Neuropeptides in the immunomodulation: substance P-induced stimulation of immune response in mice

The effects of substance P (SP) and its new structural analog EC-1 administered systemically to CBA mice on the immune responsiveness have been examined. Three main findings are presented in this study. First, the principal effect of SP and EC-1 on the immunity is a stimulatory one. It is shown that in the doses of 1, 10 and 100 mkg/kg of the body weight both neuropeptides significantly increased the number of plaque- and rosette-forming cells in the spleen of animals at the peak of the immune reactions. Second, the destruction of the pituitary stalk prevented the immune response stimulation caused by neuropeptides. Third, SP-induced immunostimulation was not observed after combination with the antagonist of the postsynaptic dopamine (DA) D-2 receptors haloperidol (2 mg/kg) suggesting the involvement of the DAergic system in the realization of this effect. Thus, these results demonstrate neurochemical DAergic mechanisms underlying the immunostimulating influence of tachykinins.

Modulation of the immune response by changing neuromediator systems activity under stress

The possible correction of the immune response affecting the mechanisms of neuroimmunomodulation in the animal model of immobilization stress is considered. Immobilization (3 h on the back) of CBA mice caused a suppression of the immune response. The number of plaque-forming cell (PFC) on the 4th day as well as rosette-forming cell (RFC) number on the 5th day of the immune reaction to sheep red blood cells (SRBC) were found to be reduced as compared to the control. Immunoinhibition in the stressed mice was reversed by the depletion of the cerebral serotonin (5-HT) with p-chlorophenylalanine (PCPA) 2 days before immobilization at a dose of 500 mg/kg. Activation of postsynaptic D-1 and D-2 dopamine (DA) receptors with apomorphine administered 30 min before stress attenuated stress-induced immunosuppression as well. Thus, the immunosuppression elicited by a stressor can be modified by drugs influencing the 5-HT and DAergic systems. It is suggested that the stress-provoked alterations of the immune response can be a consequence of changing neurochemical pattern of the brain and the disturbances of the mechanisms of psychoneuroimunomodulation.

Involvement of delta-opioid receptors in immunosuppression

The present experiments demonstrate that: (1) activation of delta-opioid receptors by a highly selective agonist DSLET leads to immunosuppression, whereas the blockade of these receptors by enkephalin analog ICI 174864 produces immunostimulation; (2) the immunomodulating effect of delta-opioid receptors is mediated by central mechanisms involving the hypothalamus-hypophysis complex; (3) the postsynaptic 5-HT (serotonin) receptors of 5-HT-2 type are involved in the immunoinhibitory action of DSLET. On the other hand, the immunostimulating effect of ICI 174864 is realized with the participation of D-2 postsynaptic DA (dopamine) receptors. It has also been shown that thymus is implicated in the immunostimulating influence of ICI 174864. The data obtained are explained as a result of the interaction of the neuromediator and opioid peptidergic systems in neuroimmunomodulation.

Brain neuromediator systems in the immune response control: pharmacological analysis of pre- and postsynaptic mechanisms

The involvement of the dopaminergic (DAergic), GABAergic and serotoninergic (5-HTergic) synaptic mechanisms in neuroimmunomodulation are considered. It is shown that the central DA- and GABAergic systems exert a stimulatory influence on the immune reactivity. Activation of postsynaptic DA receptors with apomorphine and (+)(3-hydroxyphenyl)-N-n-propylpiperidine [(+)-3-PPP] at high doses, D2 receptor activation with quinpirole, as well as DA reuptake blockade with amantadine and bupropion, resulted in an increase in the immune response. The intensity of the immune response was also increased during activation of the GABAergic system with the GABA agonist muscimol or the benzodiazepine agonists diazepam and tazepam. On the other hand, decreases in the activity of either system by different drugs inhibiting DAergic and GABAergic neurotransmission (antagonists of DA postsynaptic receptors haloperidol at 1.0 mg/kg and (-)-3-PPP at 6.8 mg/kg, agonists of DA autoreceptors apomorphine at 0.02 mg/kg, (-)- and (+)-3-PPP at 1.7 and 3.4 mg/kg, antagonist of GABA receptors bicuculline, blocker of chloride channels picrotoxin, blockers of benzodiazepine receptors Ro 15-1788 and Ro 15-3505) produce suppression of the immune response. The 5-HTergic system is involved in the inhibitory mechanism of neuroimmunomodulation. 5-HT reuptake blockade with 4-(5,6-dimethyl-R-benzophuranil)-piperidine (CGP-6085A) and sertraline led to immunosuppression.

