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Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
The extent of allelic exclusion in Ig genes is very high, although
not absolute. Thus far, it has not been clearly established whether
rapid selection of the developing B cell as soon as it has achieved the
first productively rearranged, functional heavy chain is the only
mechanism responsible for allelic exclusion. Our computational models
of Ag receptor gene rearrangement in B lymphocytes are hereby extended
to calculate the expected fractions of heavy chain allelically included
newly generated B cells as a function of the probability of heavy chain
pairing with the surrogate light chain, and the probability that the
cell would test this pairing immediately after the first rearrangement.
The expected fractions for most values of these probabilities
significantly exceed the levels of allelic inclusion in peripheral B
cells, implying that in most cases productive rearrangement and
subsequent cell surface expression of one allele of the heavy chain
gene probably leads to prevention of rearrangement completion on the
other allele, and that additional mechanisms, such as peripheral
selection disfavoring cells with two productively rearranged heavy
chain genes, may also play a role. Furthermore, we revisit light chain
allelic exclusion by utilizing the first (to our knowledge)
computational model which addresses and enumerates B cells maturing
with two productively rearranged
light chain genes. We show that,
assuming that there are no selection mechanisms responsible for
abolishing cells expressing two light chains, the repertoire of newly
generated B lymphocytes exiting the bone marrow must contain a
significant fraction of such
double-productive B
cells.
This article has been cited by other articles:
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R. Mehr, H. Edelman, D. Sehgal, and R. Mage Analysis of Mutational Lineage Trees from Sites of Primary and Secondary Ig Gene Diversification in Rabbits and Chickens J. Immunol., April 15, 2004; 172(8): 4790 - 4796. [Abstract] [Full Text] [PDF] |
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