TCR Signaling via ZAP-70 Induced by CD3 Stimulation is More Active Under Acidic Conditions

Xin Wang Kenta Hatatani

doi:10.4172/2157-7013.s15-002

Abstract

Although the pH values of blood and tissues are usually maintained in a narrow range around 7.4, some diseased areas, such as cancer nests, inflammatory loci, and infarction areas, are acidified. In the present study, the effect of extracellular acidic pH on TCR signaling was examined with human acute leukemia T cell line Jurkat cells because T cell infiltration is often observed in acidic diseased areas. The phosphorylation levels of CD3-ξ ZAP-70, and PLC-γ1 induced by OKT-3, anti-CD3 antibody, were higher at pH 6.3 than those at pH 7.6. The activation of PLC-γ1 induced by OKT-3 was further increased by the co-stimulation with CD28.6, anti- CD28 antibody, at pH 7.6, but not at pH 6.3. The level of cytosolic free calcium ions was increased to a higher level by the addition of OKT-3 at pH 6.3, compared with that by the addition of OKT-3 plus CD28.6 at pH 7.6. Further addition of CD28.6 decreased the level of cytosolic free calcium ions induced by OKT-3 at pH 6.3. The Ca2+ mobilization was strongly inhibited by BTP2, a potent inhibitor of Ca2+ channels in the plasma membrane, at pH 7.6, while the inhibition was weak at pH 6.3. The Ca2+ mobilization at pH 6.3 was dependent on ZAP-70 and LAT, but not SLP-76. The activation of ERK and p38 increased as pH decreased. No activation of ERK2 in the presence of OKT-3 was observed in the Jurkat mutant deficient in ZAP-70 at pH 6.3, while ERK1 was activated by the addition of OKT-3 in this mutant. The expression of IL-2 was not induced by OKT-3 or OKT-3 plus CD28.6 at pH 6.3. These results suggest that the TCR signaling initiated by CD3 stimulation is more active at acidic pH in Jurkat cells and its pathway is different in parts under different pH conditions.

Highlights

Alterations in the microenvironments at the sites of infection and inflammation have been studied since the 1940s
The phosphorylations of CD3-ξ and ZAP-70 were further examined with the addition of OKT-3, the stimulator of T cell antigen receptor (TCR) signaling
No p38 activation was observed in the P116 cells at pH 7.6 or 6.3 regardless of the presence or absence of OKT-3. These results suggest that the TCR signaling pathway that activates ERK1/2 and p38 is dependent on ZAP-70 and is more active at acidic pH

Summary

Introduction

Alterations in the microenvironments at the sites of infection and inflammation have been studied since the 1940s. The different signaling pathways have been investigated under different pH conditions in Jurkat T cells [17] and the phosphorylation levels of p38 and ERK were elevated at acidic pH [18]. These previous studies support the notion that acidic extracellular environments exert a great influence on immune response. It is still unclear how extracellular low pH affects TCR signaling, especially Ca2+ mobilization

Methods

Results

Conclusion