AlaskaDenise
In Memoriam
Production of interleukin-6 in contracting human skeletal muscles can account for the exercise-induced increase in plasma interleukin-6
Adam Steensberg,*? Gerrit van Hall,* Takuya Osada,* Massimo Sacchetti,* Bengt Saltin,* and Bente Klarlund Pedersen*?
*The Copenhagen Muscle Research Centre, University of Copenhagen, Copenhagen, Denmark
?The Department of Infectious Diseases, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
Corresponding author B. Klarlund Pedersen: The Department of Infectious Diseases and The Copenhagen Muscle Research Centre, Rigshospitalet 7652, Blegdamsvej 9, DK-2100 Copenhagen N, Denmark. Email:bkp@rh.dkReceived July 31, 2000; Accepted September 21, 2000.
Abstract
1.Plasma interleukin (IL)-6 concentration is increased with exercise and it has been demonstrated that contracting muscles can produce IL- The question addressed in the present study was whether the IL-6 production by contracting skeletal muscle is of such a magnitude that it can account for the IL-6 accumulating in the blood.
2.This was studied in six healthy males, who performed one-legged dynamic knee extensor exercise for 5 h at 25 W, which represented 40% of peak power output (Wmax). Arterial-femoral venous (a-fv) differences over the exercising and the resting leg were obtained before and every hour during the exercise. Leg blood flow was measured in parallel by the ultrasound Doppler technique. IL-6 was measured by enzyme-linked immunosorbent assay (ELISA).
3.Arterial plasma concentrations for IL-6 increased 19-fold compared to rest. The a-fv difference for IL-6 over the exercising leg followed the same pattern as did the net IL-6 release. Over the resting leg, there was no significant a-fv difference or net IL-6 release. The work was produced by 2.5 kg of active muscle, which means that during the last 2 h of exercise, the median IL-6 production was 6.8 ng min−1 (kg active muscle)−1 (range, 3.96-9.69 ng min−1 kg−1).
4.The net IL-6 release from the muscle over the last 2 h of exercise was 17-fold higher than the elevation in arterial IL-6 concentration and at 5 h of exercise the net release during 1 min was half of the IL-6 content in the plasma. This indicates a very high turnover of IL-6 during muscular exercise. We suggest that IL-6 produced by skeletal contracting muscle contributes to the maintenance of glucose homeostasis during prolonged exercise.
(snip)
DISCUSSION
The present study demonstrates that during exercise the net skeletal muscle IL-6 production increases strikingly and can account for the exercise-related high plasma IL-6 concentration. It is noteworthy that the large elevation in IL-6 was the result of exercise performed by only 2.5 kg of muscle, which during the last 2 h of exercise produced 6.8 ng IL-6 min−1 (kg muscle)−1 (3.96-9.69 ng min−1 kg−1).
When comparing the release of IL-6 from the contracting muscle with the amount accumulated in the body, it is quite apparent that the release markedly surpassed the rate of accumulation. The increase in arterial plasma IL-6 concentration during the last 2 h of exercise was 10.04 ng l−1 (8.30-12.00 ng l−1). Assuming that the IL-6 produced is diluted in the extracellular space (12 l), the total amount of IL-6 accumulated during the last 2 h of exercise was about 120.48 ng (99.60-144.08 ng) or 1.00 ng min−1 (0.83-1.20 ng min−1). This implies that the net release of IL-6 from the active leg was ≈17-fold higher than the rate of IL-6 accumulation. Moreover, the net IL-6 release from the exercising leg during 1 min at 5 h of exercise was approximately half of the IL-6 content in the blood. Indeed, the turnover rate of IL-6 in the human body must be very high when exercising and can be estimated to be 16 ng min−1 (9.07-23 ng min−1) simply by subtracting the amount accumulated in the last 2 h of exercise from the net IL-6 production, assuming that the active muscle is the only source of IL-6 production in the body during exercise.
Previous exercise studies on cytokines have examined eccentric exercise (Rohde et al. 1997; Hellsten et al. 1997; Bruunsgaard et al. 1997), combined concentric and eccentric exercise (Ostrowski et al. 1998a,b, 1999) or pure concentric exercise (Ullum et al. 1994; Bruunsgaard et al. 1997). In general, eccentric exercise has provoked higher plasma IL-6 concentrations than concentric exercise (Bruunsgaard et al. 1997; Utter et al. 1999). This difference has been attributed to eccentric exercise-induced muscle damage.
