Exercise + CR for immune system

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Hi All,

Exercise plus CR seems to be important for the immune system.

I was interesting in reading:

" ... sedentary-energy–restricted

rats (SER), which received 50% of the mean amount of chow

consumed by SF (9); " ,

yet 50% CR gives about 50% less body weight.

The involvement of glutamine in blood and _expression of its

synthesis mRNA opened my eyes.

The paper has good introduction and discussion sections,

and, therefore, I will leave the pdf excerpt below do the speaking.

The pdf is available.

Med Sci Sports Exerc. 2004 Dec;36(12):2059-2064.

Exercise Restores Immune Cell Function in Energy-Restricted Rats.

... Forty male Wistar rats were randomly assigned to the following

groups:

sedentary animals fed ad libitum (SF, N = 10) or submitted to energy

restriction

(SER, N = 10, receiving 50% of the mean amount of chow consumed by

SF); and

trained animals fed ad libitum (TF, N = 10) or submitted to energy

restriction

(TER, N = 10), who exercised on a treadmill (at 60-65% & OV0312;O2max)

5 d.wk for

10 wk, after 30 d under the restriction protocol. ... were measured

in all groups, 24 h

after the last exercise session. Two-way ANOVA and Tukey's posttest

were

employed for the statistical analysis. RESULTS: Training induced an

increase in

the proliferative response and in the production of gamma-interferon

and

interleukin-1 (P < 0.05) in cells from the spleen and lymph nodes of

SER, in

which these parameters were diminished when compared with SF (P <

0.05). SER

spleen and lymph node cells produced more TNF (26 and 42%,

respectively) and

IL-2 (49 and 42%, respectively) than SF. The Th1-like diversion of

the immune

response observed in SER persisted after training. Partial recovery

of the

decreased SER plasma glutamine concentration and muscle glutamine

synthase mRNA

was observed. CONCLUSIONS: Training induced the recovery of the

proliferative

capacity of lymphocytes from SER, probably due to the partial

restoration of

plasma glutamine levels, but did not interfere with the diversion

towards a

Th1-type immune response induced by food restriction.

PMID: 15570140 [PubMed - as supplied by publisher]

Exercise modulates both the innate and the acquired

branches of the immune system. The direction and

magnitude of the changes, however, are influenced

by numerous factors (such as the type, duration, and inten-sity

of exercise), as well as the conditioning level and age of

the subject (4). Because of the number of factors influencing

the immune system during exercise, a multitude of findings,

from immunodepression to immunostimulation, has been

reported.

During exercise, there is recruitment of natural killer cells

(NK) and B and T lymphocytes to the blood, leading to an

increased total lymphocyte count (4). After a prolonged and

intense bout of exercise, however, the number of NK and

lymphocytes in peripheral blood is reduced, as is the func-tion

of NK and B lymphocytes (4). The response of lym-phocytes

to mitogens after exercise is still subject to con-troversy,

because both decreases and increases in this

parameter are reported in the literature (23). Despite differ-ent

findings across studies, it is clear that exercise modifies

the cellular and humoral branches of the immune system,

and that regular physical activity at light to moderate levels

can increase the host's resistance to disease, whereas heavy

exertion enhances the risk of illness (23). The mechanism by

which endurance exercise induces changes in leukocyte

function and number is complex and includes immune and

neuroendocrine signals, with an augmented release of var-ious

hormones, peptides, and cytokines (23,29), and

changes in plasma glutamine levels (21).

The fact that moderate regular activity contributes to

improved immune response has led the medical community

to adopt it as a complementary therapeutic strategy for the

management of various conditions, including cancer ca-chexia

and AIDS (1,12). Undernourishment is still a notice-able

cause of impaired immunocompetence, and has been

shown to be an important causal factor in the increased

susceptibility to infection in normal subjects and hospital-ized

patients (14). Indeed, the lack of appropriate food

intake is a decisive factor in predisposing to infectious

diseases and death (24) in the low-income population. In

such cases, changes in the immune system could be consid-ered

as part of a process of closing down functions, which

can be best sacrificed in the short term to ensure long-term

survival (24).

