Yuzo Okumura

Kupffer Cells May Autoregulate Interleukin 1 Production by Producing Interleukin 1 Inhibitor and Prostaglandin E2

Rat Kupffer cells stimulated with bacterial lipopolysaccharide (LPS) produced high levels of interleukin 1 (IL‐1), as determined by thymocyte proliferation assay. Indomethacin revealed a dose‐dependent augmentation in IL‐l production, in parallel with a dose‐dependent reduction in prostaglandin E2 production by Kupffer cells. The addition of exogenous prostaglandin E2, dibutyryl cAMP, or isoproterenol led to a dose‐dependent suppression of IL‐I production. The supernatant from UPS‐stimulated Kupffer cells also contained factors that Inhibited IL‐1‐induced thymocyte proliferation. Upon gel filtration, two inhibitory peaks, at apparent MW of 27,000 and 6000, were obtained. The latter but not the former fraction also affected Interleukin 2 (IL‐2)‐induced thymocyte proliferation. Increasing amounts of IL‐1 overcame the inhibitory activity derived from the 27,000 MW fraction. These results suggest to us that prostaglandin E2 and IL‐1 inhibitor released by Kupffer cells may be involved in negative self‐control in regulating IL‐1 production and its action.

Selective partial IgM deficiency:functional assessment of T and B lymphocytes in vitro

Seven patients with selective IgM deficiency (SIgMD) were studied for cell surface immunoglobulin (SmIg), T-cell subpopulations, and immunoglobulin (Ig) synthesisin vitro by peripheral blood lymphocytes (PBL). Serum IgM levels were less than 25 mg/dl, while IgA, IgG, and IgD were within normal levels. The patients had respiratory or urinary tract infections and two were diagnosed as having systemic lupus erythematosus (SLE). T/B-cell ratios in PBL were within normal ranges. Percentage ratios of B cells bearing SmIg were normal in five patients and decreased in two; however, normal values were seen after 7 days of culture in the presence of PWM. OKT4/OKT8 ratios decreased in five of seven patients, in whom two were due to a decrease in OKT4 and two to an increase in OKT8 cells. One showed a decrease in OKT4 and an increase in OKT8. Analysis of lymphocyte function for Ig synthesisin vitro, using a coculture of counterpart T and B cells from healthy individuals and patients with SIgMD, revealed that the increased function of IgM isospecific suppressor T cells (Ts) was responsible for the IgM deficiency in all seven patients.

Kupffer cells modulate natural killer cell activity in vitro by producing prostaglandins

The effect of Kupffer cells on natural killer (NK) cell-mediated cytotoxicity was examined. Kupffer cells prepared from rat liver suppressed NK activity against K562 cells and other tumor cell lines through a soluble factor secreted into the culture supernatant. When human peripheral blood mononuclear cells were incubated with the Kupffer cell-culture supernatant, a significant reduction of the cytotoxic activity was observed in the 6-hr chromium-release assay. This activity was dose dependent and was evident at various effector/target cell ratios. Lipopolysaccharide stimulated generation of the suppressive factor released from Kupffer cells in a dose-dependent manner. Suppression of the NK activity was observed when the Kupffer cell-culture supernatant was present in the assay system, whereas pretreatment of effector/target cells with the supernatant had minimal inhibitory effects. Autologous monocytes in human peripheral mononuclear cells were not related to this suppression. The suppressive factor in the fraction had a molecular weight below 10,000. Indomethacin, an inhibitor of prostaglandin synthesis, ameliorated the suppressive effects. These results suggest that Kupffer cells may modulate NK activity by producing PGs (E1, E2, and F2 alpha).

Human lymphocytes synthesize C-reactive protein

We obtained evidence for the synthesis and secretion of C-reactive protein (CRP) by peripheral mononuclear cells in culture. Human mononuclear cells isolated from peripheral blood, after depletion of platelets, were cultured in giutamine-depleted RPMI 1640 supplemented with [3H]glutamine in the presence of 10-O-tetradecanoyl-phorbol-13-acetate (TPA). Anti-CRP antiserum was added to the culture medium, and the resultant immunoprecipitate was analyzed in SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The immunoprecipitate consisted of CRP, heavy and light chains of IgG, and only the CRP protein band had radioactivity, indicating that CRP was synthesized by mononuclear cells. In the populations of mononuciear cells, T-cell preparations mainly synthesized CRP, under stimulation of a factor derived from activated monocytes. Studies using the inhibitors of phospholipid metabolism suggested that generation of the monocyte factor was relevant to metabolites of an arachidonate cascade.

Influence of acute-phase proteins on the activity of natural killer cells

The effects ofα1-antitrypsin (α1,-AT),α1,-acid glycoprotein (α1AGP), and haptoglobin (Hp), the main constituents ofα-globulin and which belong to acute phase proteins, on NK activity were examined using K562 cells as the NK target cells. Among the three proteins,α1,-AT andα1AGP had inhibitory effects on NK activity for “fast target” K562 cells. Theα,-AT preparations having the same protein concentration and a different trypsin inhibitory capacity (TIC) had an equal effect. Althoughα1AT andα1,-AGP equally reduced the NK activity, the mechanism involved in the reduction differed, in that the effect ofα1,-AT directed toward NK cells reduced their binding capacity with the target cells,α1,-AGP probably interacts with a cytotoxic factor secreted from NK cells following effector-target interaction. These studies suggest that each of the acute-phase proteins, which increase following inflammation, inhibits NK cell function by two distinct mechanisms.