In vitro IgE but not IgG production of canine peripheral blood B cells is inhibited by CD40 ligation.

The aim of this study was to investigate in vitro IgE induction in peripheral canine B cells. CD21(+) B cells were purified from the peripheral blood of beagle dogs by positive selection via magnetic separation to a purity of >/=95%. Subsequently, proliferation, and IgG and IgE production of canine B cells were investigated after stimulation with human recombinant Interleukin-4 (hrIL-4) and human recombinant Interleukin-2 (hrIL-2) in the presence or absence of CD40L-CD8 fusion protein (CD40L) of mouse origin. We could demonstrate that canine B cells react on hrIL-2 alone by proliferation and IgG production but not by IgE secretion, whereas activation with hrIL-4 induced proliferation and mainly IgE production. Together, both cytokines synergistically increased B cell proliferation as well as IgG and IgE production. We could also show that mouse CD40L induces proliferation of dog B cells, which is further enhanced by addition of hrIL-4. Unexpectedly, CD40L led to a dramatic decrease in the IL-4 mediated IgE secretion (82% inhibition on an average). In contrast, IgG production was not affected significantly by CD40L. The same effects of CD40L were observed when B cells were stimulated by a combination of IL-2 and IL-4 and this inhibition could not be abrogated by increasing the amounts of IL-4. In summary, activation of canine B cells from peripheral blood by hrIL-4 in the presence or absence of hrIL-2 led to marked IgE production that is strongly and in a dose-dependent manner inhibited by CD40L. Stimulation of IgG production is not influenced by CD40L.

Interaction of auxin-binding protein 1 with maize coleoptile plasma membranes in vitro.

In a search for membrane "docking proteins" interacting with Zea mays auxin-binding protein (ABP1) the binding of purified ABP1 to maize coleoptile plasma-membrane vesicles was investigated. Concentration-dependent, saturable binding of ABP1 to the membrane vesicles was observed in binding assays using 10(-8)-10(-6) M ABP1. Biotinylated ABP1 was displaced from the membrane binding sites by competition with unlabeled ABP1, demonstrating specific binding. The association step proved to be pH-dependent with maximum binding at pH 5.0 or lower. Auxins did not influence the ABP1 binding to plasma-membrane vesicles, but ABP1 associated with plasma-membrane vesicles was still able to specifically bind [3H]naphthalene-1-acetic acid. The rather stable interaction of ABP1 with plasma-membrane vesicles was only affected by strong alkaline buffers or detergents. The binding capacity was calculated to be in the range of 0.2 pmol ABP1 per g coleoptile fresh weight.