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J Roes

Publications and source records attributed to J Roes.

22 records · Page 2Linked to original sources
PubMed1991

Cell autonomous expression of IgD is not essential for the maturation of conventional B cells.

To analyse the function of IgD in vivo, we generated a 'loss of function' mouse model utilizing gene targeting technology. By homologous recombination in a (C57BL/6 x CBA)F1 mouse embryonic stem cell (ES) line one allele of the delta heavy chain gene was rendered non-functional. In chimeric mice obtained after injection of the targeted ES cells into blastocysts derived from severe combined immunodeficient mice we analysed ES cell derived B lymphocytes expressing the targeted or the wild-type allele by using allotype specific reagents. We show that B cells expressing the targeted allele appear in the periphery as IgM+ D- cells at normal frequency. They express the CD23 marker and respond to a T cell dependent antigen. Thus, cell autonomous expression of IgD is neither essential for B cell maturation into an antigen responsive state nor for antigen dependent triggering of the cells into an immune response.

Animals↗
PubMed1989

V gene rearrangement is required to fully activate the hypermutation mechanism in B cells.

Nonproductively rearranged H and L chain loci of B cell hybridoma lines expressing heavily mutated antibodies were cloned and partially sequenced. The results confirm earlier data showing that somatic point mutations are as frequent in nonproductively rearranged loci containing a rearranged V gene as in productively rearranged loci. They establish in addition that in nonproductive H chain loci which bear a DJH rearrangement the frequency of somatic mutations is more than 10 times lower (0.2%) than in VDJH loci expressed by the same cells (2.5%). Thus, the hypermutation mechanism operating in B cell differentiation is targeted at V genes rearranged to the J locus and may require nucleotide sequences associated with both V and J elements in order to be fully activated. An inversion of the JH2 segment was detected in one DJH locus. This inversion appears to be the result of a secondary joining event occurring occasionally in the course of B cell development.

Animals↗
PubMed1987

Timing, genetic requirements and functional consequences of somatic hypermutation during B-cell development.

While somatic antibody mutants are rare in the preimmune repertoire and in primary immune responses, they dominate secondary and hyperimmune responses. We present evidence that somatic hypermutation is restricted to a particular pathway of B-cell differentiation in which distinct sets of B-cell clones are driven into the memory compartment. In accord with earlier results of McKean et al. (1984) and Rudikoff et al. (1984), somatic mutation occurs stepwise in the course of clonal expansion, before and after isotype switch, presumably at a rate close to 1 X 10(-3) per base pair per generation. At this rate, both selectable and unselectable mutations accumulate in the rearranged V region genes. The distribution of replacement mutations in the V regions shows that a fraction of the mutations in CDRs is positively selected whereas replacement mutations are counterselected in the FRs. By constructing an antibody mutant through site-specific mutagenesis we show that a point mutation in CDR1 of the heavy chain, found in most secondary anti-NP antibodies, is sufficient to increase NP binding affinity to the level typical for the secondary response. Somatic mutation may contribute to the immune repertoire in a more general sense than merely the diversification of a specific response. We have evidence that clones producing antibodies which no longer bind the immunizing antigen can be kept in the system and remain available for stimulation by a different antigen. Somatic mutations are 10 times less frequent in DJH loci than in either expressed or non-expressed rearranged VDJH or VJ loci. We therefore conclude that a V gene has to be brought into the proximity of the DJH segment in order to fully activate the hypermutational mechanism in these loci.

Animals↗