Direct presentation of foreign MHC molecules expressed by donor-derived dendritic cells (DCs) has generally been considered the dominant pathway of allorecognition in acute transplant rejection. However, recent studies implicate preferential activation of the indirect pathway by host DCs. The respective importance of each pathway and the mechanisms that determine their relative contributions remain to be clearly established. In this study, using two-photon microscopy, we visualized host NK cell interactions with syngeneic and allogeneic DCs within intact lymph nodes of mice. Upon contact with allogeneic DCs, NK cells formed prolonged interactions that led directly to target cell lysis. This rapid elimination limited the ability of allogeneic DCs to stimulate primary and recall T cell responses. To discriminate whether donor or host DCs are principally involved in presenting Ag derived from allografts, we used CD11c-diphtheria toxoid receptor mice to conditionally ablate CD11c+ DCs and to show that direct presentation by donor DCs is alone insufficient to elicit acute allograft rejection. We thus propose that rapid elimination of allogeneic DCs limits direct Ag presentation and thereby favors the indirect pathway of alloreactivity.
Dendritic cells (DCs) initiate and polarize adaptive immune responses toward varying functional outcomes. By means of intravital two-photon microscopy, we report that dermal dendritic cells (DDCs) and Langerhans cells (LCs) are differentially mobilized during contact sensitization and by adjuvants such as unmethylated CpG oligonucleotide (CpG) and LPS that induce T helper type 1 (Th1) responses, or papain that induces T helper type 2 (Th2) responses. In ear pinna, contact sensitization, CpG, LPS, and papain all mobilized DDCs in three distinct phases: increased motility and dendritic probing, directed migration, and entry into lymphatic vessels. During the same treatments, the adjacent LCs in ear pinna remained immotile over a 48-hr period of observation. In contrast, footpads lacked DDCs and Th1-polarizing adjuvants selectively induced a delayed mobilization of LCs after 48 hr. Th1 polarization of CD4 + T cells was independent of the immunization site, whereas ear immunization favored Th2 polarization, correlating with sitespecific DC distribution and dynamics. Our results provide an initial description of peripheral DC dynamics in response to adjuvants and imply that LC mobilization enhances a Th1 response and is not sufficient to trigger a Th2 response, whereas mobilization of DDCs alone is sufficient to trigger T-cell proliferation and to polarize initial T-cell activation toward a Th2 response.T-cell priming | two-photon microscopy | vaccine | imaging
Islet cell killing mediated by natural killer cells and T-lymphocytes in diabetes-prone (DP) and diabetic BB rats has been described, but other killing mechanisms may also be involved. Histopathologic studies suggest that macrophages are the first immune cells to infiltrate islets. To determine if macrophages are the first cells mediating islet damage, macrophagemediated cytotoxicity was evaluated in BB rats of different ages. Splenic macrophages isolated from DP rats at 33,100,120, and 140 days of age showed no enhanced islet killing compared with diabetes-resistant rats. Killing at diabetes onset (121 ± 14 days) was markedly increased (43 ± 9.3%) compared with agematched diabetes-resistant controls (19 ± 8.3%, P < .001). Islet inflammation was monitored at all time points. At 120 and 140 days of age, 9 of 11 (82%) DP rats had insulitis, and cytotoxicity was increased in 6 of 11 (55%) rats, which is similar to the number of DP rats that progress to diabetes. At 100 days, 3 of 6 (50%) DP rats again showed diabetic levels of killing, even in the absence of insulitis. These data indicate that 1) islet inflammation is dissociated from clinical diabetes onset, 2) splenic macrophages may have islet-killing potential before islet inflammation, 3) macrophage-mediated islet killing is elevated in all animals immediately after diabetes onset, and 4) macrophages, in addition to natural killer cells and T-lymphocytes, are responsible for cell-mediated islet destruction and thus are candidates for the first cellular effector to result in islet killing. Diabetes 38:1329-31,1989
A decreased acute insulin response to glucose in islet cell antibody positive humans predicts diabetes. Because the dominant mechanism leading to decreased in vivo acute insulin response to glucose remains unclear, perifused islets were examined before and after diabetes onset in BB rats to assess the role of glucose sensitivity on insulin secretion in individual islets. Islets from normal WF rats, diabetes-prone rats without inflamed islets, diabetes-prone rats with inflamed islets, and diabetic rats were studied at 2.0, 8.3, and 16.7 mM glucose. Immunoreactive insulin from WF islets at 16.7 mM glucose was 0.15 +/- 0.02 ng.0-7 min-1 x islet-1 for the first phase and 1.00 +/- 0.05 ng.7-20 min-1 x islet-1 for the second phase of biphasic secretion, compared with basal secretion of 0.10 +/- 0.03 ng.20 min-1 x islet-1 at 2 mM glucose. Diabetes-prone noninflamed islets showed a 0.20 +/- 0.03 ng first-phase secretion, a 1.32 +/- 0.13 ng second-phase secretion after 16.7 mM glucose, and 0.093 +/- 0.02 ng.20 min-1 x islet-1 at 2 mM glucose, indicating no intrinsic BB rat strain secretion abnormality. Diabetes-prone inflamed islets had secretions of 0.35 +/- 0.02 ng during the first phase (P < 0.05 vs. WF) and 1.78 +/- 0.29 ng during the second phase (P < 0.05 vs. WF) after 16.7 mM glucose, with 0.24 +/- 0.08 ng.20 min-1 x islet-1 at 2 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
The store-operated CRAC channels and the store-independent, arachidonic acid-activated ARC channels represent the founding members of a new family of biophysically similar, highly Ca 2þ -selective, Ca 2þ entry channels -the ''Orai channels''. Both of these channels are dependent on STIM1 for their activation, but they differ in the pool of STIM1 responsible. Thus, whereas STIM1 in the ER regulates the CRAC channels on store-depletion, ARC channels are exclusively regulated by the pool of STIM1 that constitutively resides in the PM. Recent studies have shown that the functional CRAC channel pore is formed by a tetrameric arrangement of Orai1 units. In contrast, a heteropentameric assembly of three Orai1 subunits and two Orai3 subunits forms the functional ARC channel pore (Mignen et al. J. Physiol. 587: 4181). Importantly, this inclusion of Orai3 subunits in the channel structure has been shown to play a specific, and unique, role in determining the selectivity of the ARC channels for activation by arachidonic acid. Using an approach based on the generation and expression of various concatenated constructs, we examined the basis for this Orai3-de-
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