Calcium Signalling Triggered by NAADP in T Cells Determines Cell Shape and Motility During Immune Synapse Formation

Nicotinic acid adenine dinucleotide phosphate (NAADP) has been implicated as an initial Ca²⁺ trigger in T cell Ca²⁺ signalling, but its role in formation of the immune synapse in CD4⁺ effector T cells has not been analysed. CD4⁺ T cells are activated by the interaction with peptide-MHCII complexes on the surface of antigen-presenting cells. Establishing a two-cell system including primary rat CD4⁺ T cells specific for myelin basic protein and rat astrocytes enabled us to mirror this activation process in vitro and to analyse Ca²⁺ signalling, cell shape changes and motility in T cells during formation and maintenance of the immune synapse. After immune synapse formation, T cells showed strong, antigen-dependent increases in free cytosolic calcium concentration ([Ca²⁺] _i ). Analysis of cell shape and motility revealed rounding and immobilization of T cells depending on the amplitude of the Ca²⁺ signal. NAADP-antagonist BZ194 effectively blocked Ca²⁺ signals in T cells evoked by the interaction with antigen-presenting astrocytes. BZ194 reduced the percentage of T cells showing high Ca²⁺ signals thereby supporting the proposed trigger function of NAADP for global Ca²⁺ signalling. Taken together, the NAADP signalling pathway is further confirmed as a promising target for specific pharmacological intervention to modulate T cell activation.