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J Purkerson

Publications and source records attributed to J Purkerson.

3 recordsLinked to original sources
PubMed1992

A two-signal model for regulation of immunoglobulin isotype switching.

A characteristic feature of the humoral immune response is a switch from IgM to other Ig isotypes that typically occurs subsequent to a first exposure to antigen. Ultimately, isotype switching involves a DNA rearrangement that recombines a variable region gene, initially juxtaposed to the mu constant region gene (C mu), with a constant region gene located downstream of C mu. Isotype switching is controlled by T lymphocyte-derived cytokines, such as interleukin-4 (IL-4), gamma-interferon (gamma-IFN), and TGF beta, which direct B lymphocytes to switch to specific Ig classes. For example, IL-4, directs murine B cells to produce IgG1 and IgE, and human B cells to produce IgE and IgG4. IL-4 appears to direct switching to IgE and IgG1 by inducing transcription of the epsilon and gamma 1 constant region genes before switch recombination. However, IL-4 is not a sufficient stimulus for isotype switching, and additional signals are required to complete this process. This second signal can be provided by physical contact with activated T cells, which may involve, at least in part, ligation of the CD40 molecule. For murine B cells the second signal may also be provided by IL-5. Isotype switching in B lymphocytes may provide a useful model for directed DNA recombination in higher eukaryotes.

Animals↗
PubMed1991

A novel method for synchronizing a B cell lymphoma.

Certain sub-lines of the murine B cell lymphoma BCL1 can be maintained in vitro and respond to cytokines including IL-2 and IL-5. BCL1 cells, as well as other B lymphomas, are difficult to synchronize using conventional techniques such as thymidine block or DNA synthesis inhibition. We have found that BCL1 cells maintained in Dulbecco's minimum essential medium (DMEM) with non-essential amino acids (NEAA) can be readily synchronized by culture in DMEM lacking NEAA. Within 10-18 h of medium replacement, 98% of BCL1 cells are 2 N in DNA content, suggesting that these cells are arrested in G0/G1. This population of BCL1 cells is viable and can be stimulated to enter S phase by culture in media containing NEAA; however, arrested cells did not appear to return synchronously into the cell cycle on addition of NEAA. A transient increase in levels of c-fos and c-myc mRNA was not detected after arrested BCL1 cells were stimulated to enter S phase, suggesting that arrested cells are in the G1 phase of the cell cycle, rather than G0. This technique for obtaining G1 arrested B lymphoma cells may prove useful in the analysis of molecular events that occur in B cells as a function of cell cycle position.

Amino Acids↗