Insights from prospective, longitudinal studies of individuals at risk for developing type 1 diabetes have demonstrated that the disease is a continuum that progresses sequentially at variable but predictable rates through distinct identifiable stages prior to the onset of symptoms. Stage 1 is defined as the presence of β-cell autoimmunity as evidenced by the presence of two or more islet autoantibodies with normoglycemia and is presymptomatic, stage 2 as the presence of β-cell autoimmunity with dysglycemia and is presymptomatic, and stage 3 as onset of symptomatic disease. Adoption of this staging classification provides a standardized taxonomy for type 1 diabetes and will aid the development of therapies and the design of clinical trials to prevent symptomatic disease, promote precision medicine, and provide a framework for an optimized benefit/risk ratio that will impact regulatory approval, reimbursement, and adoption of interventions in the early stages of type 1 diabetes to prevent symptomatic disease.

Previously it was shown that ␤ 2 -integrins are necessary for slow leukocyte rolling in inflamed venules. In this study, mice that are deficient for either one of the ␤ 2 -integrins, ␣ L ␤ 2 (LFA-1) or ␣ M ␤ 2 (Mac-1), were used to determine which of the

Leukocyte rolling along the walls of inflamed venules precedes their adhesion during inflammation. Rolling leukocytes are thought to arrest by engaging β2 integrins following cellular activation. In vitro studies suggest that chemoattractants may instantaneously activate and arrest rolling leukocytes. However, how leukocytes stop rolling and become adherent in inflamed venules in vivo has remained rather mysterious. In this paper we use a novel method of tracking individual leukocytes through the microcirculation to show that rolling neutrophils become progressively activated while rolling down the venular tree. On average, leukocytes in wild-type mice roll for 86 s (and cover 270 μm) before becoming adherent with an efficiency around 90%. These rolling leukocytes exhibit a gradual β2 integrin-dependent decrease in rolling velocity that correlates with an increase in intracellular free calcium concentration before arrest. Similar tracking analyses in gene-targeted mice demonstrate that the arrest of rolling leukocytes is very rare when β2 integrins are absent or blocked by a mAb. Arrest is ∼50% less efficient in the absence of E-selectin. These data suggest a model of leukocyte recruitment in which β2 integrins play a critical role in stabilizing leukocyte rolling during a protracted cellular activation period before arrest and firm adhesion.

We have previously shown that Mac-1 and LFA-1 play a cooperative role in slow leukocyte rolling in inflamed vessels, and that, although both have a role in leukocyte adhesion, the contribution from LFA-1 exceeds that of Mac-1. In this study, we used mice deficient in ICAM-1 (ICAM-1null) to study the function of ICAM-1 as an endothelial ligand for Mac-1 and LFA-1. The cremaster muscles of these mice were treated with TNF-α and prepared for intravital microscopy. We found that the average rolling velocity in venules was not different in ICAM-1null mice (4.7 μm/s) compared with wild-type mice (5.1 μm/s). Similarly, leukocyte adhesion efficiency in ICAM-1null mice (0.11 ± 0.01 mm) was similar to that in Mac-1−/− (0.12 ± 0.03 mm) mice but significantly increased compared with that in LFA-1−/− (0.08 ± 0.01 mm) mice and significantly reduced from that in wild type (0.26 ± 0.04 mm). When both LFA-1 and ICAM-1 were blocked, rolling velocity increased, and adhesion efficiency and arrest decreased. However, blocking both Mac-1 and ICAM-1 had no greater effect than either blockade alone. We conclude that endothelial ICAM-1 is the main ligand responsible for slow leukocyte rolling mediated by Mac-1, but not LFA-1.