Undernutrition has been acknowledged to depress both

cell-mediated and humoral immunity, resulting in thymus,

spleen, and lymph node atrophy (2,31), and to significantly

impair macrophage activation (26). It also induces a de-crease

in the absolute number of T cells (6) and lower

hormone production by the thymus (5), as well as dimin-ished

delayed-type hypersensitivity (20). Energy restriction

is also known to impair the development of cytotoxic T cells

(17). The changes observed depend, however, upon the

severity and time of exposure to energy restriction, as well

as on the type of dietary protein consumed (24,25).

Considering that moderate-intensity exercise has been

linked to immune stimulation, we have sought to address the

effect of endurance training upon the immune cells of rats

submitted to energy restriction.

METHODS

... sedentary-energy–restricted rats (SER), which received

50% of the mean amount of chow consumed by SF (9);

animals submitted to 10 wk of endurance training, 30 d after

the beginning of the energy restriction (TER) program; and

trained rats fed ad libitum (TF). After the 14 wk of the

experiment, animals from the SER group presented reduced

plasma albumin concentration (from 3.98 +/- 0.29 g·dL-1 in

SF to 2.14 +/- 0.27 g·dL-1 in the SER group), as well as a

pronounced reduction in the number of splenocytes; all of

these symptoms are considered markers of undernutrition

(9). To further evaluate the influence of energy restriction

upon the immune system, we examined the proliferative

capacity of lymphocytes obtained from the mesenteric

lymph nodes and the spleen, as well as the ability of these

cells to produce cytokines after 48 h in culture.

.... Because glucose and glutamine are impor-tant

substrates for these cells (22)

.... glutamine synthase mRNA in the skeletal muscle (oxidative

fiber-rich red portion of the gastrocnemius).

Animals. Forty male Wistar rats of equivalent age, each

weighing around 50 g on the first day of the experiment,

.... The following groups were

studied: sedentary rats fed ad libitum (SF, N = 10); seden-tary

rats submitted to energy restriction (SER, N = 10);

trained rats fed ad libitum (TF, N = 10); and energy-restricted

trained rats (TER, N = 10). ...

Training protocol. The rats were submitted, as de-scribed

by Meneguello and colleagues (19), to a pretraining

period of 1 wk, during which they ran progressively from 15

to 60 min, at 10 m·min-1 . During the training period of 10

wk (training 5 d·wk-1 ), the animals exercised on a motor-ized

treadmill (Enlaup, Sa˜o o, Brazil) at 24°C and 80%

humidity in the dark. Running velocity increased to 22

m·min-1 in the last 2 wk, and the intensity was maintained

between 60 and 65% V & #729; O 2max , as determined periodically in

an Oxymax Columbus System (Columbus Instruments, Co-lumbus,

OH). ... In the 10th week, all groups performed an

incremental test until exhaustion. Because the rats adapted

readily to the treadmill, and the exercise sessions were

performed during the period of activity of the animals, no

reinforcement was required. The training sessions were per-formed

at the same time each day to avoid circadian

interferences.

.... RESULTS

Characterization of the state of undernourish-ment.

Rats submitted to energy restriction showed reduced

body weight (49%, Fig. 1) in comparison with controls.

These animals also presented noticeable changes in thymus

structure under light microscopy (not shown), with remark-able

atrophy, as the parenchyma was partially replaced by

fatty and fibrous tissue. Energy restriction also induced loss

of cortex/medulla differentiation in the organ.