In the present study, we aimed to study the effect of muscle contraction on the production of IL-6 and exclude the possible influence of the eccentric exercise-induced muscle damage by using a concentric exercise model. One-legged dynamic knee extensor exercise represents a pure concentric exercise model where high force was produced per unit muscle mass engaged in exercise, with the advantage of using the other leg as control (Andersen et al. 1985; Richardson & Saltin, 1998). Thus, in the light of the present results, there is the possibility that one stimulus for IL-6 production by skeletal muscle is the force of the contraction. The amount of IL-6 produced by the active muscle is impressive, not only because of the small muscle mass that is active, but also because the workload, in relative terms, was as low as 40% of Wmax,ke. It is not possible to transfer these high production values to models where a large fraction of muscle mass is engaged in the concentric exercise. This is because when the exercise is confined to a relatively small muscle mass, the weight-specific power output is higher than in running or bicycling (Blomstrand et al. 1997).
It is a most remarkable finding that the knee extensors of the leg are able to produce an increase in plasma IL-6 concentration to reach a level comparable to that obtained during severe infections (Bruunsgaard et al. 1999). In infectious diseases, the source of cytokine production is the monocytes (Hack et al. 1997). It remains to be determined which cells in the contracting muscles are the source of IL-6 production. The time course for monocyte infiltration into active muscle is much longer than that for the release of IL-6 by contracting skeletal muscles (Smith, 1991). Furthermore, there is no relationship between the degree of muscle damage and monocyte infiltration on the one hand and the magnitude of eccentric exercise-related IL-6 production on the other (Bruunsgaard et al. 1997). There is, however, no question that the IL-6 is produced in the contracting skeletal muscle. We have reported earlier that IL-6 mRNA is present in human skeletal muscle after strenuous exercise (Ostrowski et al. 1998b) as well as in rat muscle after electrically stimulated concentric or eccentric contractions (Jonsdottir et al. 2000). In addition, IL-6 mRNA was not demonstrated in blood mononuclear cells, either before or after exercise (Ostrowski et al. 1998b). Moreover, it has been reported that regenerating mice myofibres are able to produce IL-6 (Kurek et al. 1996). In a recent report, it was shown that myoblasts produce IL-6 in response to inflammatory stimuli, and it has also been suggested that muscle cells are able to produce IL-6 in response to muscle injury (Gallucci et al. 1998). Hence, contracting muscle cells are likely to be one source of IL-6 production.
In sepsis, the main role of IL-6 is to stimulate the liver to produce acute phase proteins, such as C reactive protein (Hack et al. 1997). The exercise-induced elevation in IL-6 results in only a minor effect on the liver production of acute phase proteins (Pedersen & Hoffman-Goetz, 2000). It is striking that the exercise-induced increase in IL-6 appears to be a close function of exercise duration. IL-6 has been shown to markedly inhibit insulin-stimulated increases in glycogen deposition in rat hepatocyte cultures (Kanemaki et al. 1998). Furthermore, IL-6 was shown to inhibit glycogen synthase activity and accelerate glycogen phosphorylase activity (Kanemaki et al. 1998). Moreover, it has been demonstrated that injection of recombinant human IL-6 (rhIL-6) into humans increases the fasting blood glucose concentration in a dose-dependent manner (Tsigos et al. 1997).
Another study, also including humans, showed increased hepatic glucose output in response to injection of rhIL-6, concomitantly with a higher glucose metabolism (Stouthard et al. 1995). It has also been shown that consuming carbohydrate during exercise diminishes the exercise-induced increase in IL-6 (Nehlsen-Cannarella et al. 1997; Nieman et al. 1998).
