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Two-photon microscopy of T cell activation

Activation of T cells is at the centre of immune response development. The INVIVO TCELL IMAGING project analysed the role of isoforms of phosphoinositide-3-kinase (PI3K) in this process.
Two-photon microscopy of T cell activation
Interactions between dendritic cells (DCs) and T cells play a central role during the induction of an immune response and in immunological tolerance. DCs are specialised cells that capture antigens in peripheral tissues and migrate to draining peripheral lymph nodes (PLNs), where they present peptide-MHC (pMHC) complexes to naive T cells. The goal of the EU-funded two-year INVIVO TCELL IMAGING project was to elucidate the contribution of an isoform of the PI3K family of enzymes to T cell activation.

PI3Ks are a family of related intracellular signal transducer enzymes. They are involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which in turn are involved in cancer.

The best characterised PI3K isoform in T cell receptor signalling is the PI3K delta or p110delta. As a model, researchers used mice carrying a target mutation in the catalytic domain of p110delta. In these mice, p110delta lipid kinase activity was completely abrogated, with no alteration in kinase activities of p110alpha and p110beta. They used an in vivo two-photon microscopy (2PM) imaging technique in combination with inflammatory models, flow cytometry and other techniques to investigate the role of p110delta in CD4+ T cell activation.

Researchers investigated the downstream effects of T cells activated in the presence or absence of functional p110δ. This analysis was done in a mouse arthritis model. Animals were immunised by subcutaneous injection with methylated bovine serum albumin (mBSA) and ovalbumin (OVA) emulsified in complete Freund's adjuvant. Arthritis was induced by injecting mBSA and OVA into the left knee joint, while PBS was injected into the right knee joint as a control.

Animals were analysed at various time points after the induction of arthritis. The histology results showed a massive cell infiltrate into the joints of mice and such inflammation persevered in the presence of wild-type T cells. Data showed a massive neutrophil recruitment already at day 1, with monocytes arriving at day 3 and persisting up to day 14. During arthritis onset, the p110delta mutant T cell population was completely eradicated from the lymph nodes, as well as from the peri-articular tissue.

In summary, project generated data presented comprehensive molecular analysis of the inflammatory action of p110delta.

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