Schematic representation of lymphocyte development and activation. Development of lymphocytes takes place in primary lymphoid organs as the bone marrow (BM) and the thymus. Long-term hematopoietic stem cells (LTSCs) generate short-term hematopoietic stem cells (STSCs), which in turn generate common myeloid and lymphoid progenitors (CMP and CLP, resp.,). T cell progenitor, migrate to the thymus, where they undergo maturation through stages known as double negative (DN), representing CD4-CD8- cells, double positive, and finally mature CD4+ or CD8+ T cells. Immature B cells leave the bone marrow to finish their development in the spleen, where they progress through transitional stages 1 and 2 (T1 and T2) to generate mantle-zone B cells (MZ B cells), follicular B cells, or B1 cells. All mature lymphocytes circulate through secondary lymphoid organs, where they are exposed to antigens, directly or through antigen presenting cells. After the first stimulation by antigens, B and T cells migrate towards each other to interact in a process that will determine B cell antibody production and T cell proliferation and further activation. The immunological synapses are represented between a dendritic cell and a naive T cell and between primed B and T cells. In detail, one may observe molecules present in immunological synapses.
