T Cell Autocrine Hyaluronan Forms Complex Structures in CD4 T Cell Cytoplasm and Plays a Critical Role in Formation of the Immune Synapse

SummaryThis study examines the involvement of T cell autocrine hyaluronan (HA) with the immunological synapse (IS) that mediates T cell activation by antigen-presenting cells (APCs). Three-dimensional (3D) confocal images of mouse CD4⁺ T cells interacting with B cell lymphoma (A20) APCs in vitro showed HA to be primarily on the T cell side of the IS, appearing as a compact mass indenting the T cell nucleus. Similar 3D imaging of CD4⁺ T cells forming a pseudo-IS on anti-CD3 antibody-coated glass showed HA in the vicinity of the IS in dense masses or complex, arched, columnar structures. Affinity/immunofluorescence labeling studies confirmed the HA masses and columns were cytoplasmic, located beneath the cortical actin layer but outside the nucleus. In T cells forming a pseudo-IS, the HA-binding protein RHAMM was localized to cortical cytoplasm and had limited spatial overlap with cytoplasmic HA. Pre-exposure of T cells to the HA synthesis inhibitor 4-methylumbelliferone (4-MU) or to the HA-binding peptide Pep-1 inhibited IS formation with A20 APCs. Moreover, actin ring development in T cell pseudo-IS was inhibited by pre-exposure to 4-MU, but not by pre-exposure to Pep-1. Collectively, our previous and present studies suggest a complex role for cell surface and cytoplasmic T cell autocrine HA in IS formation and T cell receptor signaling.