CD4+ T cell subset differentiation and avidity setpoint are dictated by the interplay of cytokine and antigen mediated signals.

CD4(+) T cell differentiation has been shown to be regulated by the cytokine milieu present during activation as well as peptide MHC levels. However, the extent to which these two important regulatory signals work in concert to shape CD4(+) T cell function has not been investigated. Using a murine OT-II transgenic TCR model of in vitro differentiation, we demonstrate that the ability of CD4(+) T cells to commit to a distinct lineage, i.e. Th1 vs. Th2 vs. Th17, is restricted by the amount of peptide antigen present in the stimulating environment. In addition, whether cells succumb to inhibitory effects associated with high dose antigen is dependent on the array of cytokine signals encountered. Specifically, stimulation with high dose antigen in Th1 or Th17 conditions promoted efficient generation of functional cells, while Th2 polarizing conditions did not. Finally, we found that the peptide sensitivity of an effector cell was determined by the combined actions of cytokine and peptide level, with Th1 cells exhibiting the highest avidity, followed by Th17 and Th2 cells. Together, these data show that the interplay of antigen and cytokine signals shape both the differentiation fate and avidity setpoint of CD4(+) T cells.

Inter-kingdom signaling: deciphering the language of acyl homoserine lactones.

Bacteria use small secreted chemicals or peptides as auto-inducers to coordinately regulate gene expression within a population in a process called quorum sensing. Quorum sensing controls several important functions in different bacterial species, including the production of virulence factors and biofilm formation in Pseudomonas aeruginosa and bioluminescence in Vibrio fischeri. Many gram-negative bacterial species use acyl homoserine lactones as auto-inducers that function as ligands for transcriptional regulatory proteins. Several recent reports indicate that bacterial acyl homoserine lactones can also affect gene expression in host cells. Direct signaling also appears to function in the opposite direction as some eukaryotic cell types produce mimics that interact with quorum sensing systems in bacteria. Here, we will describe the evidence to support the existence of bi-directional inter-kingdom signaling via acyl homoserine lactones and eukaryotic mimics and discuss the potential molecular mechanisms that mediate these responses. The functional consequences of inter-kingdom signaling will be discussed in relation to both pathogenic and non-pathogenic bacterial-host interactions.

Construction of a bacterial autoinducer detection system in mammalian cells.

Quorum sensing (QS) is a cell density-dependent signaling system used by bacteria to coordinate gene expression within a population. QS systems in Gram negative bacteria consist of transcription factors of the LuxR family and their acyl homoserine lactone (AHL) ligands. We describe here a method for examining QS signaling systems in mammalian cells that uses engineered LuxR-type proteins from the opportunistic pathogen, Pseudomonas aeruginosa, which can function as AHL-dependent transcription factors. The engineered proteins respond to their cognate ligands and display sequence specific DNA binding properties. This system has several potential biotechnological and biological applications. It may be used to characterize any LuxR-type protein, screen animal and plant cell extracts or exudates for compounds that mimic or interfere with AHL signaling or to screen different cell types for AHL inactivating activities.