| Speaker: |
Motokazu Tsuneto
Max Planck Institute for Infectionbiology |
| Title: |
B cell progenitors and precursors change their microenvironment in fetal liver during early development |
| Summary : | The microenvironments, in which B-lymphocytes develop in fetal liver, are largely still unknown. Among the non-hematopoietic cells we have identified and FACS-separated two subpopulations, CD45-TER119-VCAM-1+ cells that are either CD105highLYVE-1high or CD105lowALCAMhigh. Immunohistochemical analyses find three of four c-Kit+IL-7Rα+B220lowCD19-SLC- B-progenitors in contact with vascular endothelial-type LYVE-1high cells on embryonic day 13.5. One day later c-Kit+IL-7Rα+ cells develop to CD19- and +, SLC-expressing, DHJH-rearranged pre/pro and pro/preB-I cells. Less than 10% are still in contact with LYVE-1high cells, but half of them are now in contact with mesenchymally-derived ALCAMhigh liver cells. All of these ALCAMhigh cells, but not the LYVE-1high cells produce IL-7 and CXCL12, while both produce CXCL10. Progenitors and pro/preB-I cells are chemo-attracted in vitro towards CXCL10 and 12, suggesting that lymphoid progenitors with Ig gene loci in germline configuration enter the developing fetal liver at E13.5 from vascular endothelium, attracted by CXCL10, and then migrate within a day to an ALCAMhigh liver cell-microenvironment, differentiating to DHJH-rearranging, surrogate light chain-expressing pre/proB and pro/preB-I cells, attracted by CXCL10 and 12. Between E15.5 and E16.5 preB-I cells expand 10 fold in continued contact with ALCAMhigh cells, and begin VH- to DHJH-rearrangements in further differentiated c-Kit-IL-7Rα- preBII cells. |
