometry prior to a 48 h mitogen stimulation. The CD8+ cells that suppressed IL-2 production co-expressed HLA DR and were radiosensitive. Other markers co-expressed by CD8+ cells which are found on suppressor cells such as Leu 15 (CD11), Leu 11 (CD16), and Leu 7 were also found on the CD8+ IL-2 suppressor cell population in SLE. In healthy subjects, removal of CD16+, but not of CD8+ cells markedly elevated the production of IL-2. The CD8- CD16+ non-T cell subset suppressed IL-2 production by normal and SLE PBM in autologous and allogeneic combinations. This subset may be a human equivalent of the murine natural suppressor cells. These results demonstrate that the cells that suppress IL-2 production in SLE are heterogeneous, and suggest that they belong to more than one lineage.

Decreased activity of interleukin-2 inhibitor in plasma of patients with systemic lupus erythematosus

Low levels of plasma interleukin-2 inhibitory activity were found in patients with systemic lupus erythematosus (SLE) compared to normal individuals. The depression of the inhibitory activity was significant in patients with severe and moderate SLE while only a slight decrease was observed in the mild form of the disease.

Serum inhibitors of interleukin-2

Interleukin-2 (IL-2) is an important modulator of cell-mediated immunity. Its activity is suppressed by various serum inhibitors generated under normal and pathological conditions. It is believed that an inhibitor which occurs in normal serum is a T-cell derived heat labile protein (or protein-glycolipid complex), and it acts in a homeostatic mechanism to restrict IL-2 action to the vicinity of the activated T cells. Changes in inhibitory activity have been found in various physiological and pathological states, e.g. during ontogeny, in systemic lupus erythematosus, in rheumatoid arthritis, and with some systemic infections. There are also suggestions that some tumor cells generate IL-2 inhibitors which diminish killer cell activity against the tumor. It is possible that a better understanding of IL-2 inhibitors would help elucidate some pathological mechanisms connected with disturbed cellular immune responses.

L3T4+ T-cell-independent reactivity of Lyt2+ T cells in vivo

The aim of this study was to analyze in vivo the L3T4+ T-cell-subset-independent reactivity of Lyt2+ T cells toward transplantation alloantigens. To this end, we depleted normal mice of L3T4+ T cells by injection of monoclonal antibodies to the L3T4 antigen. This procedure not only led phenotypically to a disappearance of L3T4+ T cells, but also effectively abolished reactivity toward class II MHC antigens in vitro and in vivo. However, L3T4+ T-cell-depleted mice still reacted to class I MHC alloantigens in vivo: after immunization with class I MHC alloantigens Il-2 receptor-bearing T cells appeared in the draining lymph nodes, and developed antigen-specific cytolytic activity. Moreover, upon in vivo priming the frequencies of class I MHC-specific precursors of Il-2-producing and cytolytic Lyt2+ T lymphocytes increased up to 20-fold. L3T4+ T-cell-depleted mice rejected class I MHC-bearing skin grafts promptly. We conclude that not only in vitro but also in vivo Lyt2+ T cells remain reactive toward class I MHC antigens in the absence of L3T4+ T helper cells.

Suppressive and enhancing effect of T-2 toxin on murine lymphocyte activation and interleukin 2 production

T-2 toxin, a fungal metabolite shown previously to exert potent immunosuppressive effects, was examined for its effects on activation and interleukin 2 (IL 2) production by murine and rat splenocytes. Splenocytes (1 X 10(6) cells/well) were incubated with 1 microgram Concanavalin A (Con A) for 48 h at which time cellular protein and DNA synthesis by these cells were ascertained using radiolabeled precursors. IL 2 synthesis was determined from the cell supernatant using the IL 2-requiring cell line CTLL. Spleen cells from mice treated for 4 consecutive days with 2 mg/kg toxin exhibited a 50% reduction in in vitro Con A activation but the supernatant IL 2 levels from these cells was 4-fold higher than cells from control mice. In vitro exposure of Con A-activated normal spleen cells to various toxin doses for 48 h resulted in diminished protein and DNA synthesis at 0.4 ng toxin with maximum inhibition at 1 ng (50% inhibition (TCID50) = 0.5 ng). Enhanced synthesis of both products was observed at lower toxin concentrations. IL 2 production by these cells followed a similar toxin dose response. Rat splenocytes were slightly more resistant and CTLL cells were slightly more sensitive to T-2 toxin than mouse splenocytes. These results indicate the variable effects a cytotoxic agent can have on lymphoid cells and that dosage is an important parameter for these effects.

