Frontrunners of T cell activation: Initial, localized Ca ²⁺ signals mediated by NAADP and the type 1 ryanodine receptor

Abstract

The activation of T cells is the fundamental on switch for the adaptive immune system. Ca(2+) signaling is essential for T cell activation and starts as initial, short-lived, localized Ca(2+) signals. The second messenger nicotinic acid adenine dinucleotide phosphate (NAADP) forms rapidly upon T cell activation and stimulates early Ca(2+) signaling. We developed a high-resolution imaging technique using multiple fluorescent Ca(2+) indicator dyes to characterize these early signaling events and investigate the channels involved in NAADP-dependent Ca(2+) signals. In the first seconds of activation of either primary murine T cells or human Jurkat cells with beads coated with an antibody against CD3, we detected Ca(2+) signals with diameters close to the limit of detection and that were close to the activation site at the plasma membrane. In Jurkat cells in which the ryanodine receptor (RyR) was knocked down or in primary T cells from RyR1(-/-) mice, either these early Ca(2+) signals were not detected or the number of signals was markedly reduced. Local Ca(2+) signals observed within 20 ms upon microinjection of Jurkat cells with NAADP were also sensitive to RyR knockdown. In contrast, TRPM2 (transient receptor potential channel, subtype melastatin 2), a potential NAADP target channel, was not required for the formation of initial Ca(2+) signals in primary T cells. Thus, through our high-resolution imaging method, we characterized early Ca(2+) release events in T cells and obtained evidence for the involvement of RyR and NAADP in such signals.

Ca2+ Microdomains in T-Lymphocytes

“…This is also evidenced by recent data showing that knockdown of the three isoforms of RyR (RyR1–3) in T cells largely abolished NAADP-evoked Ca 2+ microdomains (32). Since in T cells further Ca 2+ -mobilizing second messengers, such as IP 3 , are formed, the physiological role of the initial NAADP-dependent Ca 2+ microdomain may be questioned.…”

Nicotinic Acid Adenine Dinucleotide Phosphate Plays a Critical Role in Naive and Effector Murine T Cells but Not Natural Regulatory T Cells

“…Perhaps Ca 2ϩ release in Jurkat cells is less dependent on this trigger. Recent work by Wolf et al (17) confirms a role for the RyR in both Jurkat and primary mouse T cells. However, other sources such as external Ca 2ϩ were found to participate in primary cells.…”

Durable Interactions of T Cells With T Cell Receptor Stimuli in the Absence of a Stable Immunological Synapse

“…(AM) and Fura Red-AM (Wolf et al, 2015). The location of stimulatory spots was recorded using Alexa Fluor 647 conjugated to the stamped anti-CD3.…”