Expression of tyrosine hydroxylase in lymphocytes and effect of endogenous catecholamines on lymphocyte function

To comprehend the changes and significance of the endogenous catecholamines in the immune system, we explored the synthesis of catecholamines by lymphocytes in various lymphoid organs and in different activated states, and the effect of the endogenous catecholamines synthesized by lymphocytes on the function of the lymphocytes themselves.

Immunohistochemistry for lymphoid organs (mesenteric lymph nodes, spleen and thymus) and lymphocytes was used to observe their expression of tyrosine hydroxylase (TH), an initial rate-limiting enzyme of the catecholamine synthesis. The contents of catecholamines, including norepinephrine (NE), dopamine (DA) and epinephrine (E), in lymphocytes were tested by means of high-performance liquid chromatography with electrochemical detection. Western blot was used to examine the character and relative quantity of TH-stained protein in lymphocytes, lymph nodes and adrenal medullary tissue. The effect of alpha-methyl-P-tyrosine (alpha-MT), an inhibitor of TH activity, on concanavalin A (Con A)-induced interleukin-2 (IL-2) production was determined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay.

TH-positive cells were found in the three examined lymphoid organs, but the lymph nodes had the highest and the thymus had the lowest density. Both TH expression and the contents of NE, DA and E in the Con A-activated lymphocytes were markedly increased in comparison with those in the nonactivated lymphocytes. A band with TH immunoreactivity was seen in the extracts from either Con A-activated lymphocytes or nonactivated cells and the molecular weight of the protein was 59.4 +/- 0.3 kD. However, the relative quantity of the protein was notably higher in the activated lymphocytes than in the nonactivated cells. As a positive control, a similar band of TH immunoreactivity in the adrenal medullary tissue was also obtained. Alpha-MT at the doses of 10(-11), 10(-10) and 10(-9) M was found to significantly facilitate the Con A-induced IL-2 production.

These results suggest that lymphocytes can synthesize catecholamines and their synthesis levels may increase in the activated state, and that endogenous catecholamines synthesized by the lymphocytes can regulate the function of the lymphocytes themselves.