Store-Operated Ca2+ Entry through ORAI1 Is Critical for T Cell-Mediated Autoimmunity and Allograft Rejection

Abstract

ORAI1 is the pore-forming subunit of the Ca2+ release-activated Ca2+ (CRAC) channel, which is responsible for store-operated Ca2+ entry in lymphocytes. A role for ORAI1 in T cell function in vivo has been inferred from in vitro studies of T cells from human immunodeficient patients with mutations in ORAI1 and Orai1−/− mice, but a detailed analysis of T cell-mediated immune responses in vivo in mice lacking functional ORAI1 has been missing. We therefore generated Orai1 knock-in mice (Orai1KI/KI) expressing a nonfunctional ORAI1-R93W protein. Homozygosity for the equivalent ORAI1-R91W mutation abolishes CRAC channel function in human T cells resulting in severe immunodeficiency. Homozygous Orai1KI/KI mice die neonatally, but Orai1KI/KI fetal liver chimeric mice are viable and show normal lymphocyte development. T and B cells from Orai1KI/KI mice display severely impaired store-operated Ca2+ entry and CRAC channel function resulting in a strongly reduced expression of several key cytokines including IL-2, IL-4, IL-17, IFN-γ, and TNF-α in CD4+ and CD8+ T cells. Cell-mediated immune responses in vivo that depend on Th1, Th2, and Th17 cell function were severely attenuated in ORAI1-deficient mice. Orai1KI/KI mice lacked detectable contact hypersensitivity responses and tolerated skin allografts significantly longer than wild-type mice. In addition, T cells from Orai1KI/KI mice failed to induce colitis in an adoptive transfer model of inflammatory bowel disease. These findings reaffirm the critical role of ORAI1 for T cell function and provide important insights into the in vivo functions of CRAC channels for T cell-mediated immunity.

STIM1 and STIM2 protein deficiency in T lymphocytes underlies development of the exocrine gland autoimmune disease, Sjögren's syndrome

“…Synthesis of IL-2, a critical factor in Treg differentiation and activation, in T cells is dependent on activation of NFAT by SOCE (34). NOD mice, a frequently used mouse model for pSS, display a reduction in IL-2 together with an age-dependent reduction in Treg population and onset of SS (23,24,35).…”

Ion channels in autoimmune neurodegeneration

“…The affected mice show normal lymphocyte development, but T and B cells display severely impaired store-operated Ca 2+ entry and CRAC channel function resulting in strongly reduced expression of several key cytokines [29]. Moreover, genetic deletion of STIM1/2 ameliorates the disease course of EAE [30,31] and a human immunodeficiency syndrome associated with deficiencies in STIM1 function was described recently [32].…”

Physiological and pathophysiological functions of SOCE in the immune system

“…The proliferation of T cells isolated from STIM1-and ORAI1-deficient patients was significantly reduced following in vitro stimulation with anti-CD3, antigens or mitogens (5,29,35,42). This defect in T cell proliferation was also observed in murine lymphocytes lacking both Stim1 and Stim2 genes, but not in murine T cells lacking only Stim1 or Orai1 gene function (Orai1 −/− or Orai1 knock-in (KI) mice, the latter expressing a nonfunctional ORAI1-R93W protein unable to mediate I CRAC ) (16,34,36). Additionally, effector cytokine production by CD4 + T cell subsets was almost completely absent in SOCEdeficient T cells (16,33,34,36,38).…”

“…This defect in T cell proliferation was also observed in murine lymphocytes lacking both Stim1 and Stim2 genes, but not in murine T cells lacking only Stim1 or Orai1 gene function (Orai1 −/− or Orai1 knock-in (KI) mice, the latter expressing a nonfunctional ORAI1-R93W protein unable to mediate I CRAC ) (16,34,36). Additionally, effector cytokine production by CD4 + T cell subsets was almost completely absent in SOCEdeficient T cells (16,33,34,36,38). In accordance with a critical role for SOCE in T cell function not just in vitro but also in vivo, fully MHC mismatched skin allografts from BALB/c mice transplanted onto C57BL/6 mice were tolerated significantly longer by ORAI1-deficient than wildtype mice (36 (54), which is likely due to the significantly impaired effector T cell function in STIM1/STIM2-deficient but not scurfy mice.…”

“…An important role of SOCE in CD8 + T cells and NK cells can be inferred from the susceptibility of human patients with mutations in ORAI1 and STIM1 to severe viral infections (as will be discussed in more detail in chapter 4) (29,35,42,58,59). Similar to CD4 + T cells, SOCE in CD8 + cells is predominantly mediated by STIM1 and ORAI1 following TCR stimulation (36,38,60). CD8 + T cells from patients with mutations in ORAI and STIM1 or STIM1/STIM2-deficient mice lack SOCE and CRAC channel function (16,36,38,61).…”