Inhibition of human lymphocyte proliferative response by serum from Plasmodium falciparum infected patients

Malaria infection has been shown to induce alterations in immune reactivity. This report describes the effect of serum obtained from Plasmodium falciparum infected patients on in vitro proliferation of human blood mononuclear cells (BMNC) isolated from healthy individuals. Serum obtained before initiation of treatment suppressed the in vitro lymphocyte proliferative response to both Plasmodium-derived antigens and an unrelated antigen (PPD-tuberculin). The suppressive effect was lost if the serum was incubated at 56 degrees C for 30 min, and the effect was not HLA-restricted since the inhibition was seen on both autologous and heterologous BMNC. The degree of suppression was not correlated to the duration of the disease, the degree of parasitemia, or the use of chemoprophylaxis. Sera from 7 patients before and from 3 patients 30 days after initiation of treatment were pooled and fractionated. It was found that the strongest suppressive activity was in the serum fraction containing molecules from 30-100 kD.

Apparent interleukin 2 (IL-2) inhibitory activity of human serum is due to rapid killing of IL-2-dependent mouse cells

A number of investigators have reported that human serum inhibits the proliferation of IL-2-dependent mouse cells in IL-2 bioassays, but the mechanism of inhibition has not been carefully examined. We noticed that IL-2-dependent mouse cells (CTLL-2) are killed within 30 min in the presence of a 1/10 dilution of human serum. However, CTLL-2 cells totally deprived of IL-2 did not begin to die until at least 6 h in culture. Thus, even complete inhibition of IL-2 by human serum could not account for the rapid cytotoxicity caused by human serum. Since humans have 'natural' antibodies which react with mouse cells, it seemed possible that the cytotoxicity was due to antibody/complement-mediated cell lysis. This was supported by the observation that EDTA (at a concentration sufficient to inhibit complement) protected CTLL-2 cells from the cytotoxic effects of human sera from four normal donors. In addition, preincubation of CTLL-2 cells with heat-inactivated human sera at 4 degrees C rendered them much more susceptible to lysis with rabbit complement than cells which were preincubated with complete culture medium. The cytotoxicity of human serum is not limited to IL-2-dependent mouse cells but was also observed with EL4 and Ag8.653 cells as well as normal splenocytes. The cytotoxic effect of human serum was lost upon removal of IgM, but not upon removal of IgG. These results strongly suggest that the inhibition of proliferation of IL-2-dependent mouse cells by human serum is due to antibody/complement-mediated lysis of those cells. In addition, non-heat-inactivated human serum did not inhibit the IL-2-mediated proliferation of human PHA blasts, indicating that there is no inherent inhibitory activity in human serum apart from the cytotoxic effect on xenogeneic cells. Thus the reported IL-2 inhibitory activity of whole human serum is probably not biologically relevant.

Effects of serum immunosuppressive factors on antitumor cytotoxicity of interleukin 2-induced lymphocytes

The cytotoxic ability of interleukin 2 (IL2)-induced T cells and the effect on their cytotoxicity of serum suppressive factors obtained from cancer patients were examined. Peripheral blood mononuclear cells (PBL) of healthy adults were IL2-cultured for 72 h either together with a gastric carcinoma cell line MKN-28 or with phytohemagglutinin, then IL2-cultured for another 11 days. Cytotoxicity of the MKN-28 precultured lymphocytes against MKN-28 was particularly increased. Presence during preculture or during cytotoxicity assay of sera from gastric cancer patients having the same histological type as MKN-28 suppressed the cytotoxicity. However, the serum suppressive effect on cytotoxicity of the IL2-cultured lymphocytes was far milder than that on PBL cytotoxicity.

Alloimmune cells consume interleukin-2 and competitively inhibit the anti-tumour effects of interleukin-2