The influence of energy restriction upon the immune

system was addressed by evaluating the proliferative capac-ity

of lymphocytes obtained from the mesenteric lymph

nodes and the spleen, as well as the ability of these cells to

produce cytokines after 48 h in culture. Energy restriction

induced a reduction in the proliferative response of lympho-cytes

from both sources (48 and 59%, for lymph node and

spleen cells, respectively (Table 1)). This protocol also

provoked a marked reduction in the mitogenic response of

these cells to concanavalin A (decreasing 77 and 59% for

LFN and spleen lymphocytes, respectively (Table 1)) as

compared with control cells.

Splenocytes from SER animals produced less gamma-inter-feron

and interleukins 1, 4, and 10 after 48 h in culture

(decreasing 58, 49, 51, and 64%, respectively (Table 2)) in

comparison with C. The same pattern was observed in LFN:

reduction of 69, 61, 37, and 48% in gamma-interferon and inter-leukins

1, 4, and 10 production, respectively (Table 2). The

cells obtained from the spleen of SER, however, showed

increased interleukin- 2 production (19%, (Table 2)) in

relation to SF.

The animals submitted to energy restriction showed re-duced

plasma glutamine concentration (44%), but increased

concentration of glutamine synthase mRNA (3.7-fold),

compared with SF (Table 3).

Effect of training.

The moderate-intensity training pro-tocol

imposed upon the animals submitted to energy restric-tion

restored spleen and mesenteric lymph node cells pro-liferative

response, as shown in Table 1, as well as the

production of gamma-interferon and interleukin 1 (Table 2). Cells

obtained from the spleen of TER produced 26% more TNF

and 44% more IL-2 than those from SER (Table 2), but less

IL-4 (49%) and IL-10 (60%). Similarly, the cells from the

mesenteric lymph nodes from TER produced more IL-2

(42%) and less IL-4 (39%) and IL-10 (41%) than those

obtained from SER. Interestingly, skeletal muscle from SER

presented an increased _expression of glutaminase synthase

mRNA, concomitant with a reduction in plasma glutamine

concentration.

DISCUSSION

It is well known that undernutrition leads to immunosup-pression

(31). We have, therefore, sought to examine the

effects of moderate-intensity exercise training upon some of

the parameters of immune cell metabolism and function that

are modified in response to energy restriction. Energy re-striction

is also acknowledged to induce thymus atrophy,

with important changes in thymus structure and severe loss

of function, as the differences between the cortical and

medullar zone of the lobules are lost (2). Despite the

changes observed in the thymus, a moderate increase in

splenic T cells' responsiveness to polyclonal mitogens in-ducing

IL-2 production has been previously reported (31).

We also observed increased production of IL-2 after energy

restriction, not only by cells from the spleen, but also by

cultured cells obtained from the mesenteric lymph nodes

(LFN) (9). These results, however, are not a consensus, as

many other groups did not find changes in cytokine produc-tion

in undernourished animals (7). Our data also demon-strated

that the production of tumor necrosis factor was not

altered by energy restriction, whereas that of INF, IL-1,

IL-4, and IL-10 was reduced, indicating that this protocol

modified specific aspects of the immune response. In fact,

cytokines, which are signaling molecules of the immune

system, play an important role in controlling its homeosta-sis,

and may be divided into proinflammatory cytokines

(IL-1, IL-6, IL-8, and TNF-alpha) and T-helper type 1 (Th 1 )

cytokines, such as IL-2 and IFN-gamma, or still, T helper type 2

(Th 2 ) cytokines, IL-4, IL-10 (27). The balance of cytokines

modulates the profile (cellular or humoral) and intensity of

the response (27). Therefore, the changes in the profile of

cytokine production observed in our model lead to a diver-sion

toward a Th 1 -like response, with a decreased produc-tion

of specific antibodies and mucosal IgA levels (18).

The changes in cytokine production by cultured mono-nuclear

cells from the spleen and mesenteric lymph nodes

were accompanied by a reduction in the proliferative re-sponse

to concanavalin A, a mitogen for T-cells. Consider-ing

that IL-2 is a very important cytokine for the stimulation

of T-cell proliferation, and that its production is increased in

SER, the decrease observed in cell proliferation should be

related to an impairment in the function of antigen-present-ing

cells, as previously described by Zhang and Petro (31),

in a model of protein malnutrition.

