Hematopoietic reconstitution after lethal irradiation and bone marrow transplantation: effects of different hematopoietic cytokines on the recovery of thymus, spleen and blood cells.

Lethally irradiated mice were grafted with syngeneic bone marrow cells or left ungrafted. Mice of each group were injected with different hematopoietic cytokines for 5 consecutive days starting immediately after irradiation or left uninjected. The recovery of lymphoid tissues induced by hematopoietic cytokines 7 days after irradiation and bone marrow cell transplantation was comparable to that observed at days 21-28 in irradiated, bone marrow-grafted, but cytokine-uninjected mice. IL-11 or IL-6, in combination with IL-3, was able to hasten thymus, spleen and blood cell numbers and functions. SCF also displayed a detectable effect when used with IL-3. Conversely, the IL-6 superagonist K-7/D-6 was able, when injected alone, to induce significant recovery of thymus, spleen and blood cells. Thus, K-7/D-6 appears to be a most efficient cytokine for fast reconstitution of lymphoid tissues after irradiation and bone marrow transplantation.

Use of hematopoietic cytokines to accelerate the recovery of the immune system in irradiated mice.

In our previous studies aimed at designing appropriate strategies to accelerate recovery of the immune system after irradiation, we found that the hematopoietic cytokine recombinant murine (rmu) interleukin (IL)-3 was able to induce differentiation and growth of thymocytes and splenic T and B lymphocytes in mice exposed to x-rays (200-500 cGy). The recovery, however, was complete at 7 days only after a dose of 200 cGy, whereas 2, 3, and 4 weeks were necessary to achieve full recovery after 300, 400, and 500 cGy, respectively. These studies were extended to investigate the effects of another hematopoietic cytokine, recombinant human (rhu) IL-11, a bone marrow stromal-derived cytokine, administered together with IL-3 to irradiated mice. The synergistic effect of the two cytokines was evident when relatively small doses of rhu IL-11 were injected with an optimal dose of rmu IL-3.

IL-11 synergizes with IL-3 in promoting the recovery of the immune system after irradiation.

In our previous studies aiming at the design of appropriate strategies to accelerate the recovery of the immune system after irradiation, we found that recombinant murine (rmu) IL-3 treatment induces differentiation and growth of thymocytes and splenic T and B lymphocytes in mice exposed to X-rays (200-500 cGy). These studies were extended to investigate the effects of recombinant human (rhu) IL-11. Results indicate that rhuIL-11 is able to restore thymus and spleen cell numbers as well as T and B cell mitotic responsiveness in mice exposed to 200 cGy but not to 300 cGy. However, recovery of thymus and spleen cell numbers and functions could be accelerated also in mice exposed to higher dose if rhuIL-11 was given with rmuIL-3. Recovery was complete as soon as 7 days after irradiation. A large dose of both cytokines was explored and the synergistic effect of the two cytokines was evident when a relatively small dose of rhuIL-11 was injected with graded doses of rmuIL-3. The recovery of the immune system in irradiated mice injected with these cytokines was independent from Bcl-2 expression, suggesting that elimination of damaged cells by apoptosis is unaffected by hematopoietic cytokines.

Dopamine D1 receptors in the amygdala enhance the immune response in the rat.

Indirect evidence suggests that dopamine within the brain may participate in the regulation of immune responses in both man and rodents. The aim of the present study was to investigate the possible role played by the specific dopamine D1 receptor subtype within the central amygdala in the modulation of immunity. Mitogen responsiveness of splenocytes and NK cell activity were measured in rats following local microinfusion of SKF 38393, a specific dopamine D1 receptor agonist. Microinfusion of SKF 38393 (100 nmol) within the central amygdala increased the proliferative response of splenocytes to Con A, whereas it did not modify the proliferative response of splenocytes to LPS or NK cell activity. The effects of SKF 38393 were prevented by prior systemic administration of SCH 23390 (0.3 mg/kg ip), a specific D1 receptor antagonist. These results indicate that activation of dopamine D1 receptors within the central amygdala induced selective stimulation of mitogen responsiveness of splenocytes and suggest that specific activation of dopamine neurotransmission within selected areas of the limbic system may produce immunoenhancing effects. These findings further confirm the immunomodulatory role played by dopaminergic mechanisms in the brain.

Evidence for an involvement of dopamine D1 receptors in the limbic system in the control of immune mechanisms.

