A subset of dendritic cells express joining chain (J-chain) protein

Joining chain (J-chain) is well known as an integrated component of dimeric immunoglobulin A (IgA) and pentameric IgM. We show here that the J-chain protein is also expressed in a subset of CD11c(+) dendritic cells (DC) in C57BL/6 mice. J-chain knockout mice (J(-/-) mice) had a reduced fraction of CD4(-)/CD8 alpha(+) and mPDCA-1(+) DC in the spleen. J(-/-) mice also had reduced levels of RNA for the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) in the spleen. Furthermore, in lymph nodes from C57BL/6 mice the majority of J-chain-expressing CD11c(+) cells also expressed IDO, while the number of IDO-expressing cells in lymph nodes and the amount of IDO protein in splenic CD11c(+) cells were reduced in J(-/-) mice. Also, J(-/-) mice had a lower ratio of kynurenine/tryptophan in serum compared to C57BL/6 mice, indicating a lower overall IDO activity in J(-/-) mice. We also show that J(-/-) mice are less susceptible to tolerance induction than C57BL/6 mice. In conclusion, our data show that J-chain protein is expressed outside the B-cell compartment in a subset of immunoregulatory DC that are compromised in animals that cannot express J-chain.