Adoptive immunotherapy with lymphokine activated killer (LAK) cells and recombinant interleukin-2 (IL-2) is successful in a variety of tumour models in both the normal and the immunocompromised mouse. We investigated the effects of an immune response to an allogeneic challenge on the metabolism of IL-2. Serum IL-2 levels at different time points after the administration of 20,000 units of IL-2 intraperitoneally were 2-4 fold higher in normal mice than in recently alloimmunized mice. In an intraperitoneal tumour model the alloimmunization of mice with allogeneic P815 tumour cells or splenocytes IP prior to the intraperitoneal inoculation of syngeneic tumour significantly diminished the anti-tumour effects of IL-2 and LAK cell immunotherapy in 7 consecutive experiments. High doses of IL-2 or pretreatment with cyclophosphamide restored the efficacy of IL-2 and LAK cell immunotherapy. From these results we hypothesize that T cells, activated by the allogeneic challenge, consume IL-2 and thus inhibit the effects of IL-2 and LAK cell treatment by competitive inhibition. LAK cell activity with reduced levels of IL-2 cannot be maintained and anti-tumour effects are lost. High doses of IL-2 were shown to overcome the competition for IL-2. Alternatively activated T-cells could be eliminated by pretreatment with cyclophosphamide and anti-tumour effects restored. These results are important in that they provide an alternative explanation as to the mechanism of non-specific cell mediated suppression and may in part explain the failure of some cancer patients to respond to treatment with IL-2 plus LAK immunotherapy.

Lymphokine-activated killer cell and interleukin-2 inhibitors: their role in adoptive immunotherapy

Interleukin-2 (IL-2) and the adoptive transfer of lymphokine-activated killer (LAK) cells have been used to reduce tumor mass in intraperitoneal, pulmonary, and hepatic models. Unfortunately, repeated cycles of IL-2 plus LAK cells have not been demonstrated to exert additive antitumor effects. We investigated the responses that repeated challenge with LAK cells and IL-2 provoked in normal BL/6 mice. Six immunizations of LAK cells generated in media containing fetal calf serum abrogated the ability of mice to respond to IL-2 plus LAK immunotherapy in a peritoneal carcinomatosis model. Serum from these treated mice would cause lysis of LAK cells or cultured lymphocytes in the presence of complement. LAK cells generated in the presence of normal mouse serum were not lysed. Similarly, the antitumor effects of IL-2 plus LAK immunotherapy were abrogated in mice pretreated with six courses of IL-2. We found that LAK cells cytolysis could not be generated if serum from IL-2-pretreated mice was present in vitro with splenocytes and IL-2. These data suggest that antibody against absorbed antigens on LAK cells and serum inhibitors of IL-2 are generated following repeated challenge. These observations may be important in interpreting IL-2 plus LAK immunotherapy studies in murine models and may modify our attempts to treat cancer patients.

Serum-mediated suppression of nonspecific B-cell activation. III. Selective inhibition of the polyclonal B-cell response by normal mouse serum

Normal, nonimmune adult serum is known to inhibit in vitro immune responses when present in sufficient amounts. The significance of inhibition of the immune response by serum, however, is not known. Previous work suggested that normal mouse plasma or serum (NMS) was selectively more inhibitory to nonantigen-specific (e.g., polyclonal) as compared to antigen-specific responses. This led to the hypothesis that constituents of serum (or plasma) may serve naturally to minimize the polyclonal type of antibody response, preserving immune specificity. The present study further examined the effect of NMS on polyclonal versus antigen-specific antibody responses. Under the in vitro assay conditions used, 0.5% NMS supported bacterial endotoxin (ET)-induced mitogenic and polyclonal B lymphocyte responses, antigen (SRBC, TNP-KLH)-specific antibody (IgM, IgG) responses, and antigen-induced or -specific T-lymphocyte proliferative responses, while 5% NMS inhibited all of these responses. However, antigen-specific T-lymphocyte responses could be restored by a 10-fold increase in the antigen concentration and antigen-specific antibody responses could be restored by the addition of ET (10 micrograms/ml) as adjuvant. On the other hand, the mitogenic response to ET remained suppressed regardless of ET concentration. Thus, despite significant reduction of the mitogenic and polyclonal properties of ET in 5% NMS (greater than 70% suppression), sufficient antigenic stimuli permitted optimal specific T- and B-cell responses. Many naturally occurring antigens, e.g., bacterial, fungal, and viral, have inherent B-cell mitogenic and polyclonal activity in addition to adjuvanticity and the presence of the serum inhibitory factor may serve to minimize their indiscriminate polyclonal stimulation of antibody.

