A Critical Temporal Window for Selectin-dependent CD4+ Lymphocyte Homing and Initiation of Late-Phase Inflammation in Contact Sensitivity

Abstract

Contact sensitivity (CS) is an inflammatory disorder characterized by early and late phases of leukocyte recruitment. We used a noninvasive intravital microscopy technique allowing for the direct visualization of leukocyte rolling and adhesion on blood vessel endothelium. By blocking specific adhesion molecules, we elucidated the molecular mechanisms mediating early leukocyte recruitment to be E- and P-selectin and demonstrated that leukocyte recruitment in the late phase had a different adhesive profile (mainly α4-integrin). Complete blockade of E- and P-selectin within the first 2 h of leukocyte–endothelial cell interactions (but not later) eliminated selectin-independent leukocyte recruitment at 24 h. Despite the predominance of neutrophils in the early phase, specific elimination of CD4+ lymphocytes in the early phase eliminated the late response. CD4+ lymphocytes homed to skin via E- and P-selectin within the early phase and induced the late phase response. Addition of these same CD4+ lymphocytes 2 h after antigen challenge was too late for these cells to home to the skin and induce late phase responses. Our data clearly demonstrate that the antigen-challenged microenvironment is only accessible to CD4+ lymphocytes for the first 2 h, and that this process is essential for the subsequent recruitment of other leukocyte populations in late phase responses.

Endogenous Regulatory T Cells Adhere in Inflamed Dermal Vessels via ICAM-1: Association with Regulation of Effector Leukocyte Adhesion

“…Using rhodamine 6G to stain all leukocytes, we found that in sensitized mice challenged once with oxazolone, adhesion followed an extended time course, peaking 8-24 h after challenge before returning to near basal levels by 48 h (Fig. 1A), observations consistent with previous findings (35,39). In contrast, after a second challenge, leukocyte adhesion peaked sharply at 4 h and then rapidly declined such that by 8 h, adhesion had returned to basal levels, where it remained over the subsequent 40 h (Fig.…”

“…Administration of anti-CD4 resulted in ∼90% depletion of both intravascular and extravascular CD4 + cells within 24 h, that is, prior to initiation of the second challenge (data not shown). In mice treated in this manner, we observed a robust neutrophil adhesion response in the second challenge, consistent with our previous findings that the critical "pioneer" CD4 + effector T cells required for initiation of the CS response enter the skin within the first 2 h after the initial challenge (39). Examination of the dermal microvasculature in CD4-depleted mice demonstrated a significant, 5-fold increase in adhesion of CD8 + T cells during the second challenge, relative to nondepleted (isotype control) mice (Fig.…”

CD4+CD25+ regulatory T cells suppress contact hypersensitivity reactions by blocking influx of effector T cells into inflamed tissue

“…The final magnitude of the inflammatory reaction is further correlated with the efficiencyof leukocyterecruitmentintheearlyphase [16], and thus, rapid blockade of leukocyte adherence by Treg is crucial for efficient reduction of the CHS response.…”

The Biophysics of T Lymphocyte Activation In Vitro and In Vivo

“…Another important function of helper cells is to support the generation of cytotoxic effector cells. Consequently, a part of the pre-activated CD4 + T cell will march towards the lymph node's B cell zone [32], while others stay in the T cell zone or leave the lymph node to function in the periphery [38]. A CD8 + cell, in contrast, would turn into a cytotoxic T cell (CTL) possessing various direct and indirect possibilities of killing infected cells.…”

“…Key factors that collectively determine the homing of leukocytes are interactions between integrins or selectins with their tissue adhesion molecules as well as interactions between chemokine receptors and their specific ligands, the chemokines [13,[35][36][37]. In addition, the presence of inflammatory stimuli modulates the homing behavior of immune cells [38]. Activated T cells start homing to peripheral tissues where they exert pro-inflammatory regulatory effector functions or recirculate as memory cells [39].…”