For the neurotrophin BDNF several splice variants were recently described. We analyzed the expression of mBDNF mRNA splice variants in cells of the immune system in comparison to the central nervous system (CNS). Whereas all splice variants are expressed in the CNS, only mBDNF 3 mRNA could be detected in primary and secondary lymphoid organs as well as in purified T cells and macrophages. After activation, only mBDNF 3 mRNA expression was upregulated in T cells without the additional appearance of other mBDNF splice variants. Therefore, mBDNF mRNA is differentially regulated in the CNS and the immune system opening the possibility of specific manipulation of mBDNF expression in immune cells without globally affecting mBDNF in the CNS.