Therefore, the possibility exists that IL-6 produced by contracting skeletal muscles directly or indirectly mediates the hepatic glucose output necessary to maintain the blood glucose level as the usage of blood glucose by skeletal muscles is markedly enhanced in prolonged exercise. We therefore propose that IL-6 is produced by the active skeletal muscle and exerts its effect in a hormone-like manner.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2270169
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Interleukin-6 Is Crucial for Recall of Influenza-Specific Memory CD4+ T Cells
Maria Paula Longhi#, Kate Wright#, Sarah N. Lauder, Mari A. Nowell, Gareth W. Jones, Andrew J. Godkin, Simon A. Jones, Awen M. Gallimore*
Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Heath Park, Cardiff, United Kingdom
Abstract
Currently, our understanding of mechanisms underlying cell-mediated immunity and particularly of mechanisms that promote robust T cell memory to respiratory viruses is incomplete. Interleukin (IL)-6 has recently re-emerged as an important regulator of T cell proliferation and survival. Since IL-6 is abundant following infection with influenza virus, we analyzed virus-specific T cell activity in both wild type and IL-6 deficient mice. Studies outlined herein highlight a novel role for IL-6 in the development of T cell memory to influenza virus. Specifically, we find that CD4+ but not CD8+ T cell memory is critically dependent upon IL-6. This effect of IL-6 includes its ability to suppress CD4+CD25+ regulatory T cells (Treg). We demonstrate that influenza-induced IL-6 limits the activity of virus-specific Tregs, thereby facilitating the activity of virus-specific memory CD4+ T cells. These experiments reveal a critical role for IL-6 in ensuring, within the timeframe of an acute infection with a cytopathic virus, that antigen-specific Tregs have no opportunity to down-modulate the immune response, thereby favoring pathogen clearance and survival of the host.
Author Summary
Influenza virus poses a serious global health threat, particularly in light of newly emerging strains such as the avian virus H5N1. The generation of cell-mediated vaccines against influenza virus requires an understanding of mechanisms underlying effective virus-specific T cell memory. This study explored the impact of a cytokine, interleukin-6 (IL-6), on generation of effective influenza-specific T cell memory. This cytokine was considered important based on previous studies revealing its role in promoting survival and activity of conventional T cells whilst inhibiting the activity of T cells involved in dampening down immunity (regulatory T cells). We found that the activity of a subset of influenza-specific memory T cells (CD4+ T cells) was diminished in the absence of IL-6 due to the inhibitory effects of regulatory T cells?an effect that compromised protective anti-viral immunity.
Since a robust CD4+ T cell response is likely to be central to the success of a vaccine against influenza virus, these findings highlight the importance of IL-6 in promoting effective cell-mediated immune responses, thereby facilitating successful virus clearance.
(snipped after long article)
last sentence of discussion.....
The results of this study imply that co-administration of IL-6 with an anti-influenza virus vaccine will promote development of protective immunity through optimal induction of a virus-specific memory CD4+ T cell response.
http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000006
Adam Steensberg,*? Gerrit van Hall,* Takuya Osada,* Massimo Sacchetti,* Bengt Saltin,* and Bente Klarlund Pedersen*?
*The Copenhagen Muscle Research Centre, University of Copenhagen, Copenhagen, Denmark
?The Department of Infectious Diseases, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
Corresponding author B. Klarlund Pedersen: The Department of Infectious Diseases and The Copenhagen Muscle Research Centre, Rigshospitalet 7652, Blegdamsvej 9, DK-2100 Copenhagen N, Denmark. Email:bkp@rh.dkReceived July 31, 2000; Accepted September 21, 2000.
Abstract
1.Plasma interleukin (IL)-6 concentration is increased with exercise and it has been demonstrated that contracting muscles can produce IL- The question addressed in the present study was whether the IL-6 production by contracting skeletal muscle is of such a magnitude that it can account for the IL-6 accumulating in the blood.
2.This was studied in six healthy males, who performed one-legged dynamic knee extensor exercise for 5 h at 25 W, which represented 40% of peak power output (Wmax). Arterial-femoral venous (a-fv) differences over the exercising and the resting leg were obtained before and every hour during the exercise. Leg blood flow was measured in parallel by the ultrasound Doppler technique. IL-6 was measured by enzyme-linked immunosorbent assay (ELISA).
3.Arterial plasma concentrations for IL-6 increased 19-fold compared to rest. The a-fv difference for IL-6 over the exercising leg followed the same pattern as did the net IL-6 release. Over the resting leg, there was no significant a-fv difference or net IL-6 release. The work was produced by 2.5 kg of active muscle, which means that during the last 2 h of exercise, the median IL-6 production was 6.8 ng min−1 (kg active muscle)−1 (range, 3.96-9.69 ng min−1 kg−1).
4.The net IL-6 release from the muscle over the last 2 h of exercise was 17-fold higher than the elevation in arterial IL-6 concentration and at 5 h of exercise the net release during 1 min was half of the IL-6 content in the plasma. This indicates a very high turnover of IL-6 during muscular exercise. We suggest that IL-6 produced by skeletal contracting muscle contributes to the maintenance of glucose homeostasis during prolonged exercise.
