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Biomedical subjects

M Scharff

Publications and source records attributed to M Scharff.

5 recordsLinked to original sources
PubMed1985

Isolation and characterization of anti-monosialoganglioside monoclonal antibody 19-9 class-switch variants.

Three different monoclonal antibody isotypes, IgG1, IgG2b, and IgG2a, were derived by selection of isotype-switch variants from the CO-19-9 hybridoma. All three antibodies retained their binding specificities and affinities and bound to the same epitope--as defined by the anti-idiotype analysis. Availability of gamma 1, gamma 2b, and gamma 2a Ig heavy chain variants directed against the same epitope on the monosialoganglioside antigen permitted detailed analysis of their Fc fragment receptor (FcR) binding affinities, their cytolytic activities (antibody-dependent, macrophage-mediated cytotoxicity) in vitro, and their tumoricidal activities in vivo. Analysis of the binding of three isotypes to the human FcR expressed by U937 cells induced by gamma interferon has shown that only IgG2a proteins bound to high-affinity FcR, but not IgG1 or IgG2b variants. Although all three isotypes were active in the antibody-dependent, macrophage-mediated cytotoxicity assay with murine thioglycolate-elicited macrophages, the IgG2a gave the highest percentage of lysis; similar results were obtained in the same assay with human monocytes as effector cells. In the nude mice experiment, only the IgG2a variant inhibited growth of human colorectal carcinoma, while IgG1 and IgG2b were ineffective. Thus, selection of isotype-switch variants resulted in the conversion of monoclonal antibody from noncytolytic to cytolytic with possible immunotherapeutic application.

Animals↗
PubMed1981

Recombination events that activate, diversify, and delete immunoglobulin genes.

Immunoglobulin kappa light-chain diversity arises, in large part, from an array of germ-line V-region genes that undergo somatic recombination with one of four active J-region segments. The diversity provided by this combinational system is increased by a recombination mechanism that allows variation of crossover points so as to generate additional diversity at a critical region of the light chain. The elaborate mechanism for generating diversity is accompanied not only by considerable waste, in terms of unused V and J regions in a given cell, but also by a range of aberrant recombinants that fail to produce active immunoglobulin genes.

Animals↗
PubMed1980

Immunoglobulin V/J recombination is accompanied by deletion of joining site and variable region segments.

A site-specific recombination event is responsible for the somatic activation of immunoglobulin genes and for generating a major share of immunoglobulin gene diversity. Although several possible mechanisms can be proposed to account for this process, recombinatio accompanied by deletion is a particularly attractive mechanism because it might utilize inverted repeat sequences noted on the 3' side of all variable regions and on the 5' side of all joining site segments thus far studied. Testing this model is complicated by the fact that antibody cells are at least diploid and gene segments on the inactive chromosome can obscure deletions occurring within the active gene. Accordingly, we have screened several immunoglobulin-producing plasmacytoma lines to select those in which both chromosomes are rearranged. By using appropriate cell lines and variable and joining region probes in in situ hybridization experiments, we show that recombination is accompanied by the deletion of both variable and joining region genes. These experiments also allow us to map the site of V/J recombination of several active immunoglobulin genes and suggest an order and orientation for variable, joining, and constant region sequences.

Animals↗