Prostaglandins and the modulation of immunological responses

Absence of systemic oxidative stress and increased CSF prostaglandin F2α in progressive MS

OBJECTIVE

We aimed to investigate the role of oxidative stress in the progression of multiple sclerosis (MS).

METHODS

We determined by liquid chromatography-tandem mass spectrometry nonenzymatic (F2-isoprostanes) and enzymatic oxidation products of arachidonic acid (prostaglandin F2α [PGF2α]) in plasma and CSF of 45 controls (other neurologic disease [OND] with no signs of inflammation) and 62 patients with MS. Oxidation products were correlated with disease severity and validated biomarkers of inflammation (chemokine ligand 13; matrix metalloproteinase-9; osteopontin) and axonal damage (neurofilament light protein).

RESULTS

Compared with OND controls, plasma concentrations of F2-isoprostanes and PGF2α were significantly lower in patients with progressive disease, and decreased with increasing disability score (Expanded Disability Status Scale). In contrast, CSF concentrations of PGF2α, but not F2-isoprostanes, were significantly higher in patients with progressive disease than OND controls (p < 0.01). The content of PGF2α in CSF increased with disease severity (p = 0.044) and patient age (p = 0.022), although this increase could not be explained by age. CSF PGF2α decreased with natalizumab and methylprednisolone treatment and was unaffected by the use of nonsteroidal anti-inflammatory drug in secondary progressive MS. CSF PGF2α did not associate with validated CSF markers of inflammation and axonal damage that themselves did not associate with the Expanded Disability Status Scale.

CONCLUSIONS

Our data suggest that MS progression is associated with low systemic oxidative activity. This may contribute to immune dysregulation with CNS inflammation accompanied by increased local cyclooxygenase-dependent lipid oxidation.

A study on plasma prostaglandin E2 levels in hepatitis B carriers and patients with chronic active hepatitis

Prostaglandin E2 (PGE2), one of the major prostaglandins synthesized in human monocyte and macrophage, is able to modulate T lymphocyte reactivity, such as lymphokine secretion and cytotoxicity. Some immunologic abnormalities such as alteration in the synthesis of PGE2 by monocyte and macrophage or in the response of T lymphocytes to PGE2 can be found in clinical disease.

We measured the plasma PGE2 level in the control group and patients with chronic liver disease.

The results were obtained as follows. The mean plasma PGE2 level was 2.65 ± 0.69 pg/ml in the control group. The mean plasma PGE2 level was 9.07 ± 5.89 pg/ml in 15 patients with chronic active hepatitis and was significantly higher than that of the control group (p<0.01). The plasma mean PGE2 level was 4.65 ± 1.59 pg/ml in 8 patients in the healing stage or stable stage of chronic hepatitis and was tend to decrease. However, this decrease is significantly different from that of the control group. The plasma PGE2 level was 3.5 ± 0.92 pg/ml in 4 hepatitis B carriers and was not significantly different from that of the control group (p<0.05).

This results suggest that plasma PGE2 can be used for the measurement of cell-mediated immunity and follow-up study in patients with chronic active hepatitis and hepatitis B carriers.

Lithium and immune function

Lithium has potent antiviral and immunostimulating properties which are probably consequences of its actions on prostaglandin synthesis. Although lithium has considerable potential in the prophylaxis of some viral illnesses and other manifestations of defective immune function, it is, paradoxically, capable of activating autoimmune mechanisms in predisposed patients.

Role of adrenal hormones and prostaglandins in the control of mouse thymocytes lysis

The cytolytic actions of glucocorticoids and of agents increasing cyclic AMP were studied in vitro in thymocyte suspensions isolated from adrenalectomized or hydrocortisone-treated mice. Although considered as corticoresistant cells, the thymocytes isolated from hydrocortisone-treated mice were lysed to the same extent although more slowly in vitro by dexamethasone than whole thymocyte populations (i.e. corticosensitive cells). Moreover, these two cell populations were shown to contain comparable amounts of glucocorticoid receptors and to be almost equally sensitive to the metabolic effects of glucocorticoids when measured by inhibition of RNA and DNA synthesis. Studies performed with corticosensitive cells showed that prostaglandin E2, isoproterenol and dibutyrilcyclic AMP were also able to induce cell lysis and that, isoproterenol and dexamethasone exerted additive cytolytic action in vitro. In vivo experiments showed also an additive effect of steroids and isoproterenol on thymus atrophy. In contrast, cells isolated from hydrocortisone-treated animals were not sensitive to the cytotoxic action of prostaglandin E2, isoproterenol and dibutyril cyclic AMP. This difference between the two populations was not associated with any difference in the responsiveness of adenylate cyclase as determined following isoproterenol-induced accumulation of cyclic AMP. The cytolytic action of dexamethasone but also that of prostaglandin E2 and isoproterenol, could be blocked in the presence of cycloheximide, an inhibitor of protein synthesis, thus suggesting that glucocorticoids and agents increasing cyclic AMP control the synthesis of some proteins involved in the triggering of cell lysis. Among the hypotheses proposed to explain the differences between in vitro and in vivo sensitivity of lymphoid cell to glucocorticoids, it was suggested that the drug may in vivo indirectly control the viability or the proliferation of thymocytes through the release of other mediators. We have shown that in vivo injection of hydrocortisone induces an accumulation of fatty acids in the whole thymus gland but not in the isolated thymocytes. Since exogenous fatty acids exert cytolytic actions on isolated thymocytes, we suggest that glucocorticoids may exert in vivo an indirect toxic action by promoting the release of fatty acids from adipose tissue or other sources.