(snip)
DISCUSSION
The present study demonstrates that during exercise the net skeletal muscle IL-6 production increases strikingly and can account for the exercise-related high plasma IL-6 concentration. It is noteworthy that the large elevation in IL-6 was the result of exercise performed by only 2.5 kg of muscle, which during the last 2 h of exercise produced 6.8 ng IL-6 min−1 (kg muscle)−1 (3.96-9.69 ng min−1 kg−1).
When comparing the release of IL-6 from the contracting muscle with the amount accumulated in the body, it is quite apparent that the release markedly surpassed the rate of accumulation. The increase in arterial plasma IL-6 concentration during the last 2 h of exercise was 10.04 ng l−1 (8.30-12.00 ng l−1). Assuming that the IL-6 produced is diluted in the extracellular space (12 l), the total amount of IL-6 accumulated during the last 2 h of exercise was about 120.48 ng (99.60-144.08 ng) or 1.00 ng min−1 (0.83-1.20 ng min−1). This implies that the net release of IL-6 from the active leg was ≈17-fold higher than the rate of IL-6 accumulation. Moreover, the net IL-6 release from the exercising leg during 1 min at 5 h of exercise was approximately half of the IL-6 content in the blood. Indeed, the turnover rate of IL-6 in the human body must be very high when exercising and can be estimated to be 16 ng min−1 (9.07-23 ng min−1) simply by subtracting the amount accumulated in the last 2 h of exercise from the net IL-6 production, assuming that the active muscle is the only source of IL-6 production in the body during exercise.
Previous exercise studies on cytokines have examined eccentric exercise (Rohde et al. 1997; Hellsten et al. 1997; Bruunsgaard et al. 1997), combined concentric and eccentric exercise (Ostrowski et al. 1998a,b, 1999) or pure concentric exercise (Ullum et al. 1994; Bruunsgaard et al. 1997). In general, eccentric exercise has provoked higher plasma IL-6 concentrations than concentric exercise (Bruunsgaard et al. 1997; Utter et al. 1999). This difference has been attributed to eccentric exercise-induced muscle damage.
In the present study, we aimed to study the effect of muscle contraction on the production of IL-6 and exclude the possible influence of the eccentric exercise-induced muscle damage by using a concentric exercise model. One-legged dynamic knee extensor exercise represents a pure concentric exercise model where high force was produced per unit muscle mass engaged in exercise, with the advantage of using the other leg as control (Andersen et al. 1985; Richardson & Saltin, 1998). Thus, in the light of the present results, there is the possibility that one stimulus for IL-6 production by skeletal muscle is the force of the contraction. The amount of IL-6 produced by the active muscle is impressive, not only because of the small muscle mass that is active, but also because the workload, in relative terms, was as low as 40% of Wmax,ke. It is not possible to transfer these high production values to models where a large fraction of muscle mass is engaged in the concentric exercise. This is because when the exercise is confined to a relatively small muscle mass, the weight-specific power output is higher than in running or bicycling (Blomstrand et al. 1997).
It is a most remarkable finding that the knee extensors of the leg are able to produce an increase in plasma IL-6 concentration to reach a level comparable to that obtained during severe infections (Bruunsgaard et al. 1999). In infectious diseases, the source of cytokine production is the monocytes (Hack et al. 1997). It remains to be determined which cells in the contracting muscles are the source of IL-6 production. The time course for monocyte infiltration into active muscle is much longer than that for the release of IL-6 by contracting skeletal muscles (Smith, 1991). Furthermore, there is no relationship between the degree of muscle damage and monocyte infiltration on the one hand and the magnitude of eccentric exercise-related IL-6 production on the other (Bruunsgaard et al. 1997). There is, however, no question that the IL-6 is produced in the contracting skeletal muscle. We have reported earlier that IL-6 mRNA is present in human skeletal muscle after strenuous exercise (Ostrowski et al. 1998b) as well as in rat muscle after electrically stimulated concentric or eccentric contractions (Jonsdottir et al. 2000). In addition, IL-6 mRNA was not demonstrated in blood mononuclear cells, either before or after exercise (Ostrowski et al. 1998b). Moreover, it has been reported that regenerating mice myofibres are able to produce IL-6 (Kurek et al. 1996). In a recent report, it was shown that myoblasts produce IL-6 in response to inflammatory stimuli, and it has also been suggested that muscle cells are able to produce IL-6 in response to muscle injury (Gallucci et al. 1998). Hence, contracting muscle cells are likely to be one source of IL-6 production.
In sepsis, the main role of IL-6 is to stimulate the liver to produce acute phase proteins, such as C reactive protein (Hack et al. 1997). The exercise-induced elevation in IL-6 results in only a minor effect on the liver production of acute phase proteins (Pedersen & Hoffman-Goetz, 2000). It is striking that the exercise-induced increase in IL-6 appears to be a close function of exercise duration. IL-6 has been shown to markedly inhibit insulin-stimulated increases in glycogen deposition in rat hepatocyte cultures (Kanemaki et al. 1998). Furthermore, IL-6 was shown to inhibit glycogen synthase activity and accelerate glycogen phosphorylase activity (Kanemaki et al. 1998). Moreover, it has been demonstrated that injection of recombinant human IL-6 (rhIL-6) into humans increases the fasting blood glucose concentration in a dose-dependent manner (Tsigos et al. 1997).
Another study, also including humans, showed increased hepatic glucose output in response to injection of rhIL-6, concomitantly with a higher glucose metabolism (Stouthard et al. 1995). It has also been shown that consuming carbohydrate during exercise diminishes the exercise-induced increase in IL-6 (Nehlsen-Cannarella et al. 1997; Nieman et al. 1998).
Therefore, the possibility exists that IL-6 produced by contracting skeletal muscles directly or indirectly mediates the hepatic glucose output necessary to maintain the blood glucose level as the usage of blood glucose by skeletal muscles is markedly enhanced in prolonged exercise. We therefore propose that IL-6 is produced by the active skeletal muscle and exerts its effect in a hormone-like manner.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2270169
----------------------------------------------------------------------------------
Interleukin-6 Is Crucial for Recall of Influenza-Specific Memory CD4+ T Cells
Maria Paula Longhi#, Kate Wright#, Sarah N. Lauder, Mari A. Nowell, Gareth W. Jones, Andrew J. Godkin, Simon A. Jones, Awen M. Gallimore*
Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Heath Park, Cardiff, United Kingdom
Abstract
Currently, our understanding of mechanisms underlying cell-mediated immunity and particularly of mechanisms that promote robust T cell memory to respiratory viruses is incomplete. Interleukin (IL)-6 has recently re-emerged as an important regulator of T cell proliferation and survival. Since IL-6 is abundant following infection with influenza virus, we analyzed virus-specific T cell activity in both wild type and IL-6 deficient mice. Studies outlined herein highlight a novel role for IL-6 in the development of T cell memory to influenza virus. Specifically, we find that CD4+ but not CD8+ T cell memory is critically dependent upon IL-6. This effect of IL-6 includes its ability to suppress CD4+CD25+ regulatory T cells (Treg). We demonstrate that influenza-induced IL-6 limits the activity of virus-specific Tregs, thereby facilitating the activity of virus-specific memory CD4+ T cells. These experiments reveal a critical role for IL-6 in ensuring, within the timeframe of an acute infection with a cytopathic virus, that antigen-specific Tregs have no opportunity to down-modulate the immune response, thereby favoring pathogen clearance and survival of the host.
Author Summary
Influenza virus poses a serious global health threat, particularly in light of newly emerging strains such as the avian virus H5N1. The generation of cell-mediated vaccines against influenza virus requires an understanding of mechanisms underlying effective virus-specific T cell memory. This study explored the impact of a cytokine, interleukin-6 (IL-6), on generation of effective influenza-specific T cell memory. This cytokine was considered important based on previous studies revealing its role in promoting survival and activity of conventional T cells whilst inhibiting the activity of T cells involved in dampening down immunity (regulatory T cells). We found that the activity of a subset of influenza-specific memory T cells (CD4+ T cells) was diminished in the absence of IL-6 due to the inhibitory effects of regulatory T cells?an effect that compromised protective anti-viral immunity.
Since a robust CD4+ T cell response is likely to be central to the success of a vaccine against influenza virus, these findings highlight the importance of IL-6 in promoting effective cell-mediated immune responses, thereby facilitating successful virus clearance.
(snipped after long article)
last sentence of discussion.....
The results of this study imply that co-administration of IL-6 with an anti-influenza virus vaccine will promote development of protective immunity through optimal induction of a virus-specific memory CD4+ T cell response.
http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000006