Suppression of interleukin 2 activity by natural products: effects of serum lipoproteins

The results presented here demonstrate that mouse serum lipoproteins inhibit Interleukin 2 (IL2)-mediated proliferation of CTLL-2 cells. Lipoproteins account for a variable portion (29-83%) of the total inhibitory activity of whole serum and are not specific inhibitors of IL2-mediated cell proliferation, as evidenced by their inhibitory activity for non-IL2-dependent MPC 11 cells. Lipoproteins did not accelerate the death of CTLL-2 cells deprived of IL2, indicating that their inhibition of proliferation is not due to toxic effects. Finally, the inhibitory activity of serum and isolated lipoproteins was increased when the donor mice were maintained on a diet high in polyunsaturated fats for 16 days prior to bleeding. These findings provide a basis for future investigations of the relationship between dietary fats, lipoprotein quantity and composition, and alteration of immune responses.

A syngeneic splenic cell antigen induces a suppressor T cell in lymph nodes that controls cytotoxic T-cell and primary antibody responses

The nonspecific suppression of immunological responses that is generated within host popliteal lymph nodes upon exposure to syngeneic normal spleen cells has been examined. The suppression, which had previously been described as being capable of preventing initiation of cytotoxic T lymphocytes (CTLs) to hapten-altered self antigens, arises within 3 to 7 days after injecting the spleen cells. Suppression was shown to be attributable to an induced T cell that was functional when transferred intravenously. Although the cell surface marker(s) on both splenic B and T cells that stimulates appearance of Ts has not yet been identified, the cells possessing the marker were not required to be viable to cause the induction. We have shown here that the Ts is fully functional when it is put in the antigenic site used for CTL immunization. The induced Ts has been identified as bearing the Lyt 2.1 cell surface marker. Furthermore, it has been shown to be insensitive to cyclophosphamide (CY), thus differentiating it from the naturally occurring Ts cell (TS0) that is known to be CY sensitive. In addition to preventing induction of CTLs toward hapten-altered self antigens, exposing popliteal lymph nodes to syngeneic spleen cells induced Ts capable of suppressing the primary IgM antibody response to sheep red blood cells. The Ts cells that suppressed the primary antibody response possessed the same Lyt cell surface markers and CY insensitivity as the Ts that mediated suppression of the CTL response. Thus, evidence that two dissimilar immunological reactions may be down-regulated by the same suppressor mechanism has been provided. Results of a kinetic study showed that the Ts prevented development of both the humoral and the cell-mediated immune responses by affecting their inductive phases. Possible targets for suppression that more than likely would have to be common to the two widely different immune responses have been indicated.

The suppressor T cell induced by syngeneic splenic cell antigen down-regulates hapten-specific cytotoxic T cells by elaborating a factor inhibitory for IL2-dependent cell replication

An in vitro study has been made of the mechanism by which a suppressor T cell, that is induced in lymph nodes by a syngeneic splenic cell antigen, prevents generation of cytotoxic T cells specific for hapten-altered self antigens. When popliteal lymph node cells exposed in vivo to syngeneic splenic cells were immunized in vitro with heat-treated syngeneic TNP-coupled thymocytes and excess helper factors, the Ts remained inactive. In this condition the exposed popliteal lymph node cells routinely demonstrated approximately twice the CTL response developed by lymph node cells from normal mice. Nevertheless, when triggered in vitro by splenic antigen on either X-irradiated B or T cells, the exposed but not the normal lymph node cells exhibited reduced hapten-altered self-specific CTL responses. Furthermore, T cells within spleen cell-exposed popliteal lymph node cell populations when reexposed to splenic T cells made a factor that was found to be suppressive of CTL generation by normal lymph node cells in vitro. The nondialyzable T-cell suppressor factor (TsF) did not appear to act on lymph node precursor CTLs, nor on helper T cells but instead acted at the level of utilization of helper factors in the development of CTLs. In an examination of the effect of TsF on cellular replication, TsF was found to be nontoxic for CTLL-20, an IL-2-dependent T cell, and it did not hinder the uptake of IL-2 by receptor blockade of this cell. Nevertheless, the replication of CTLL-20 that is IL-2 driven was diminished in the presence of TsF. Similarly, TsF was found to be inhibitory for T-cell proliferation stimulated by mitogen but had no effect on a B myeloma cell proliferative response. Thus, TsF appears to act as an inhibitor of a T cell's capability to replicate despite the presence of the stimulus for replication, namely, IL-2.