Glutamine is an essential amino acid for immune cells,

including lymphocytes and antigen-presenting cells such as

B-lymphocytes and macrophages (10). We chose to inves-tigate

the effect of energy restriction upon the concentration

of this amino acid in the plasma. It has been previously

reported (15) that there is an increase of plasma glutamine

concentration in rats fasted for 48 h (15), paralleled by a

reduction in intestinal glutaminase activity and an increase

in liver net output of the amino acid (15). This change in

plasma glutamine concentration is fully abolished by a

chronic caloric restriction regimen (9). It is interesting to

note, however, that the _expression of glutamine synthase

mRNA was increased in the skeletal muscle of energy-restricted

rats. The enhancement in glutamine synthase ac-tivity

and _expression could be related to the lower plasma

glutamine concentration, as previously demonstrated by

Labow and colleagues (16), who showed a 3.5-fold increase

in the activity of this enzyme in skeletal muscle after glu-tamine

starvation. The increase in enzyme _expression was

not matched by changes in plasma glutamine concentration,

probably because of an increased demand for glutamine by

immune cells and possibly enterocytes, as well as by the

liver and kidney, which may use this amino acid for glu-coneogenesis

(3). Therefore, we can speculate that there is

an increased demand (similar to what occurs during glu-cocorticoid

treatment (3)) during energy restriction for glu-tamine,

which is greater than the individual's maximal syn-thesis

capacity, leading to a reduction in plasma

concentration (3).

The moderate-intensity training protocol adopted herein

restored the proliferative activity of cells obtained from the

spleen and mesenteric lymph nodes, as well as their ability

to respond to concanavalin A. It is interesting to note,

however, that training, although able to induce the recovery

of cell proliferative capacity, did not increase that response

in comparison with that observed for cells obtained from

control animals. In fact, the effect of exercise upon leuko-cyte

proliferation is known to vary according to the type,

duration, and intensity of the exercise, as described by Fry

and colleagues (11) and demonstrated by other research

groups (23).

The moderate exercise training protocol was not able to

reverse the energy-restriction–induced diversion of the im-mune

response towards a Th 1 type, as it provoked an in-crease

in IL-2 production and a decrease in IL-4 and IL-10

synthesis by cultured cells.

The training program induced a partial recovery of

plasma glutamine concentration. Cunha and colleagues (9)

demonstrated that the addition of glutamine to the culture

medium of lymphocytes obtained from undernourished rats

(who present decreased plasma concentration of the amino

acid) restored their ability to produce cytokines and to

proliferate in response to concanavalin A. Therefore, we can

speculate that the partial recovery of plasma glutamine

concentration induced by training could at least partly ex-plain

the recovery of immune function observed in our

study.

The alterations in glutamine flux, on the other hand, could

be related to changes in plasma corticosterone concentration

and glutamine synthase activity, as both glutamine and

glucocorticoids decrease glutamine synthase mRNA expres-sion

in the skeletal muscle (3).

Concluding remarks. Although previous work by our

group and others has shown disruption of splenocyte func-tion

caused by energy restriction, this is the first study, to

our knowledge, to address and characterize the effect of

undernutrition on lymphocytes obtained from the lymph

nodes. Chronic endurance exercise was able to reestablish

immune cell (both splenocytes and lymph node cells) func-tion

in energy-restricted rats, an effect that could be, at least

partially, associated with the observed increase in plasma

glutamine levels induced by training. The diversion towards

a Th 1 -type response caused by energy restriction was not

affected by training.

Taken together, our results demonstrate that the moder-ate-

intensity exercise training program was able to partially

revert the changes in immune cell function observed in rats

submitted to energy restriction, while reinforcing a diver-sion

of the immune response toward a Th 1 -type response.

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Cheers, Alan Pater