Roles of IgH and L chains and of surrogate H and L chains in the development of cells of the B lymphocyte lineage.
Proteins expressed from productively rearranged H and L chain gene loci have been implied in the regulation of Ig gene rearrangements during B lymphopoiesis. However, recent findings suggest that early B cell development can occur without expression of surrogate L chain, without deposition of microH chains into membranes, without productive H chain gene rearrangements, and even without any rearrangements of Ig gene loci. In bone marrow, 2-5% of all B220-, sIgM-, c-kit+ cells are pro B cells that undergo differentiation from B220- via B220+, c-kit+, CD43+, clonable long-term proliferating pre B-I cells to B220+, c-kit-, CD43-, IL-2 receptor+ pre B-II cells and immature B cells, only to die by apoptosis in situ within less than 4 days. A membrane-bound complex of surrogate H chain (gp130/gp35-65) and surrogate L chain expressed on pro B and pre B-I cells has apparently no influence on this early development. Pre B-I cells carrying DHJH-rearrangements in reading frame (rf) II are counter-selected, probably because they can express an Ig-like complex of truncated DHJHC mu-protein and surrogate L chain, while pre B-I cells DHJH-rearranged in rf I or III are not suppressed. Immature sIg+ B cells, also from bcl-2 transgenic mice, can continue to rearrange L chain gene loci. Thus, mere membrane deposition of Ig, even with concomitant expression of bcl-2, terminates neither expression of RAG-1 and 2, nor secondary L chain gene rearrangements, nor does it allow the development of mature B cells. Membrane-bound expression of an Ig-like complex of microH chains and surrogate L chains appears to be needed to generate the 50-70 million pre B-II cells in bone marrow. However, the membrane-bound expression of Ig is mandatory for negative and positive selection of immature B cells. Autoantigens delete or anergize self-reactive B cells. We speculate that all mature, resting, primary antigen-reactive B cells in the periphery have been selected from immature sIg+ B cells by unknown antigens and have, thereby, changed their lifestyle from rapid death by apoptosis to longevity.
Melchers
F
F
Basel Institute for Immunology, Switzerland.
Haasner
D
D
Grawunder
U
U
Kalberer
C
C
Karasuyama
H
H
Winkler
T
T
Rolink
A G
AG
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000502:physiology*; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000502:physiology*; D007147:Immunoglobulin Light Chains / Q000502:physiology*
D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains