Supplemental arginine and ornithine do not affect splenocyte proliferation in surgically treated rats

Arginine and immunity: a unique perspective

Arginine functions in the body as a free amino acid, a component of most proteins, and the substrate for several non-protein, nitrogen-containing compounds, many of which function in immunity. Although arginine is synthesized in the body, it is not made in sufficient quantities to support growth or meet metabolic requirements during periods of stress. Based on the biochemical and physiological role of arginine in maintaining health and immunity, arginine is being added at pharmacologic concentrations to enteral formulas to boost immune function. Unfortunately, animal and human studies that investigate enteral arginine supplementation as the single variable do not show clear immunologic benefit. The inconsistent effects of arginine supplementation on immune function are due to numerous factors, such as the amount and timing of arginine supplementation, the animal species or strain of species, and the experimental model. Systematic study is required to determine whether a basal dietary intake of arginine is required to maintain immune function during health and how much arginine is required to meet metabolic requirements during periods of growth or stress.

Effects of L-arginine supplementation on human lymphocyte proliferation in response to nonspecific and alloantigenic stimulation

BACKGROUND

L-Arginine has been described as a potential immunostimulant in vitro and in vivo. Excessive arginine, however, may be counterproductive. Data support the concept of minimal arginine requirements for normal lymphocyte proliferation, but the results of supplementation with pharmacologic doses of arginine have been contradictory. We hypothesized that excessive arginine supplementation might result in a blunting of normal immune responses of human lymphocytes in vitro.

MATERIALS AND METHODS

Peripheral blood mononuclear and T-cells were isolated from normal human donors. Cells were cultured in complete media with various concentrations of L-arginine, L-ornithine, and glycine. Lymphocytes were then stimulated with PHA or alloantigens, and proliferation was determined by measuring [3H]thymidine incorporation.

RESULTS

Lymphocyte proliferation was inhibited by L-arginine at pharmacologic doses. The effects were completely reversible. This inhibition could not be prevented by lymphocyte stimulation with IL-2. Lymphocyte proliferation was more sensitive to inhibition by lower doses of arginine when alloantigens from irradiated fresh tumor cells or allogeneic lymphocytes were the stimuli. Finally, lymphocytes showed variable sensitivity to inhibition of proliferation in response to mitogen when treated with L-ornithine (little to no effect) or L-arginine (consistent inhibition at high doses). Pharmacologic doses of L-arginine result in reversible inhibition of normal lymphocyte proliferation in response to both mitogen and alloantigen. This inhibition could not be blocked by interleukin-2.

CONCLUSIONS

We conclude that caution should be exercised when recommending aggressive L-arginine supplementation as a possible method to reverse clinical immunosuppression caused by cancer, malnutrition, or trauma.