News & Views

The proliferation and differentiation of hematopoietic stem cells is regulated by BMP-4 and Shh. These factors collaborate with cytokines in the bone marrow to create an environment that maintains stem cell homeostasis

Human hematopoietic stem cells are of vital scientific and clinical importance. Using high resolution clonal analysis, Dick and colleagues shed important new light on the developmental behavior of these cells in the context of an in vivo model system.

The immunomodulatory character of bacterial CpG DNA is well known. A report in a recent issue of Nature pinpoints a Toll-like receptor as the cellular accomplice in this innate immune reaction.

Remodeling of chromatin, distinct from activation of NF-κB, is a newly identified function of Toll-like receptors in mammals. In Drosophila , Toll receptors play a role in development as well as immunity; yet in mammals, they have an immunological role only. Further clues to the evolutionary development of the Toll receptors are emerging.

The newly rearranged T cell receptor on the surface of immature thymocytes must interact with not too much and not too little affinity for self-peptide–MHC ligands to allow the cell to mature and emigrate to the lymphoid periphery. Recent experiments shed new light on how the signal is perceived as “just right”.

Until now, the function of OX2 has been unclear. Now, with the cloning of its receptor and the generation of OX2^−/− mice, a possible role as an inhibitor for myeloid activation has emerged.

NKT cells can rapidly produce a diversity of immunoregulatory cytokines; does this make these cells aggressors or suppressors? New experiments now reveal their immunosuppressive function in tumor control and reiterate their pivotal position.

Although thyrocytes in two autoimmune diseases of the thyroid both express Fas and FasL, the conditions produce opposite results: either hyper- or hypothyroidism. This may be due to cytokine production indirectly supporting pro- or anti-apoptotic gene expression in thyrocytes.

“Lymphocyte subsets” brings to mind different types of T cells. New work indicates that B cells may also have distinct effector functions

The bite of the sandfly can both bring disease or provide protection. A report in a recent issue of Science indicates that infection with Leishmania can be severely impaired by previous bites from uninfected sandflies.

A recent paper in Nature sheds welcome light on the mechanism of somatic hypermutation by documenting the participation of double-strand DNA breaks.

Once natural killer cells identify their targets they engage their lysis machinery. Spontaneous, unlike antibody-dependent, cytotoxicity predominantly uses a Ras-independent pathway to accomplish this activation.

The innate immune system relies heavily upon Fc receptors to rid the body of pathogens. An Fc receptor that recognizes IgM has finally been cloned.

Lymphocyte memory—is there a requirement for the continual presence of antigen or not? In a recent issue of Nature an elegant series of genetic manipulations from Maruyama et al. makes a strong case for the persistence of B cell memory in the absence of antigen.

In a new twist, the cytokine IL-10, if present when leukocytes are activated, can disconnect chemokine receptors from signaling for cell migration. The receptors act as a “sink” for soaking up chemokines, thus providing the perfect decoy.

B cell maturation is affected by factors found in the microenvironment of the bone marrow. A new tachykinin neuropeptide family member, HK-1, and TSLP both seem to aid the pre-B cell stage.

The NF-κB family of transcription factors are central to signaling from Toll family receptors. The IKKγ protein of Drosophila has been found to regulate NF-κB family–member Relish, but not the similar protein DIF, in the fly innate immune response.

Ever since it was proposed that distinct subsets of dendritic cells induce distinct subsets of T cells, immunologists have been struggling to reconcile those conclusions with other data. New experiments now illuminate a different interpretation.

How do T cells recognize allogeneic MHC molecules with such ferocity? The first crystal structure of an allo-MHC complexed with peptide and T cell receptor begins to reveal the answer.

Antigen receptor editing is no longer the province of B cells alone. T cells also can be caught in the act, given the right system. The T cell receptors of double positive thymocytes that recognize self antigens on the cortical epithelium with dangerously high affinity will undergo editing until they get it right.