Suppression of restraint-induced plasma cytokines in mice pretreated with LPS.

A previous exposure to an inflammatory reaction is known to increase or decrease the activation of the hypothalamic-pituitary-adrenal (HPA) axis induced by a psychological/physical stress. Beside HPA activation, the non- specific responses to these two kinds of stresses involve the immune system including the production of cytokines. Therefore, they could interfere in cytokine production. In order to test this hypothesis, female C3H mice were first injected i.p. with 5 microg of lipopolysaccharide (LPS) or not (C). Eight days later, half of them were submitted to a 4 h-restraint (R) applied during the nocturnal part of the dark-light cycle and sacrificed immediately after (groups LPS-R and C-R), while the non restrained mice stayed in their home cages (groups LPS-C and C-C). Restraint induced an increase in corticosterone production that was not altered by the previous administration of LPS. It had no effect on mitogen-induced lymphoproliferation. However, restraint induced an augmentation of plasma concentrations of interleukin (IL)-1 and IL-6 that was not observed in animals previously exposed to LPS. These results show that restraint, which represents a psychological stress is able to induce the production of plasma cytokines in mice. They also suggest that LPS may induce a long lasting suppression of plasma cytokines through mechanisms that remain to be elucidated.

Physiological significance of the interleukin 1 receptor accessory protein.

Interleukin 1 receptor accessory protein (IL-1RAcP) is an essential signal-transducing component of the IL-1 receptor type I. The recent availability of IL-1RAcP-deficient (KO) mice allows to study the in vivo function of IL-1RAcP. Animals were injected intraperitoneally with rat recombinant IL-1beta (200 ng/mouse), lipopolysaccharide (LPS, 5 microg/mouse), or subjected to 1-hour restraint stress. Neuroendocrine and immune parameters were measured 2 h after IL-1 or LPS injection or just after restraint. In wild-type controls, IL-1 and LPS activated the hypothalamic-pituitary-adrenal axis and increased plasma IL-6. In KO mice, the plasma levels of corticosterone and IL-6 increased after LPS, but not after rat recombinant IL-1beta. The LPS-induced depression of the lymphoproliferation was similar in wild-type and KO mice. Finally, the 1-hour restraint was able to increase the plasma levels of corticosterone in KO mice. These results show that IL-1RAcP is essential for physiological activities of peripheral IL-1, as it was previously demonstrated for those of brain IL-1. However, using IL-1RAcP KO mice, we were unable to demonstrate a specific role of endogenous IL-1 during LPS-induced inflammation. Moreover, stress-induced activation of the hypothalamic-pituitary-adrenal axis may occur in the absence of the IL-1-transducing receptor, IL-1RAcP.

Interleukin 1 receptor accessory protein (IL-1RAcP) is necessary for centrally mediated neuroendocrine and immune responses to IL-1beta.

Mice deficient for the IL-1RAcP gene (IL-1RAcP KO) were used to explore the role of IL-1RAcP in physiological functions of brain IL-1beta. Animals were injected i.c.v. with two different doses of recombinant human (rh) IL-1beta: a small one (750 pg) known to induce sickness behavior, and a larger one (50 ng), chosen to counteract the possible loss of affinity of IL-1beta on its receptor. Neuroendocrine and immune parameters were measured 2 h after IL-1 injection. The increase of plasma corticosterone induced by rhIL-1beta in wild-type (WT) mice was not observed in IL-1RAcP KO mice. Likewise, the depression of splenocyte proliferation occurred in WT but not in KO mice. Finally, in opposition to WT mice, plasma levels and brain cortical content of IL-6 in IL-1RAcP KO mice remained unchanged as compared to saline-injected controls. The results clearly demonstrate that IL-1RAcP is necessary for the induction of the main neuroendocrine and immune effects of central IL-1beta.

Activation of the hypothalamic-pituitary-adrenal axis in IL-1 beta-converting enzyme-deficient mice.

