The immunostimulatory actions of cytokines : interactions with endogenous peptides and anti-inflammatory steroids
The effects of the immunomodulatory agents LPS, poly I:C, rabbit EP/IL-1 and the human recombinant cytokines TNF-alpha, IL-lalpha and IL-1alpha were investigated using both in vivo and in vitro model systems. The interactions of these agents with alpha-MSH, dexamethasone, the partially purified supernatant from dexamethasone-stimulated peripheral blood M (DM) and human recombinant lipocortin-1 (hrLC-1) were also studied. Changes in body temperature and plasma PGE2 were measured in rabbits in response to i.v. administration of these agents. Body temperature was measured using rectal thermistor probes. Release of IL-l-like activity and PGE2 were measured from M in vitro. IL-1 was determined using either the lymphocyte proliferation bioassay or an immunoassay. PGE2 was estimated by radioimmunoassay. PLA2 activity was estimated by measuring [14C]-arachidonic acid production from [14C]-phosphatidylcholine. Poly I:C (2.5 g/kg, i.v.), LPS (25 ng/kg), rTNF-alpha (200,000 U/kg, i.v.), rIL-1alpha (2,500 U/kg, i.v.) and rIL-1alpha (500 U/kg, i.v.) were shown to be pyrogenic and to induce increases in plasma levels of PGE2 simultaneously with increases in body temperature. Human rTNF-alpha administered i.v. produced monophasic fevers at low doses 50,000 U/kg and 100,000 U/kg, and a biphasic fever at the higher dose of 200,000 U/kg. Human rIL-1alpha and rIL-1alpha given i.v. produced monophasic febrile responses which were qualitatively similar with both cytokines at all doses used, being rapid in onset, typically within 15 minutes of administration and reaching a maximum after 45 minutes. Based on the TRI2 values 500 U/kg rIL-1alpha (TRI2 = 0.698 0.047 C.h) and 2,500 U/kg rIL-1alpha (TRI2 = 0.73 0.07 C.h) rIL-1alpha appeared to be approximately 5-fold more pyrogenic than rIL-1alpha. alpha-MSH (5 g/kg or 10 g/kg, i.v.) administered after either poly I:C (2.5 g/kg, i.v.), LPS (25 ng/kg, i.v.), rTNF-alpha (200,000 U/kg, i.v.), rIL-1alpha (2,500 U/kg, i.v.) or IL-1alpha (500 U/kg, i.v.) attenuated the febrile response compared to pyrogen alone. alpha-MSH also attenuated the increases in plasma PGE2 levels in response to poly I:C, LPS, rTNF-alpha and rIL-1alpha, however only those in response to LPS and rTNF-alpha were statistically significant. Antipyretic doses of alpha-MSH had no significant effect on either PGE2-induced hyperthermia (500 ng, i.c.v.), normal body temperature or basal plasma levels of PGE2. Dexamethasone (3 mg/kg, i.v.) given 1 h before either TNF-alpha (200, 000 U/kg, i.v.), rIL-1alpha (2,500/U kg, i.v.) or IL-1alpha (500 U/kg, i.v.) significantly attenuated the febrile response compared to responses to pyrogens alone. Dexamethasone pretreatment also attenuated increases in plasma PGE2 levels in response both rTNF-alpha and rIL-1alpha At this dose dexamethasone had no significant effect on normal body temperature or basal plasma PGE2 levels. DM (0.5 ml/kg, i.v.) given 30 min after poly I:C (2.5 g/kg i.v.) attenuated poly I:C-induced fever. TRI5 values were reduced from 3.08 0.37 C.h in response to pyrogen alone to 2.02 0.30 C.h by DM (means s.e. mean for n = 4, P 0.05). Human rLC-I (50 g/kg, i.v.) given immediately before pyrogen significantly attenuated the febrile response to poly I:C (2.5 g/kg, i.v.). TRI5 values were reduced from 4.69 0.51 C.h to 2.66 0.45 C.h by hrLC-1 (means s.e. mean of n = 5, P 0.05). Heating human rLC-I for 30 min at 90 C abolished its antipyretic activity. Human rLC-I (50 g/kg) administered alone had no effect on normal body temperature. Release of IL-1-activity from immunomodulator-stimulated M was time and concentration-dependent. Maximum release occurred after 20 h of incubation in response to 10 g/ml LPS, 1 mg/ml poly I:C and 10 g/ml rTNF-alpha. None of the immunomodulatory agents used appeared to have any direct effect on thymocyte growth. alpha-MSH reduced proliferation of murine thymocytes in response to supernatants from M incubated with either LPS, poly I:C or rTNF-alpha.