Indirect evidence suggests that dopamine within the brain may participate in the regulation of immune responses both in humans and in rodents. The aim of the present study was to investigate the possible modulatory role played by specific dopamine D1 receptor subtypes within discrete sites of the brain dopaminergic pathways. Mitogen responsiveness of splenocytes and natural killer (NK) cell activity were measured in rats following microinfusion of SKF 38393, a specific dopamine D1 receptor agonist, into the ventral tegmental area, the amygdala, the nucleus accumbens and the CA1 area of the hippocampus. We report here that microinfusion of SKF 38393 (100 nmol) within the central amygdala increased the proliferative response of splenocytes to concanavalin A (ConA) while it did not modify the proliferative response of splenocytes to lipopolysaccharide (LPS) or NK cell activity. On the contrary, microinfusion of SKF 38393 into the nucleus accumbens decreased the proliferative response of splenocytes to ConA and LPS, while NK cell activity remained unchanged. Similarly, microinfusion of SKF 38393 into the CA1 area of the hippocampus decreased the proliferative response of splenocytes to LPS, but not to ConA and did not affect NK cell activity. Finally, microinfusion of SKF 38393 into the ventral tegmental area did not significantly modify the proliferative response of splenocytes to either ConA or LPS and did not affect NK cell activity. All immunological changes evoked through the different areas of the brain following microinfusion of SKF 38393 were prevented by systemic administration of SCH 23390, a specific D1 receptor antagonist.

Corticotropin-releasing factor microinfused into the locus coeruleus produces electrocortical desynchronization and immunosuppression.

In freely moving rats with cannulae chronically implanted into the locus coeruleus (LC), the effects of corticotropin-releasing factor (CRF) on electrocortical (ECoG) spectrum power activity and on immune mechanisms (splenocyte mitotic response to concanavalin A, Con A, and lipopolysaccharide, LPS, natural killer cell, NK, activity) were assessed. CRF (100-300 ng) microinfused into the LC produced marked ECoG desynchronization characterized by a significant decrease in total voltage power as well as in power of frequency bands of 0.25-3 and 3-6 Hz. These effects lasted 30-60 min according to the dose. A prior administration of alpha-helical CRF(9-41) (200 ng into the LC 15 min before) prevented ECoG desynchronization induced by CRF (100 ng). In addition, CRF (100 ng) given into the LC produced a significant decrease 45 min later in the splenocyte proliferative response to Con A and LPS and a significant fall of NK activity. These effects were prevented by prior microinfusion into the same site of alpha-helical CRF (200 ng). In conclusion, the present experiments show that CRF given into the LC produces an intense state of ECoG desynchronization accompanied by marked immunodepression and suggest that LC is an important site in the brain through which CRF exerts its immunosuppressive activity.

A reappraisal of the role of the various opioid receptor subtypes in cell-mediated immunity.

Opioid peptides have been shown by several studies to modulate various parameters of the immune response, but scant experimental findings exist on the role played by specific opioid receptor subtypes in the control of immune mechanisms. This study focuses on the in vitro influences of [Trp4,Asn7]dermorphin, a mu-selective agonist, [D-Ala2]deltorphin I, a delta-selective agonist and U50,488, a kappa-selective agonist, on the proliferative response of splenocytes to concanavalin A (Con A). [Trp4,Asn7]dermorphin at low concentrations (10(-11P) and 10(-12) M) enhanced the proliferative response to Con A, whereas higher concentrations (10(-6) to 10(-7) M) inhibited it. Both effects were antagonized by naloxone. [D-Ala2]deltorphin I at very low concentrations (10(-12) to 10(-13) M) also produced a significant increase in the proliferative response of splenocytes to Con A. This effect was significantly antagonized by natrindole, a specific delta-receptor antagonist. Finally U50,488 at concentrations ranging from 10(-8) to 10(-9) M inhibited the proliferative response to Con A. The effects of U50,488 were mediated by the stimulation of the kappa-opioid receptors, since a preincubation of splenocytes with the selective antagonist norbinaltorphimine significantly reduced or abolished the U50,488-induced suppression of the mitotic response. In conclusion, our results clearly indicate that the different opioid receptor subtypes play a different role in the control of immune mechanisms and suggest that immunoenhancing effects of opioid peptides are very likely due to the stimulation of mu- and delta-receptors, whereas the immunosuppressive effects are mediated through the stimulation of kappa-opioid receptors.

Evidence that CRH microinfused into the locus coeruleus decreases cell-mediated immune response in rats.

Rat/human-corticotropin-releasing hormone (CRH) microinfused unilaterally into the locus coeruleus (LC) of awake, chronically cannulated rats produced intense behavioral stimulation accompanied by a marked decrease of the proliferative response of splenocytes to Con A and LPS and natural killer activity. These effects were specifically prevented by prior administration into the same site of the CRH antagonist (alpha-helical CRH [9-41]). The present results confirm that a strict relationship exists between the CNS and cell-mediated immunity; in addition, they also indicate that CRH produces its behavioral and immune changes by an interaction with specific receptors and that one of the main sites through which CRH exerts these effects is represented by the LC.