Type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing β cells in the pancreatic islets, which are essentially mini-organs embedded in exocrine tissue. CTLs are considered to have a predominant role in the autoimmune destruction underlying T1D. Visualization of CTL-mediated killing of β cells would provide new insight into the pathogenesis of T1D, but has been technically challenging to achieve. Here, we report our use of intravital 2-photon imaging in mice to visualize the dynamic behavior of a virally expanded, diabetogenic CTL population in the pancreas at cellular resolution. Following vascular arrest and extravasation, CTLs adopted a random motility pattern throughout the compact exocrine tissue and displayed unimpeded yet nonlinear migration between anatomically nearby islets. Upon antigen encounter within islets, a confined motility pattern was acquired that allowed the CTLs to scan the target cell surface. A minority of infiltrating CTLs subsequently arrested at the β cell junction, while duration of stable CTL–target cell contact was on the order of hours. Slow-rate killing occurred in the sustained local presence of substantial numbers of effector cells. Collectively, these data portray the kinetics of CTL homing to and between antigenic target sites as a stochastic process at the sub-organ level and argue against a dominant influence of chemotactic gradients.
Ken Coppieters, Natalie Amirian, Matthias von Herrath
Response to Pileggi
Type 1 Diabetes Center, The La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
Published February 13, 2012
Although we acknowledge the recent advances by Abdulreda et al, we maintain that their work rather addresses the kinetics of immune responses as they occur at transplantation sites. In our opinion this setting clearly diverges from our setup, which models the behavior of a diabetogenic CTL population in the pancreas. The PNAS paper indeed demonstrates that immune cell subsets can infiltrate the intraocular grafts but only shows similarities to those observed in the subrenal capsular transplantation site and in secondary lymphoid organs. The statement that the ACE approach has 'limit(ed) applicability in studying immune infiltration' therefore applies in the context of modeling T cell infiltration in the pancreas during diabetes development.
The anterior chamber of the eye allows longitudinal, intravital imaging of CTLs to study islet immunobiology
Diabetes Research Institute, University of Miami
Published February 3, 2012
Live microscopy allows acquiring unique dynamic data with cellular resolution shedding light on complex biological processes and cell-cell interactions that are not reproducible ex-vivo. In the January 2012 issue, Coppieters et al. [JCI 2012;122(1):119-131] described the use of intravital imaging of cytotoxic CD8+T-lymphocyte (CTL) killing islet cells in a model of antigen-specific immune responses. They performed live microscopy on surgically exposed murine pancreata expressing a viral glycoprotein in islet beta-cells to study with cellular resolution the pattern of CTL killing in-situ after adoptive transfer of TCR-restricted CD8+ lymphocytes toward the viral protein.
Prior to the publication of their manuscript, our group had reported [PNAS USA 2011;108(31):12863-8; Epub:07/18/2011] an alternative non-surgical approach, i.e., imaging in the anterior chamber of the eye (ACE). Despite the putative 'immune privileged' nature of the ACE, CTL-mediated destruction of intraocular allogeneic islet cells occurs. Immune cell subsets infiltrating the intraocular grafts are similar to those observed in the conventional subrenal capsular transplantation site. Thus, the ACE represents a versatile and valuable experimental tool to study effector immune cell function non-invasively and longitudinally at single-cell resolution in target islet tissue, even in an ectopic extra-pancreatic microenvironment.
Conflict of interest statement: P.-O.B. is one of the founders of the biotech company Biocrine, applying the ACE as an experimental platform. A.C. is on the patent regarding using the ACE as an experimental platform.