Zebrafish are an exciting model organism because of their readily manipulated genetics and transparent nature. Zon and colleagues report on pp. 1238–1246 that immune system development could be amenable to study in zebrafish. This 2-day-old embryo illustrates how one can monitor multilineage hematopoiesis in living zebrafish after transplantation of transgenic donor marrow carrying red (leukocytes; gata1dsRED) and green (erythrocytes; bactineGFP) fluorescent markers. Digital image by D. Travers.

The lack of visible pigment combines with defective cytotoxic T lymphocytes (CTLs) in a rare form of albinism called Hermansky-Pudlak Syndrome type 2. Griffiths and colleagues (p 1111; News and Views on p 1049) found a particular AP-3 mutant that both missorts tyrosinase in melanocytes and disables lytic granule transport to the immune synapse. Photomicrograph of CTL granules (green) and microtubules (red); clay sculpture by Lewis Long.

Chemoattractants recruit effector T cells (light pink/rose elements) to microvessels (red) in inflamed tissue. In three papers, leukotriene B4 (LTB4) is reported to be a potent nonchemokine tissue attractant for T cells. See articles by von Andrian and colleagues (pages 965-973), Ott et al. (pages 974-981) and Luster and colleagues (pages 982-990), and a News and Views by Schoenberger (page 937). Photo, von Andrian laboratory; art work, Lewis Long.

All T cells require the calcineurin-NFAT pathway for normal activation. McKeon and colleagues (pages 874–881) show that calcipressin prevents NFAT (red) movement to the nucleus. Lack of calcipressin dysregulates Fas ligand expression, to which T helper type 1 (TH1) cells are particularly sensitive, leaving calcipressin-deficient mice with crippled TH1 responses. See also the News and Views by Parry and June (page 821). Artwork is acrylic on paper by Lewis Long.

A thymus section in the style of Vincent Van Gogh (1853-1890). Fowlkes and colleagues show that by increasing the number of CD4+CD8+ thymocytes that cannot be selected in a given microenvironment, lineage commitment can be redirected. Confocal micrograph by Matilde Canelles; art by Lewis Long.

The control of DNA accessibility is a theme throughout our Focus on Chromatin Dynamics (pages 601–639; free online until the end of September 2003). Like the intricate braids of Leda as sketched by Leonardo da Vinci, chromatin has various states. Heterochromatin is as inaccessible as tightly coiled braids (1), loose curls (2) represent more accessible DNA, and untwined strands (3) resemble the opened templates necessary for replication or transcription into RNA (4). [Original image © Alinari Archives/CORBIS]

Lymphocyte development depends on appropriate expression of transcription activators and regulators, as illustrated by two reports in this issue. Wakabayashi et al. now report that Bcl11b-deficient mice had abnormal thymic development and Liu et al. find that Bcl11a mice have disrupted B and T cell maturation. Micrograph from Wakabayashi et al. and artwork by Lewis Long.

Death, symbolized by the autumn leaf, befalls tumor cells (star-shaped) that receive lytic granules (red in the original micrograph) from cytotoxic T lymphocytes. This month's Focus on Cell Death and Immunity comprises four reviews (starting on p. 399) and four more in Nature Reviews Immunology. All reviews and online features are available free to registered users through 1 July 2003. Original photo by Federico Gallo. Artwork by Lewis Long.

A pattern of Langerhans cells (green, bottom image) in the style of Andy Warhol (1928–1987). Microarray analysis led Zenke and colleagues to examine the role of Id2 in dendritic cell development. CD8α+ dendritic cells and Langerhans cells were missing in mice that lacked Id2, which may be induced by TGF-β to suppress B lineage genes. Artwork by Lewis Long.

A mouse Paneth cell (bottom image) in the abstract style of Swiss painter Paul Klee (1879-1940). Hooper et al. (page 270) report that angiogenin 4 is microbicidal and released from distinctive granules (red) in these cells at the base of the crypts of the small intestine, in response to indigenous gut bateria. Electron micrograph by T.S. Stappenbeck, rendering by Lewis Long.

Artist's rendition of lymphocytes in the small intestinal villi. In a murine model of an acute graft-versus-host reaction, Matsushima and colleagues (page 154) show that Peyer's patches (PPs) in the small intestine are critical for generating cytotoxic T cells (CTLs) against the host. The absence of PPs prevents these pathologic CTLs from developing (see also the News & Views by Ferrara, page 103). Painting in acrylic on paperboard by Christopher Cassidy.

Prodding T cells to action involves turning on some molecules while reducing the activity of others. ZAP-70 is one of the first kinases to be activated. Mustelin and colleagues (page 44) report that the phosphatase VHR (red) is then recruited to lipid rafts (green) and phosphorylated by ZAP-70. Phospho-VHR then inactivates the MAP kinase pathway that involves Erk2. Immune synapse in acrylic on paper was painted by Michael Malicki.