Participation of a GABA-ergic system in the processes of neuroimmunomodulation

Participation of a GABA-ergic system in neuroimmunomodulation was established through the use of a large number of chemical compounds which selectively modulate the activity of the GABA-BD-receptor-ionophore complex. Activation of the GABA-receptors with muscimol or activation of the BD-receptors with diazepam or tazepam had stimulatory effects upon immunogenesis. A decrease in the GABA-BD-receptor-ionophore complex activity led to a suppression of the immune response. The effect was achieved with: a blockade of the complex with bicuculline--a competitive inhibitor of the GABA-receptors: administration of a specific antagonist of the BD-receptors flumazenil or Ro 15-3505: or with blockade of chloride channels with picrotoxin. Activation of the GABA-ergic system causes an increase in bone marrow content of T-helper cells marked by L3T4. The immunomodulatory action of the GABA-ergic system is of central origin and can occur only when the hypothalamo-pituitary system is intact. Section of the pituitary stalk prevents accumulation of the T-helper cells in the bone marrow. The result show that the influence of GABA-ergic system on immunogenesis requires participation of both dopaminergic and serotoninergic systems.

Monoamines as immunomodulators: importance of suppressors and helpers of the bone marrow

The intraimmune pathways and mechanisms of action of the serotoninergic and dopaminergic systems in exerting a modulating effect upon immunogenesis are presented. Experiments were carried out in mice immunized with sheep red blood cells (1 X 10(7); 5 X 10(6)). Participation of the hypothalamic-pituitary complex in the monoaminergic mechanisms of stimulation and inhibition of rosette formation was revealed. Dissection of the pituitary stalk prevented stimulation of rosette formation by apomorphine (1 mg/kg i.p) and bupropion (20 mg/kg) and the reduction of the immune response by haloperidol (1 mg/kg), 5-hydroxytryptophan (300 mg/kg) and serotonin (50 mg/kg). The results of syngeneic cellular transfer of different immunocompetent organs showed that serotonin injection induced an increase in B-suppressor activity of bone marrow cells, reaching maximal value in the inductive period (day 3 of the immune response). B-Lymphocyte suppression in donors not treated with serotonin peaked on day 5 of the immune response. Stimulation of the immune response under activation of the dopaminergic system after apomorphine administration was provided by an increase in T-helper activity in the bone marrow cells, mainly with respect to IgM-response. The suppressive activity of bone marrow T cells on IgM- and IgG-immune responses was increased in nonimmunized donors treated with serotonin or haloperidol. The mechanisms of neurochemical multichannel immunomodulation by means of redistribution of cellular populations resulting in an increase in suppressors or helpers in bone marrow are discussed.

5-Hydroxytryptophan effect on the development of the immune response: IgM and IgG antibodies and rosette formation in primary and secondary responses

In animals immunized with bovine serum albumin, 5-hydroxytryptophan prolonged the latent period of the IgM and IgG primary responses, decreased response intensity, delayed the response peak and suppressed IgG immunological memory. In 5-hydroxytryptophan-treated mice, the number of rosette-forming cells (RFC) in the lymph node and spleen decreased during the primary and secondary responses. This effect was due to the decreased number of IgG RFC and to the later involvement of IgM RFC in the immune response. The absence of the secondary response was related to unprimed IgG memory cells. 5-hydroxytryptophan does not inhibit the primary and secondary responses after the connections between the hypothalamus and pituitary have been disrupted. The participation of the n.raphe-hypothalaminc-pituitary system in immuno-regulation and the putative mechanism underlying serotonin effect on the immune response are discussed.