Interleukin-1beta (IL-1beta) plays a key role in immune, behavioral and neuroendocrine responses to inflammation or infection. IL-1beta could also be involved in the response of the hypothalamic-pituitary-adrenal (HPA) axis during stress. Mature IL-1beta derives from a 31-kD precursor (pro-IL-1beta) that is processed by IL-1beta-converting enzyme (ICE). Mice in which the ICE gene has been nullated by homologous recombination were used to investigate the role of IL-1beta in the HPA axis response. Plasma levels of corticosterone and adrenocorticotropic hormone (ACTH) in response to an intraperitoneal injection of 5 microg lipopolysaccharide (LPS) were similar in ICE-deficient mice and wild-type (WT) controls. In contrast, plasma ACTH response to restraint or to 200 ng of rat recombinant IL-1beta (rrIL-1beta) was higher in ICE-deficient mice as compared to WT animals. This hyperreactivity of the HPA axis in ICE knockout mice appears not to be related to the production of plasma IL-1beta or IL-6, which was similar to that of WT mice after rrIL-1beta injection. After lipopolysaccharide, ICE-deficient mice exhibited a smaller increase in plasma-immunoreactive IL-1beta and IL-6 as compared to WT controls. After restraint stress neither increase in plasma IL-1beta nor IL-6 was observed. The mechanisms responsible for the increased reactivity of the HPA axis in ICE-deficient mice may result from a higher sensitivity of the HPA axis to inflammatory cytokines or to cleavage products of pro-IL-1beta processed by non-ICE proteases.

Plasma corticosterone and immune reactivity in restrained female C3H mice.

Psychological stressors are known to stimulate the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system resulting in the release of corticosterone and catecholamines respectively. They have also been reported to induce cytokine production. All these molecules affect various immune parameters and can alter overall immune competence of the individual. The purpose of this investigation was to study the regulation of the production of corticosterone during stress and its possible effects on immune reactivity. In a first series of experiments, the possible regulation of corticosterone production by interleukin (IL)-1beta and peripheral catecholamines during restraint was assessed using a pharmacological approach in mice. Plasma IL-1beta concentrations remained at basal after 1-h restraint and the stress-induced increase of plasma corticosterone was not modified by a peripheral injection of an IL-1 receptor antagonist (IL-1ra). By contrast, chemical sympathectomy potentiated the restraint-induced increase in plasma corticosterone concentration, this potentiation being reversed by IL-1ra. In a second series of experiments, the role of corticosterone in stress-immune relationships was studied in adrenalectomized mice subjected to restraint and immunized with sheep erythrocytes. Non-specific immunity, i.e. proliferation of splenocytes and thymocytes and plasma levels of IL-1beta, as well as specific immunity, i.e. antibody production and delayed hypersensitivity, were not altered after 2-h restraint. Adrenalectomy failed to induce immune effects in stressed animals, except that delayed hypersensitivity was stronger in adrenalectomized animals, revealing that the high levels of corticosterone produced during stress have an anti-inflammatory activity. The present data show that the stress-induced production of corticosterone was modulated by both peripheral catecholamines and IL-1beta. However, this production of corticosterone was unable to modulate immune reactivity except delayed hypersensitivity.

Antibodies directed against a variable and neutralizable region of the HTLV-I envelope surface glycoprotein.

The majority of neutralizing antibodies of HTLV-I are directed against linear epitopes of the envelope surface glycoprotein (gp46) in the immunodominant region 175-199. Although gp46 presents a remarkable degree of conservation, the substitution of the proline at position 192 by a serine is described for 10 isolates among the 54 sequenced ones. This amino acid substitution is known to induce an important change in the orientation of the exposed residues of this region and has drastic consequences on the immunogenicity of the neutralizable epitopes located in this region. We developed monoclonal antibodies directed against epitopes located in this region containing a proline or a serine at position 192. The six monoclonal antibodies obtained recognize the gp46 at the surface of living HTLV-I producing cells, two of them are specific of a 190-197 epitope with a serine at position 192. This demonstrates that the antigenicity of this epitope differs depending on the presence of a proline or a serine at position 192. Altogether, these results demonstrate that the immunodominant neutralizable region 175-199 is antigenically variable.