# Dendritic cells support IgA production in clonal B cell microculture

#### Abstract

Microcultures of helper T cells and a few appropriately primed murine B cells can be used to detect cognate T-B interactions which lead to clonal production of IgM, IgG1, and IgE. However, IgG2, IgG3, and IgA are very rarely expressed. We have found that the addition of DC to such cultures creates an extremely supportive environment for clones expressing IgA with other isotypes, as well as clones expressing only detectable IgA. Typically, 400 DC were added to 3000 conalbumin-specific T$\sb{\rm H}$ cells (D10.G4.1) and 30 hapten-specific PP B cells with antigen in 15 uL. The response was antigen dependent and clonal. Almost half of the clones expressed only non-IgM isotypes, 43% expressed some IgA, and 14% expressed some IgG3; isotype diversity increased over time. Cultures with B cells from LN, athymic nude mice, or surface IgD$\sp+$ cells were all found to switch to IgA production in microculture as judged by their generating clones expressing IgM along with IgA and other isotypes, and this was usually only in the presence of DC. DC from PP and spleen were found to be equally supportive, and allowed the number of T cells required in microculture to be decreased from 3000 to 400. However, T cell proliferation was not required for the supportive effect of DC, and the DC need not be MHC haplotype-matched with the T$\sb{\rm H}$ cells. Although DC induce an Ag-dependent increase in IL-4 and IL-6 production by D10.G4.1, culture medium from Ag/T/DC cultures does not substitute for DC in T/B cultures to allow IgA expression. As IgA is not expressed in cultures with DC, B cells, and mitogens ($\pm$ added CAS from D10.G4.1), T$\sb{\rm H}$ cells appear to be necessary at some stage for the DC effect. Cyclosporin A inhibition of Ig production in T/B microcultures is overcome by the addition of DC without requiring exogenous lymphokines, and IgA production in T/B/DC cultures is barely affected by this drug. The data suggest a contact-mediated mechanism which may involve a CyA-insensitive signalling pathway such as the CD28/B7 pathway which results in sustained, increased lymphokine output by T$\sb{\rm H}$ cells.

Immunology

#### Recommended Citation

Schrader, Carol Elizabeth, "Dendritic cells support IgA production in clonal B cell microculture" (1992). Dissertations available from ProQuest. AAI9235200.
https://repository.upenn.edu/dissertations/AAI9235200

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