Impaired T-dependent immune response in L-dopa treated BALB/c mice

Various neurotransmitters and neuropharmacological agents can affect lymphocyte responses. The purpose of the present study was to investigate the potential immunological effects of L-dihydroxyphenylalanine (L-dopa), the direct precursor of dopamine, by examining the influence of the in vivo administration of the drug on different functional and phenotypic parameters in BALB/c mice. L-dopa at the dose of 100 mg/kg/day altered T-dependent immune responses. The antibody response to sheep red blood cells (SRBC) was abolished by the drug. The delayed-type hypersensitivity reaction to SRBC was also depressed. Lymphocyte proliferation and generation of cytotoxic T cells in response to allogeneic stimulator cells in vitro were decreased by L-dopa treatment. These suppressive effects were correlated with a decrease in spleen T cells number. However, the proliferative response of spleen cells to concanavalin A was greatly enhanced by the L-dopa treatment. Conversely, there was no evidence for alteration of T-independent immune responses by L-dopa. Hence, the antibody response to TNP-Ficoll, and the proliferation of B spleen cells induced by E. coli lipopolysaccharide were unchanged. Altogether, these results showed that L-dopa which is converted to dopamine in the organism, could selectively affect T-dependent immune responses. The integration of these findings in the immune-neuroendocrine interactions, and the possible sites and mechanisms of action are discussed.