S Tanabe, Z Lu, Y Luo, E J Quackenbush, M A Berman, L A Collins-Racie, S Mi, C Reilly, D Lo, K A Jacobs, M E Dorf

Thymus-derived chemotactic agent 4 (TCA4), a new member of the beta-chemokine family, was cloned from a mouse thymic cDNA library. High levels of TCA4 mRNA are expressed in thymus; lower levels of message are found in spleen, heart, and kidney. Anti-TCA4 antibodies were used to localize sites of TCA4 expression within lymphoid tissues. In the thymus, UEA-1+ medullary epithelial cells, some endothelial cells, and additional undefined stromal elements were stained with anti-TCA4. TCA4 was also expressed as a meshlike network in splenic white pulp and in the medullary region of the lymph nodes. In addition, some lymph node and splenic blood vessels stained with anti-TCA4 antibodies. Rel B NFkappaB-deficient mice lack a transcription factor required for the generation of dendritic cells and the development of an organized thymic medulla. Rel B-deficient animals express very low levels of TCA4 in the thymus and little or no TCA4 in the periphery. At subnanomolar concentrations, TCA4 is a chemoattractant of mature T cells; the potential role of this novel chemokine in facilitating normal lymphocyte traffic is discussed. TCA4 is also a chemoattractant of cultured mesangial cells. Neutralizing anti-TCA4 mAb was used to demonstrate the specificity of TCA4-mediated cell migration. Finally, competitive binding studies with a SV40-transformed mouse mesangial cell line demonstrated that other murine beta-chemokines (monocyte chemotactic protein-1, macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta, and thymus-derived chemotactic agent 3) do not compete for TCA4 binding.