Prostaglandin secretion by human thymic epithelium: in vitro effects of steroids

Increasing evidence suggests a role for prostaglandins in the immune response. As steroids have been shown recently to modulate prostaglandin secretion, we have studied the secretion of prostaglandin and the effect of various steroids in culture of human thymus epithelial cells. Using reverse phase high pressure liquid chromatography and radioimmunoassays, we have shown that these cells produce substantial amounts of PGE2 and PGF2 alpha and that this secretion is modulated by steroid hormones. Prostaglandin could represent one of the factors of the thymic environment which respond to steroid hormones.

Antibodies against extractable components from Propionibacterium acnes in humans with and without acne vulgaris

Acidic polysaccharides (AP) are released from Propionibacterium acnes I and II during growth. Similar antigens are released from two strains of P. avidum, but in a smaller amount. Furthermore, prostaglandin-like substances (PLS) have been isolated from the lipid fraction of P. acnes. The AP antigens give rise to a precipitation reaction against a large proportion of normal sera. However, significantly higher antibody titre levels towards the AP fraction were found in patients with severe acne vulgaris. No rise of antibodies was found towards PLS. These findings suggest that AP's may contribute to the inflammatory response in acne vulgaris as antigens, whereas PLS, as one of the potential mediators trigger development of the initial lesions.

Prostaglandin E2 as a modulator of macrophage-T lymphocyte interactions

Sufficient data exist to implicate the monocyte-macrophage as the major source of prostaglandins in monocyte-macrophage-T lymphocyte interactions. Prostaglandin (PG) E2, a major prostaglandin synthesized by human monocyte-macrophages is able to modulate a variety of T lymphocyte reactivities including blastogenesis, lymphokine secretion, and cytotoxicity. The effect of PGE2 on T lymphocyte function varies according to the primary activating stimulus, the specific response under investigation, as well as the population of T lymphocytes involved. Some immunologic abnormalities found in clinical disease may in part derive from alterations occurring in the synthesis of PGE2 by monocyte-macrophages or in the response of T lymphocytes to PGE2.

Endogenous prostaglandin synthesis and the control of lymphocyte function

Prostaglandins serve an important regulatory role in immune responses. Much of their activity seems to involve regulating the early stages of lymphocyte or macrophage activation. Besides the capacity of prostaglandins to control lymphocyte activation directly by blocking transformation, at least one type, PGE2 can induce a class of glass-adherent T-cells to produce a suppressive peptide in vitro. The data we have obtained suggest the existence of a feedback loop in which PG production by an activated T-cell serves as the signal that induces a second T-cell to release a suppressor peptide. This peptide can then regulate the ability of the activated T-cell to pass through the cell cycle. Other examples of feedback loops have recently been postulated or shown to exist among immunocompetent cells. It remains to be shown how these various regulatory loops combine to form the integrated network that modulates immunoresponsiveness.

Synthesis of prostaglandins by subpopulations of human peripheral blood monocytes

The ability of monocytes/macrophages to regulate various aspects of immunologic responses may in part depend on their release of soluble substances such as prostaglandins. Using quantitative gas-liquid chromatography/mass spectrometry, prostaglandin E2 was found to be the major prostaglandin synthesized in culture by human peripheral blood monocytes. Subjecting these cells to discontinuous density gradient fractionation demonstrated significant differences in the synthesis of prostaglandins E2 and E1 among the resulting monocyte subpopulations.

Noncorticosteroidal anti-inflammatory agents in Ophthalmology

Efforts have been made to develop noncorticosteroidal anti-inflammatory therapy. The goals of such therapy have been to eradicate the primary cause, prevent the initial tissue injury, moderate inflammatory response, and enhance tissue repair while minimizing and eliminating the undesirable aspects of the therapy.