Several new functions have been assigned to basophils, including involvement in promoting T helper type 2 immunity. Booki Min (p 1333) reviews the recent literature on basophils analyzing what they 'can do' in vitro and what they 'actually do' during in vivo immune responses. Artwork by Lewis Long.

Like stamens protruding from flowers, phosphorylated serine residues protrude from phosphopeptides presented by HLA-A2 molecules. Engelhard and colleagues (p 1236) suggest that the greater HLA-A2- binding affinity afforded by these phosphorylated residues allows phosphopeptides bearing suboptimal 'anchor' residues to interact with HLA-A2 molecules through an unorthodox binding mode. Artwork by Lewis Long.

Like locks moving boats along an upward-sloping canal, transcription factors propel thymocytes through various stages of T cell development. Three papers in this issue (pp 1113, 1122 and 1131; see also News and Views, p 1095) suggest that GATA-3 is needed for initial specification to the CD4+ lineage, whereas ThPOK, by suppressing Runx activity and by maintaining expression of ThPOK and CD4, acts later to prevent diversion toward a CD8+ cell fate. Artwork by Lewis Long.

Immune cells are constantly on the go. Circulating leukocytes respond to many chemoattractants that direct their exit from the bloodstream and their entrance into and exit from tissues. This month, we present a series of commissioned review articles focusing on the trafficking patterns of migrating immune cells. Additional discussion of relevant ongoing research topics is available online (www.nature.com/ni/focus/trafficking/index.html). Artwork by Lewis Long.

CD8+ T cells mediate protection against the parasite Toxoplasma gondii. Shastri and colleagues (p 937; News and Views by Jensen, p 829) identify an immunodominant T. gondii peptide whose production requires processing by the aminopeptidase ER AAP. The original image, generated by two-photon laser-scanning microscopy, shows a cyst containing T. gondii (red) surrounded by antigen-presenting cells (green) and T cells (blue) in the brain of an infected mouse. Original image by M. Schaeffer. Art work by Lewis Long.

Bacterial flagellin binds to and stimulates TLR5. Akira and colleagues (p 769) show that TLR5 stimulation of CD11chiCD11bhi small intestine lamina propria DCs induces the release of retinoic acid, which promotes the differentiation of IgA-producing B cells and IL-17-producing T cells. The original image (by Satoshi Uematsu and Jang Myoung Ho) shows CD11chiCD11bhi small intestine lamina propria DCs (purple). Artwork by Lewis Long.

Some viral infections destroy lymph node stromal cells. Scandella et al. (p 667) demonstrate that the restoration of lymph node integrity requires lymphoid tissue-inducer cells and signaling via lymphotoxin α1β2. Original image shows splenic sections immunostained for B220 (blue) and Thy-1.2 (green) to define B and T cell zones and with anti-gp38 to visualize T cell zone stromal cells. Original image by Elke Scandella. Artwork by Lewis Long.

In response to viruses, plasmacytoid dendritic cells (pDCs) produce interferon-α. Connolly and colleagues (p. 551; News and Views by Pulendran, p. 461) show that pDCs also rapidly internalize exogenous viral antigens and present them on major histocompatibility complex class I to CD8+ T cells. The original image shows the pDC major histocompatibility complex class I compartment (red), nuclei (blue) and actin (green). Original image by Sandra Clayton. Artwork by Lewis Long.

The bone marrow contains specialized niches that support hematopoiesis. Jung and colleagues (p 388) identify a new dendritic cell subset that provides survival factors for mature B cells residing in the bone marrow. The original image shows perivascular dendritic cells (green) and blood vessels (red) in mouse skull bone marrow. Image by Anita Sapoznikov & Vyacheslav Kalchenko. Artwork by Lewis Long.

Lampreys express a diverse repertoire of variable lymphocyte receptors (VLRs). Cooper and colleagues (p 319) identify VLRB-producing cells that resemble mammalian B cells in the lamprey. A lamprey is shown in the foreground, and lamprey gill tissues immunostained for VLRB (green) and BrdU (red) are shown in the background; nuclei are stained with DAPI (blue). Artwork by Lewis Long.

Although tightly regulated in healthy animals, leukocyte migration into the central nervous system runs awry in neuroinflammatory disorders. Prat and colleagues (p 137) show that ALCAM, an adhesion molecule expressed on blood-brain barrier endothelial cells, promotes the entry of pathogenic leukocytes into the central nervous system. The original micrograph shows human CD4+ T cells (green) migrating across human blood-brain barrier endothelial cells expressing ALCAM (red) in vitro. Artwork by Lewis Long.

Whether type I and type II interleukin 4 receptors exert distinct functions in vivo is not known. Using a mouse lacking the type II interleukin 4 receptor component IL-13Rα1, Wynn and colleagues delineate unique functions of this receptor in vivo (p 25). The original image (bottom) captured under polarized light shows diminished collagen content in the liver of an IL-13Rα1-deficient mouse infected with Schistosoma mansoni. Artwork by Lewis Long.