Deficiency of interleukin 2 inhibitor activity in serum from autoimmune-prone mice

To study the mechanisms that regulate the activity of interleukin 2 (IL 2) and possibly limit its activity, we have examined normal mouse serum for their ability to inhibit IL 2-mediated proliferation of a cloned IL 2-dependent cytotoxic T lymphocyte line (CTLL). Normal mouse serum contains a factor capable of inhibiting IL 2 dependent proliferation of CTLL cells. This factor is absorbed with IL 2-dependent cells, but not with IL 2 molecules. Decreased activity of the inhibitor is observed in serum from autoimmune-prone mice such as NZB and NZBWF 1 hybrid mice. The results suggest that the serum IL 2 inhibitor may play an important role in the in vivo regulatory mechanism of IL 2 activity and that lack of the inhibitor may be associated with aberrant immune functions.

Immunosuppressor factor(s) produced by decidua-associated suppressor cells: a proposed mechanism for fetal allograft survival

Mechanisms that explain failure of rejection of the antigenic fetus by the mother appear to lie at the fetomaternal interface. Successful pregnancies have been correlated with the presence of decidua-associated suppressor cells. Supernatants from these cells were tested for their ability to suppress the proliferation of interleukin 2-dependent cells and were also subjected to high-performance liquid chromatography. Decidual supernatant was found to have peak suppressive activity at two molecular weights (43,000 and 21,000 daltons). The activity of decidual supernatant was directed specifically at interleukin 2-dependent cells and interfered with interleukin 2 action. The importance of this mechanism in graft rejection is well known. Decidual supernatant may thus prevent fetal allograft rejection by preventing the maternal cytotoxic effectors from receiving the interleukin 2-dependent help that they need to proliferate and remain actively cytolytic.

Is there an interleukin 2 inhibitor in human serum?

Normal mouse serum has been shown to contain an inhibitor of interleukin 2 (IL-2). Here we report that a molecule with similar activity cannot be found in normal human serum (NHS). Although NHS inhibited the IL-2-dependent proliferation of mouse CTLL cells, as expected of an IL-2 inhibitor, it also had inhibitory activity on IL-3-dependent cells and was cytolytic to IL-2-independent mouse cells as measured by a 51Cr release assay, indicating a nonspecific effect. In addition, NHS had no effect on the IL-2-dependent proliferation of human peripheral blood T-cell blasts. Fractionation of NHS by size exclusion HPLC failed to separate cytolytic activity from any putative true IL-2 inhibitor activity. The cytolytic component was not related to immunoglobulin since it had a molecular weight of 50,000 to 60,000 and was not bound by protein-A-Sepharose. However, its molecular weight, heat lability, and trypsin sensitivity suggest it to be a protein.

IgG from Epstein-Barr virus infectious mononucleosis patients inhibits interleukin-2 production

Patients with Epstein-Barr virus (EBV)-associated dissorders usually demonstrate evidence of immunosupression during active disease. Sera of some patients with EBV-induced infectious mononucleosis (IM), contain an IgG-blocking factor (IM-IgG) which inhibits in vitro cell-mediated immune responses and which we postulate plays an important role in viral immunosuppression. We had shown earlier that Isoprinosine (an immunostimulator) has a counterinhibitory effect on this IM-IgG activity. Here we describe evidence showing for the first time that the immunosuppressive activity of IM-IgG is aimed at inhibition of interleukin-2 (IL-2) synthesis and does not affect IL-2 receptors.

Tumor therapy of neoplastic diseases with tumor cells and neuraminidase: experimental studies on chessboard vaccination in transplantation tumors

