Cytokines

Macrophage migration inhibitory factor (MIF) plays a pivotal role in immunity against Salmonella typhimurium.Koebernick, H. et al. Proc. Natl Acad. Sci. USA 99, 13681–13686 (2002)

Although the cytokine macrophage migration inhibitory factor (MIF) has many biological functions, its role in bacterial infections is not understood. Here, Koebernick et al. investigated the response of Mif−/− mice to Salmonella typhimurium. Mif−/− mice were unable to control this bacterial infection, and they had an impaired T helper 1 (TH1) response, as indicated by the reduced production of interleukin-12, interferon-γ and tumour-necrosis factor. In addition, increased levels of nitric oxide and corticosteroids were seen. Therefore, MIF promotes TH1 responses and reduces immunosuppressive stress responses.

Thymic development

Stromal cells provide the matrix for migration of early lymphoid progenitors through the thymic cortex.Prockop, S. et al. J. Immunol. 169, 4354–4361 (2002)

As thymocytes develop into mature T cells in the thymus, they migrate outwards from the cortex towards the thymic capsule. What controls this directional migration? Adhesion receptors on the migrating lymphoid cells are required, as well as a stable matrix of their ligands. This study investigates the nature of this matrix and indicates that it is cellular rather than extracellular, and includes cytokeratin-positive cortical stromal cells that express the α4-integrin ligand vascular cell adhesion molecule 1, which are crucial for the control of precursor migration.

B-Cell development

B cells develop in the zebrafish pancreas.Danilova, N. & Steiner, L. A. Proc. Natl Acad. Sci. USA 99, 13711–13716 (2002)

In bony fish, T-cell development takes place in the thymus, whereas the pronephros (or head kidney) is thought to be the main site of B-cell development. However, expression of recombination-activating gene 1 (Rag1) and Rag2 is not detected in the zebrafish pronephros until three weeks of life. By contrast, Rag1/2 expression can be detected in the thymus by day 4. So, is early B-cell development in zebrafish delayed relative to T-cell development, or does it take place at a distinct anatomical site? This study shows that rearrangements of the genes that encode Igμ can be detected in DNA extracted from whole zebrafish as early as day 4 and that Rag1 is expressed in the pancreas by day 4. Igμ is also expressed in the pancreas from day 10, which confirms that the pancreas is an organ for B-cell development in the zebrafish.