Regulation of T-cell mixed lymphocyte reaction reactivity: demonstration of enhancing and inhibitory activity in tumor bearing host macrophages supernatants

Tumor modulation of autoreactivity: decreased macrophage and autoreactive T cell interactions

The autologous mixed lymphocyte reaction (AMLR) is an in vitro measure of autoreactivity, a key mechanism in immune homeostasis. In this system, macrophages (M phi) act as accessory cells to autoreactive L3T4+ T cells by presenting self-Ia and releasing soluble modulators. During tumor growth, changes occur in M phi and T cells. Tumor-bearing host (TBH) M phi have a reduced ability to act as accessory cells. In fact, TBH M phi suppressed autoreactivity by 60-70%. The decrease in TBH M phi or T-cell abilities was not due to differences in cell numbers or incubation time. Because tumor growth causes increased prostaglandin E2 (PGE2) production by M phi, indomethacin was used to assess the contribution of prostaglandins. Normal and TBH T-cell reactivity increased nearly 50% when stimulated by normal host M phi, while normal and TBH T-cell reactivity increased nearly 100% when stimulated by TBH M phi. Thus increased prostaglandin production is partly responsible for the increased TBH suppressor M phi activity and in the normal host, suppressor M phi may be responsible for maintaining immune regulation. To assess the direct role of prostaglandins in T-cell hyporesponsiveness, PGE2 was titrated into the cultures. PGE2 suppressed normal and TBH T-cell responsiveness in a dose-dependent manner. Normal host T cells were suppressed to a greater extent than TBH T cells by PGE2 (66% versus 42% suppression, respectively). Reduced Ia expression and active suppressor mechanisms are not the only mechanisms mediating hypoautoreactivity during tumor growth. TBH autoreactive L3T4+ T cells were less responsive to self-Ia; they were only 60-80% as reactive as their normal counterparts. To address whether the helper T (TH)-cell defect involved cytokines, T cells were treated with interleukin (IL)-1, IL-2, and IL-4. In all cases, the TBH T-cell response to the factors was decreased (only 60-75% as reactive as normal T cells). Because TBH M phi-mediated suppression can override the addition of IL-1, IL-2, and IL-4, indomethacin was also added with the exogenous interleukins. This coaddition significantly enhanced normal host autoreactivity above control levels while TBH autoreactivity (the combination of TBH T cells and TBH M phi) only returned to normal host unstimulated levels. Tumor growth modulates the immune response at least by (i) decreasing the accessory cell abilities of TBH M phi through decreased Ia expression and increased production of suppressive molecules such as prostaglandins; and (ii) decreasing the responsiveness to immune enhancing factors by TH cells.

Alteration of macrophage function in AKR/J leukemic mice

Peritoneal macrophages from AKR/J leukemic mice, a strain which spontaneously develops a virally induced T-cell lymphoma between the age of 8-12 months, were used to study any possible changes in adherence, opsonization, phagocytosis, nitroblue tetrazolium (NBT) reduction and antibody-dependent cellular cytotoxicity (ADCC). Increased adherence, opsonization and phagocytosis of particles and impaired ADCC were found when these macrophages were compared with those from tumor-free BALB/c mice. Moreover, phagocytosis and NBT reduction in macrophages from AKR/J leukemic mice were also found to be increased when compared with macrophages from AKR/J mice in their preleukemic stage. The possibility that the decline in ADCC observed, in spite of the fact that the macrophages were activated and showed an increase in other functional aspects, may be responsible for the defective surveillance of macrophages in tumor development is also discussed.

Cytostatic peptide isolation from culture media of mouse peritoneal exudate cells

It was found that the supernatant of mouse PEC culture medium (MCM) (both resident and casein-elicited cells) has an inhibitory effect in vitro on the incorporation of [3H]TdR into DNA of mouse spleen cells. The inhibitory effect in the MCM appears in the first 24 hr and also reaches its maximum value within this time. The inhibitory effect of this factor could not be demonstrated in the extract of freshly harvested M phi cells. The factors responsible for inhibition proved to be heat stable at 80 degrees C for longer than 30 min. Following heat treatment, the crude extract was separated into four fractions absorbing uv light at 280 nm using Sephadex G-25 column chromatography, and the most potent biologically active inhibitory factor was eluted in the last fraction. This fraction could also be obtained with a more effective permeation volume using Trysacryl GF 05 gel chromatography, and the active B fraction from this chromatography could be separated into four subfractions by isotachophoresis (ITP). The active fraction, which was obtained by Trysacryl GF 05 gel chromatography and further separated by ITP, was found to be highly inhibitory. It contained a peptide-like substance with a molecular mass of approximately 2.0 kDa and had an anionic character at pH 4.0. The inhibitory effect of MCM cannot be influenced either by inhibitory compounds of protein synthesis or by proteolysis blocking agents. Furthermore, the inhibitory effect is shown to be reversible and is more pronounced on B cells than on T lymphocytes.

