Factors influencing function: Activation of antigen presenting cells by the cholera toxin B-subunit, and regulation of the cholinergic phenotype in nerve growth factor receptor-positive basal forebrain cholinergic neurons by bone morphogenetic protein 9

This dissertation describes two projects examining the effects of factors that modulate cellular function. Cholera toxin (CT) is one of the most effective and widely studied mucosal adjuvants. Although the ADP-ribosylating A-subunit has been implicated in augmenting immune responses, the receptor binding B-subunit (CT-B) has greater immunogenicity, and may be a repository of adjuvant activity, absent of potential toxicity. In cultured primary murine B cells and macrophages, CT-B caused an increase in the phosphorylation of multiple signaling molecules including Erk1/2 and p38. CT-B also induced the transactivation of the transcription elements CRE and NF-kappaB, the latter of which was abolished by tyrosine kinase inhibition. Although specific inhibitors of MEK1/2 did not reduce CT-B induction of cell surface marker expression, they attenuated CT-B mediated secretion of IL-6. These data show that CT-B induces a set of signaling events related to immune cell activation, surface molecule expression and cytokine production that has potential implications in elucidating CT-B adjuvant activity in the absence of enzymatically active CT-A.;The activity of the basal forebrain cholinergic neurons (BFCN) that innervate the cerebral cortex and hippocampus is essential for normal learning and memory. To examine the development of these neurons, BFCN were purified from murine embryonic septum by fluorescence-activated cell sorting, based on their expression of the neurotrophin receptor p75, a surface marker for mature BFCN. p75+ cells were enriched in choline acetyltransferase (ChAT) and the high-affinity choline transporter (ChT), and maintained expression of these cholinergic markers in vitro, whereas p75- cells had a low expression of these genes. Bone morphogenetic protein 9 (BMP9), which induces the cholinergic phenotype in heterogeneous septal cultures, had little effect on already high p75 and ChAT gene expression in p75+ cells, but it increased expression of these genes in p75- cells. Conversely, ChT gene expression was decreased in p75+ cells and was relatively unchanged in p75- cells. Only a subset of p75- cells increases p75 protein levels in response to BMP9. These data suggest that BMP9 induces the cholinergic phenotype in a set of non-cholinergic or precursor cells in the forebrain.