The therapeutic effect of intradermal (i.d.) injection of tumor cells mixed with VCN on growth of spontaneous metastases in transplantable tumors in mice (3-Lewis lung adenocarcinoma; B16-melanoma) and rats (R-3230 mammary adenocarcinoma) was investigated. Intradermal injection was done in a chessboard-like manner; increasing numbers (10(5), 10(6) and 10(7)) of Mitomycin-treated tumor cells (M-TC) were each mixed with increasing amounts (10, 50 and 100 mU) of Vibrio cholerae Neuraminidase (VCN). These different mixtures were injected i.d. at different sites one day after resection of the primary tumor graft to mice and rats, suffering from minimal residual disease. The therapeutic effect of this so-called chessboard vaccination on minimal residual disease was compared to that of the subcutaneous or i.d. injection of VCN-treated M-TC (10(5), 10(6), 10(7) or 10(8) cells) or of single mixtures of M-TC and VCN. The results show that compared to VCN-treated M-TC or single mixtures of M-TC and VCN, chessboard vaccination is the only procedure that is therapeutically effective on metastasation of Lewis lung adenocarcinoma. The therapeutic effect could be abrogated by heat-inactivation of VCN. Incomplete chessboard vaccinations (10(5), 10(6), 10(7) tumor cells, each mixed with 5 mU VCN only) were likewise ineffective. However, treatment with incomplete chessboard vaccinations in combination with a low dose of cyclophosphamide (which is not immunosuppressive, but partly inhibits tumor growth) had a synergistic therapeutic effect on minimal residual disease of Lewis lung adenocarcinoma. In contrast, growth of metastases of B16-melanoma and R-3230 adenocarcinoma could not significantly be influenced by any of those treatments. The DTH response of tumor bearing animals against i.d. applied tumor cells was neither significantly enhanced by the admixture of enzymatically active VCN nor did the DTH response seem to be predictive for a tumor-therapeutic effect. Thomsen-Friedenreich antigens could serologically be detected on untreated cells of Lewis lung adenocarcinoma, B16-melanoma and R-3230 adenocarcinoma. Exposure of Thomsen-Friedenreich antigens after treatment with VCN was enhanced on cells of all tumors except Lewis lung adenocarcinoma. As chessboard vaccination only proved to be successful in Lewis lung adenocarcinoma, but not in the other tumors, it can be concluded that the exposure of Thomsen-Friedenreich antigen plays no decisive role in tumor therapy with tumor cells and VCN. Chessboard vaccination was tolerated without any side effects. Tumor enhancement was not observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Tumour inhibition by interleukin-2 at the tumour/host interface

Until recently, lymphokines were regarded suspiciously as 'ill-defined factors'. Today, however, some of them have been clearly defined in both structural and functional terms. The interleukin-2 (IL-2) molecule and its specific membrane receptors have been the subject of particular attention. Endogenous IL-2 has proved to be an important signal for the activation and expansion of various cell-mediated immunity functions, while exogenous IL-2 has been used to activate numerous cell functions, both in vitro and in vivo, as well as in tumour immunotherapy, both alone or combined with lymphocytes previously activated in vitro (lymphokine-activated killer cells). Adoptive transfer of these cells together with high doses of IL-2 is particularly promising from the clinical standpoint, though by no means free from problems. IL-2 can also be employed in small doses locally in the presence of non-activated lymphocytes from tumour bearing mice to induce a local reaction that subsequently becomes systemic and can lead to the rejection of incipient tumours. Various host immune cells, primarily eosinophils and lymphocytes are involved in this reaction, which can also give rise to tumour-specific immune memory. In this way, the host immune system, despite its inevitable defeat in the first battle against a tumour, may acquire an important role in the long war that lies ahead.

Suppression of interleukin-2 production by macrophages in genetically susceptible mice infected with Leishmania major

Spleen cells from BALB/c mice infected with 2 X 10(7) L. major promastigotes and developing progressive disease produced significantly lower levels of interleukin-2 (IL-2) in response to concanavalin A stimulation than did spleen cells from uninfected mice. In contrast, spleen cells from sublethally irradiated and infected mice, which were able to contain lesion development, produced significantly higher levels of IL-2. The increase in IL-2 production closely paralleled lesion regression. Mice protectively immunized by four intravenous injections with lethally irradiated promastigotes also produced enhanced levels of IL-2, which were sustained after challenge infection. In contrast, spleen cells from BALB/c mice given four s.c. injections of irradiated promastigotes produced high levels of IL-2 before but not after infection. These mice eventually produced levels of IL-2 indistinguishable from those of unimmunized mice with progressive disease. There is thus an inverse relation between disease progression and the ability of spleen cells to produce IL-2. Spleen cells from mice with uncontrolled disease not only produced lower levels of IL-2 but also impaired IL-2 production by normal spleen cells. The ability to inhibit IL-2 was abrogated by passing the cells through a Sephadex G-10 column, removal of plastic adherent cells, and removal of carbonyl iron-ingesting cells. Furthermore, Sephadex G-10 column-treated and plastic adherent, nonspecific esterase-positive spleen cells from mice with progressive disease were able to suppress IL-2 production by normal splenic T cells. The suppressive activity of the adherent cells was not affected by treatment with anti-Thy-1.2 antibody and complement. In contrast, adherent spleen cells from uninfected mice were devoid of such suppressor activity. The depressed IL-2 production by spleen cells from progressively infected mice could be restored to that of normal spleen cells by the addition of indomethacin to the culture. There was however, no correlation between IL-2 production and IL-1 activity in infected or immunized BALB/c mice. Thus, it appears that the suppression of IL-2 production is mediated by prostaglandins elaborated by macrophages from chronically infected mice.