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All cells of the immune system are derived from precursor cells in the bone marrow known as haematopoietic stem cells (HSCs). This Review describes recent advances in our understanding of the specialized bone-marrow niches that regulate HSC differentiation and self-renewal.
Recent studies have identified potential factors and cellular environments that foster B-cell development in the bone marrow. As discussed, knowledge of such microenvironmental niches and of B-cell precursor populations has advanced our understanding of the spatiotemporal regulation of B-cell development.
Although T cells are derived from haematopoietic stem cells in the bone marrow, T-cell development occurs in the thymus. This Review describes recent data indicating that several cell populations in the bone marrow are able to populate the thymus and generate T cells.
As thymocytes travel through the thymus, they not only receive signals from stromal cells but also deliver signals to stromal cells to generate the appropriate stromal environment. Takahama describes the factors involved in this lympho–stromal crosstalk for thymocyte trafficking and T-cell-repertoire selection.
Different pathogens have evolved distinct strategies to promote their survival in host cells. This Review describes the contribution of the endoplasmic reticulum to host defence and the mechanisms by which pathogens interacting with the endoplasmic reticulum subvert the host immune response.
Mucosal immunization could be our best hope for protection against pathogens that infect mucosal tissues. Here, the authors describe how our accumulating knowledge of the mechanisms of mucosal immune defence is being applied to mucosal vaccine design, in particular against HIV.
Recent data indicate that chemokines have a role in regulating dendritic-cell maturation. In this Opinion article it is proposed that this ensures that dendritic cells migrating to the lymph node arrive in a fully mature state that is optimal for T-cell priming.
All the cells of the immune system are derived from precursor cells in the bone marrow. However, full development to become a T cell is completed in the thymus, not in the bone marrow as is the case for B cells. This Focus highlights our current understanding of several steps that are crucial for the complex process of early lymphocyte development.