Interleukin-1 production by immunologically hyporeactive tumour-bearing mice

The effects of cyclooxygenase inhibitors on tumor-induced anorexia in rats

BACKGROUND

Interleukin-1 (IL-1) and tumor necrosis factor (TNF) are potent induces of prostaglandin (PG) synthesis and injection of PGE, IL-1, or TNF decreases food intake in healthy animals, whereas the anorexigenic effects of injected IL-1 and TNF are blocked by inhibitors of PG synthesis. It has been hypothesized that host secretion of IL-1 and TNF contribute to tumor-induced anorexia. This study was undertaken to determine whether administration of PG inhibitors alters food intake in anorectic rats implanted with Walker 256 carcinoma.

METHODS

Groups of six tumor-bearing rats were implanted with slow-release pellets containing ibuprofen, indomethacin, or acetylsalicylic acid. Food intake, tumor growth, and body temperature were monitored for 14 days and compared with control tumor-bearing animals implanted with placebo pellets.

RESULTS

Tumor growth was associated with anorexia, fever, weight loss, and increased leukocyte secretion of IL-1 and TNF. Indomethacin and ibuprofen retarded tumor growth 30-40% and lowered body temperature compared with controls, but had no effect on food intake or body weight of tumor-bearing animals.

CONCLUSIONS

Prostaglandins do not mediate tumor-induced anorexia.

Exogenous interleukin-2 abrogates differences in the proliferative responses to T cell mitogens among inbred strains of mice

The proliferative response of spleen cells from BALB/c mice to stimulation with a T cell mitogen, concanavalin A (Con A), was two or more times stronger than that of cells from C57BL/10SnSc (B10) mice. In contrast, the cells from B10 mice responded better to B cell mitogen bacterial lipopolysaccharide (LPS). The differences in the proliferative response to Con A stimulation were not associated with the function of macrophages nor did they depend on IL-1. Spleen cells from BALB/c and B10 mice synthesized comparable amounts of mRNA for IL-1 alpha, and the production of biologically active IL-1 was even higher in the B10 strain. Indomethacin, an inhibitor of prostaglandin synthesis, had no effect on the differences in reactivity between the cells from BALB/c and B10 mice. In addition, no differences in the synthesis of mRNA for the inducible 55-kDa interleukin-2 (IL-2) receptors were found between the spleen cells from BALB/c and B10 mice. However, Con A-stimulated spleen cells from B10 mice produced a significantly lower amount of biologically active IL-2 than similarly stimulated cells from BALB/c mice. In the presence of exogenous IL-2, these low responder spleen cells from the B10 mice responded by proliferation to Con A stimulation to the same extent as cells from the BALB/c mice. These results thus show that a low proliferative response to Con A stimulation in B10 mice was a consequence of a lower production of IL-2 and possibly abrogated the proliferative hyporeactivity produced by exogenous IL-2. We suggest that the differences in the ability to produce IL-2 could be a reason for the discrepancies observed in the immunological responsiveness between BALB/c and B10 mice.

Inhibitory versus stimulatory effects of natural human interferon-alpha on proliferation of lymphocyte subpopulations

Highly purified natural human interferon-alpha (IFN-alpha) inhibited in a dose-dependent manner the proliferation of human peripheral blood lymphocytes (PBL) stimulated with T-cell mitogen concanavalin A (Con A) or with interleukin-2 (IL-2). Contrary to this inhibitory effect, IFN-alpha at the same concentrations significantly increased proliferation of PBL stimulated with B-cell mitogen bacterial lipopolysaccharide (LPS) or with IL-3, and even spontaneous proliferation of PBL was enhanced by IFN-alpha. Proliferation of Con A-stimulated PBL depleted of CD8+ cells was sensitive to the inhibitory action of IFN-alpha, while proliferation of the Con A-stimulated CD4+ cell-depleted PBL was not affected by IFN-alpha. The inhibitory effect of IFN-alpha on PBL proliferation was due to neither inhibition of IL-2 receptor (IL-2R) expression, activation of suppressor cells, nor inhibition of lymphokine production. Rather, IFN-alpha augmented production of IL-1 and IL-2 by PBL. These results show that the suppressive effect of natural IFN-alpha on Con A-induced proliferation of PBL is due to a direct growth-inhibitory effect on CD4+ T cells, and that IFN-alpha simultaneously augments production of lymphokines. This could in turn lead to the increased proliferation of IFN-alpha-resistant cell populations.

Natural human interferon-alpha augments interleukin-2 production by a direct action on the activated IL-2-producing T cells

The production of interleukin-2 (IL-2) by Concanavalin A (ConA)-stimulated peripheral blood leukocytes (PBL) from normal human donors was enhanced by natural human interferon-alpha (IFN-alpha). The mechanism of the action of IFN-alpha on IL-2 production was studied further using cloned human leukemic T-cell lines, which produce IL-2 spontaneously and/or after mitogen stimulation. It was found that IFN-alpha alone did not stimulate IL-2 production, but increased it in the activated cells. The ability of IFN-alpha to increase IL-2 production was abrogated by the treatment of IFN-alpha preparations with specific anti-IFN-alpha antibody, and the induced IL-2 activity was completely inhibited by monoclonal antibody against human IL-2. We suggest that the augmentation by IFN-alpha of IL-2 production in the activated T cells may be one of the mechanisms attributable to the immunotherapeutic action of IFN-alpha.