Surface Expression of the IFN-γR2 Chain Is Regulated by Intracellular Trafficking in Human T Lymphocytes

Abstract

The surface and cytoplasmic expressions of the transducing chain (IFN-γR2) of the heterodimeric IFN-γ receptor on human T lymphocytes have been investigated. We show that its surface expression is low, whereas high cytoplasmic levels are found in both resting and PHA-activated T lymphocytes. This low expression does not prevent activated T cells from responding to IFN-γ, because it induces IFN-regulatory factor 1 expression. Low surface IFN-γR2 expression appears to be due to recycling between cytoplasmic stores and the cell surface, which does not depend on signals mediated by endogenous IFN-γ, because IFN-γR2 surface expression is low, and its internalization is equally observed in patients with inherited IFN-γR1 gene deficiency and in healthy donors. Moreover, IFN-γR2 internalization in T lymphoblasts from healthy donors was not affected by the presence of anti-IFN-γ-neutralizing or anti-IFN-γR1-blocking mAb. In conclusion, these data illustrate a new mechanism whereby human T cells limit the surface expression of IFN-γR2 in a ligand-independent manner.

IGF-1 down-regulates IFN-γR2 chain surface expression and desensitizes IFN-γ/STAT-1 signaling in human T lymphocytes

“…We have previously shown that in human T lymphoblasts, internalization of IFN-␥R2 induces at least a 2-fold increase of cell-associated specific fluorescence of anti-IFN-␥R2 mAb uptake after 4-hour incubation at 37°C. 17 In ST4 cells cultured with serum for 24 hours, an about 2-fold increase of cell-associated specific fluorescence of anti-IFN-␥R2 mAb uptake was observed after 4-hour incubation at 37°C ( Figure 3A). In contrast, no anti-IFN-␥R2 mAb uptake was observed on ST4 cells cultured for 24 hours in the absence of serum ( Figure 3A), indicating that IFN-␥R2 internalization was inhibited.…”

“…13 The fact that IFN-␥R2 protein is prevalently accumulated in the cytoplasm of these malignant T-cell lines 13 underlies an IFN-␥-independent IFN-␥R2 internalization mechanism. 17 Since these T-cell lines express high surface levels of IGF-1R and do not secrete IGF-1 (Schillaci et al 28 and data not shown), we evaluated the effect of IGF-1 (100 ng/mL) on IFN-␥R2 internalization when they were cultured in the absence of serum. Since insulin, which is also present in serum, 29 activates IGF-1R, although at 10-fold higher concentration than IGF-1, 30 a 36-fold higher concentration of insulin was used to assess the specificity of action of IGF-1 on IFN-␥R2 expression.…”

“…Cell surface-associated mAb was removed by treating twice with acid pH (2 minutes at pH 3.0) as described. 17 Then cells were fixed and permeabilized as described elsewhere 17 and incubated for 30 minutes at 4°C with PE-conjugated streptavidin. In parallel endocytosis experiments, serum-deprived ST4 cells were incubated in the absence or presence of scalar doses of IGF-1 (from 1 to 100 ng/mL) with unconjugated IFN-␥R2 mAb or isotype-matched mouse IgG1 control mAb as described in "Flow cytometry."…”

“…14 We have reported that in resting and activated human T lymphocytes, IFN-␥R2 expression is prevalently cytoplasmic. 9,13,17 Low surface IFN-␥R2 results from fast, continuous recycling between surface and clathrin-coated vesicles. 17 IFN-␥R2 internalization is not affected in T cells from individuals genetically deficient for IFN-␥R1, 17 in established Th2 clones, 9 and in T-cell lines unable to produce IFN-␥.…”

“…9,13,17 Low surface IFN-␥R2 results from fast, continuous recycling between surface and clathrin-coated vesicles. 17 IFN-␥R2 internalization is not affected in T cells from individuals genetically deficient for IFN-␥R1, 17 in established Th2 clones, 9 and in T-cell lines unable to produce IFN-␥. 13 However, the signals that play a major role in IFN-␥-independent down-regulation of IFN-␥R2 in T cells have not yet been characterized.…”