Evidence for the stochastic acquisition of cytokine profile by CD4⁺ T cells activated in a T helper type 2‐like response in vivo

Abstract

The diversity of cytokine production patterns displayed by T cells activated in vivo was investigated by analyzing short-term antigen-specific CD4+ T cell clones and single CD4+ T cells derived from draining lymph nodes of mice undergoing a T helper 2 (Th2)-like response to keyhole limpet hemocyanin (KLH). On average, 2.7% of CD4+ lymph node cells gave rise to clones in the presence of the immunizing antigen and, of these, about 90% secreted interleukin-4 (IL-4) and 20% secreted interferon-gamma (IFN-gamma) when restimulated after 2 weeks in vitro. Almost all IFN-gamma-producing clones co-produced IL-4. The definition of clones as positive or negative for cytokine synthesis depended on assay sensitivity, however, since their titers were distributed continuously from the threshold of detection over at least a 1000-fold range. Reverse-transcription polymerase chain reaction analysis of 59 clones revealed multiple patterns of co-expression of IL-2, IL-3, IL-4, IL-6, IFN-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA. Although most clones contained detectable IL-4 and IL-6 mRNA and a minority contained IFN-gamma mRNA, only 1 clone expressed the canonical Th2 cytokine profile. The observed frequencies of mRNA co-expression for most of the six cytokines (including IL-4 with IFN-gamma), and the frequency of co-secretion of IL-4 and IFN-gamma, were not significantly different from those predicted for random association. Independent regulation of IL-4 and IFN-gamma mRNA expression was confirmed at the single-cell level in a polyclonal population of KLH-primed CD4+ cells, among which co-expression of these cytokines again occurred at the frequency predicted for a random event. The data suggest that the polarization of this immune response towards a Th2 cytokine profile is achieved by altering the probabilities of expression of the IL-4, IFN-gamma and other cytokine genes at the population level, rather than by selective expansion of a distinct T cell subset.

The Kinetics of In Vivo Priming of CD4 and CD8 T Cells by Dendritic/Tumor Fusion Cells in MUC1-Transgenic Mice

“…The heterogeneity of cytokine profiles has been extensively demonstrated (43)(44)(45). The diversity of cytokine production patterns reflects the polyclonal populations of activated T cells rather than the cytokine profile of an individual cell (43,44). These results are consistent with our findings that immunization with fusion cells induces polyclonal T cell responses (24).…”

“…However, both types of T cells have been shown to participate in the antitumor immune response (37)(38)(39)(40)(41)(42). The heterogeneity of cytokine profiles has been extensively demonstrated (43)(44)(45). The diversity of cytokine production patterns reflects the polyclonal populations of activated T cells rather than the cytokine profile of an individual cell (43,44).…”

Why the immune system takes its chances with randomness

“…Other immune examples of stochastic processes include the probabilistic expression of cytokines 5,6 and the combinatorial expression of natural killer cell receptors in a population 7 .…”

“…This hypothesis has been tested by asking what remains when such structures are removed. We and others find a great deal of cell fate heterogeneity under simple in vitro culture conditions [4][5][6]12,13 . Conversely, crucial molecular contributors to early developmental programmes, including asymmetric cell division, do not alter B cell or T cell responses in vivo 14 .…”

Nature versus nurture in T cell cytokine production

“…The diversity of cytokine expression patterns seen in polyclonal T cell populations and T cell clones has been shown to exceed the type 1 and type 2 patterns [3][4][5][6]. Incontrovertible studies have detected simultaneous expression of multiple type 1 and type 2 cytokine mRNAs or proteins in single T cells [7][8][9][10][11]. New categories such as Th3 or Tr1 [12,13] have been proposed to accommo-date a few of these unconventional patterns.…”