ABSTRACT
OT-II mice were evaluated as a transgenic strain-specific model to assess T-cell help for B-cell responses. OT-II CD4(+) T-cells express transgenic OVA-specific αß-TCRs. This high frequency of antigen-specific helper T-lymphocytes may augment induction of B-cell responses. Unexpectedly, OT-II mice did not produce OVA-specific antibodies after intranasal immunization. However, B-cells expressed normal antigen-presenting function in vitro for activation of OVA-specific T-cell responses. These OT-II T-cell responses produced a Th1-type cytokine profile with significantly reduced Th2 or Th17 responses. These data suggest that OT-II B-cells are not defective as APCs, however, downstream antibody responses are abrogated in this transgenic strain.
Subject(s)
Antibodies/immunology , Ovalbumin/immunology , Receptors, Antigen, T-Cell/immunology , Vaccination/methods , Animals , B-Lymphocytes/immunology , B-Lymphocytes/metabolism , Cells, Cultured , Cholera Toxin/immunology , Coculture Techniques , Cytokines/immunology , Cytokines/metabolism , Enzyme-Linked Immunosorbent Assay , Immunoglobulin G/blood , Immunoglobulin G/immunology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Receptors, Antigen, T-Cell/genetics , T-Lymphocytes, Helper-Inducer/immunology , T-Lymphocytes, Helper-Inducer/metabolism , Th1 Cells/immunology , Th1 Cells/metabolismABSTRACT
A common topology found in many bistable genetic systems is two interacting positive feedback loops. Here we explore how this relatively simple topology can allow bistability over a large range of cellular conditions. On the basis of theoretical arguments, we predict that nonlinear interactions between two positive feedback loops can produce an ultrasensitive response that increases the range of cellular conditions at which bistability is observed. This prediction was experimentally tested by constructing a synthetic genetic circuit in Escherichia coli containing two well-characterized positive feedback loops, linked in a coherent fashion. The concerted action of both positive feedback loops resulted in bistable behavior over a broad range of inducer concentrations; when either of the feedback loops was removed, the range of inducer concentrations at which the system exhibited bistability was decreased by an order of magnitude. Furthermore, bistability of the system could be tuned by altering growth conditions that regulate the contribution of one of the feedback loops. Our theoretical and experimental work shows how linked positive feedback loops may produce the robust bistable responses required in cellular networks that regulate development, the cell cycle, and many other cellular responses.