Macrophage-derived prostaglandin E modulation of the mixed-lymphocyte reaction: an anomaly of increased production and decreased T-cell susceptibility during tumor growth

One-way mixed-lymphocyte reactions (MLR) were used to assess macrophage (M phi)-derived factor-mediated modulation of normal and tumor-bearing host (TBH) T-cell immune responsiveness. Normal and TBH M psi culture supernatants contained the inhibitory substance prostaglandin E (PGE) in concentrations of 10(-8) to 10(-9) M, with TBH M phi supernatant containing approximately twice the amount of PGE as its normal counterpart. Normal and TBH MLR reactivity were both suppressed by the addition of normal host M phi supernatant. However, TBH T cells were less inhibited by TBH M phi supernatant (55%) as compared to normal host T cells (73%). Although dialyzed M phi supernatants were less inhibitory (17-19%) on normal host T-cell MLR reactivity, TBH T-cell responses were enhanced (20-46%). Indomethacin or eicosatetraynoic acid treatment of M phi reduced PGE levels in the supernatants and in general enhanced MLR reactivity. When PGE1 and PGE2 were titrated in the MLR, normal host T lymphocytes were more susceptible to inhibition than were TBH. Concentrations of PGE1 and PGE2 comparable to that found in normal host M phi supernatants caused approximately 38% inhibition whereas whole M phi supernatants decreased MLR reactivity by greater than 70%, suggesting that another factor(s) was necessary to account for the additional M phi-mediated suppression of lymphocyte function. Isoelectric focusing was used to fractionate normal host M phi supernatant. Two factors with isoelectric points in the pH ranges 7.0-8.5 and 4.5-5.0 were inhibitory in the MLR. An enhancing factor was also identified with an pI in the range of pH 6.0-7.0. These data suggest that TBH M phi-derived PGE production was increased over its normal counterpart, but that TBH T cells were less susceptible to its effect and an additional factor(s) was working in concert with PGE.

Macrophage depletion and manipulation of enhanced immune response in an animal model of bladder cancer

In a transplantable model of bladder cancer the inhibition of tumor growth by polyinosinic:polycytidylic acid (poly(I:C], concomitant stimulation of natural killer cell activity, and inhibition of both effects by prior inoculation with anti-interferon antiserum have been previously observed. The possible role of macrophages in these interactions is explored. Depletion of peritoneal macrophages by silica at concentrations that did not markedly depress natural killer cell activity was found to inhibit the enhancement of natural killer cell activity by subsequent in vivo poly(I:C) inoculation. Inoculation with silica also seemed to abrogate the tumor inhibitory effect of poly(I:C) treatment. To determine whether effects of poly(I:C) on natural cytotoxicity and tumor growth were mediated through production of interferon, anti-interferon antiserum (alpha-IF) was inoculated prior to poly(I:C) therapy. Tumor growth appeared to be uneffected by this maneuver even though poly(I:C)-induced enhancement of natural cytotoxicity was inhibited. Taken together, both macrophages and interferon may play a pivotal role in the immune response in both a stimulatory and a suppressive capacity. Additional study on such influences may be important if in vivo manipulation of these regulatory effects is to be accomplished successfully.

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.

Evaluation of the immunocompetence of macrophages and the generation of T-cell-mediated cytotoxic response against allogeneic tumor cells in tumor bearers

The present study has examined the competence of peritoneal cells (PC) I of tumor bearers to reverse the immunosuppressive effect of tumor cells, and the ability of the tumor bearers to generate a T-cell-mediated cytotoxic response against allogeneic spleen cells or allogeneic tumor cells. It was found that PC from tumor bearers possess a greater ability to reverse the tumor cell immunosuppression in normal mice. In contrast to normal hosts, the cytotoxic responses of the tumor bearers against allogeneic tumor cells cannot be restored by PC from normal mice or from tumor bearers. The ineffective cytotoxic response in tumor bearers was not due to deficient T responders or T helpers. Rather, it was due to the presence of suppressor cells which were adherent, radioresistant and resistant to anti-Thy-1.2 antibody lysis, and thus were likely to be macrophages. The suppressor macrophages were present only in the spleen and were absent from the peritoneal cavity of the tumor bearers. Their suppressive effect can only be exerted in the presence of tumor cells. These results demonstrate the dichotomy of macrophage function, peritoneal macrophages from the tumor bearers showing increased activity of augmentation of T-cell-response whereas the splenic macrophages cause suppression of the T-cell-response.