Experimental allergic encephalomyelitis (EAE) is induced by T cell-mediated immunity to central nervous system antigens. In H-2u mice, EAE is mediated primarily by T cells specific for residues 1-11 of myelin basic protein (MBP). We demonstrate that differential tolerance to MBP1-11 versus epitopes in MBP121-150 is induced by expression of endogenous MBP, reflecting extreme differences in stability of peptide/MHC complexes. The diverse MBP121-150-specific TCR repertoire can be divided into three fine specificity groups. Two groups were identified in wild-type mice despite extensive tolerance, but the third group was not detected. Activated MBP121-150-specific T cells induce EAE in wild-type mice. Thus, encephalitogenic T cells that escape tolerance either recognize short-lived peptide/MHC complexes or express TCRs with unique specificities for stable complexes.

The frequency of primary failure in arteriovenous fistulas (AVFs) remains unacceptably high. This lack of improvement is due in part to a poor understanding of the pathobiology underlying AVF nonmaturation. This observational study quantified the progression of three vascular features, medial fibrosis, intimal hyperplasia (IH), and collagen fiber organization, during early AVF remodeling and evaluated the associations thereof with AVF nonmaturation. We obtained venous samples from patients undergoing two-stage upper-arm AVF surgeries at a single center, including intraoperative veins at the first-stage access creation surgery and AVFs at the second-stage transposition procedure. Paired venous samples from both stages were used to evaluate change in these vascular features after anastomosis. Anatomic nonmaturation (AVF diameter never ≥6 mm) occurred in 39 of 161 (24%) patients. Neither preexisting fibrosis nor IH predicted AVF outcomes. Postoperative medial fibrosis associated with nonmaturation (odds ratio [OR], 1.55; 95% confidence interval [95% CI], 1.05 to 2.30; =0.03, per 10% absolute increase in fibrosis), whereas postoperative IH only associated with failure in those individuals with medial fibrosis over the population's median value (OR, 2.63; 95% CI, 1.07 to 6.46;=0.04, per increase of 1 in the intima/media ratio). Analysis of postoperative medial collagen organization revealed that circumferential alignment of fibers around the lumen associated with AVF nonmaturation (OR, 1.38; 95% CI, 1.03 to 1.84; =0.03, per 10° increase in angle). This study demonstrates that excessive fibrotic remodeling of the vein after AVF creation is an important risk factor for nonmaturation and that high medial fibrosis determines the stenotic potential of IH.

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This preliminary study indicates that postoperative intimal hyperplasia by itself is not associated with the development of focal venous stenosis in 2-stage fistulas.

Background and objectives: The venous vasa vasorum is the mesh of microvessels that provide oxygen and nutrients to the walls of large veins. Whether changes to the vasa vasorum have any effects on human arteriovenous fistula outcomes remains undetermined. In this study, we challenged the hypothesis that inadequate vascularization of the arteriovenous fistula wall is associated with maturation failure. Design, setting, participants, and measurements: This case–control pilot study includes pre-access veins and arteriovenous fistula venous samples (i.e. tissue pairs) from 30 patients undergoing two-stage arteriovenous fistula creation (15 matured and 15 failed to mature). Using anti-CD31 immunohistochemistry, we quantified vasa vasorum density and luminal area (vasa vasorum area) in the intima, media, and adventitia of pre-access veins and fistulas. We evaluated the association of pre-existing and postoperative arteriovenous fistula vascularization with maturation failure and with postoperative morphometry. Results: Vascularization of veins and arteriovenous fistulas was predominantly observed in the outer media and adventitia. Only the size of the microvasculature (vasa vasorum area), but not the number of vessels (vasa vasorum density), increased after arteriovenous fistula creation in the adventitia (median vasa vasorum area 1366 µm2/mm2 (interquartile range 495–2582) in veins versus 3077 µm2/mm2 (1812–5323) in arteriovenous fistulas, p < 0.001), while no changes were observed in the intima and media. Postoperative intimal thickness correlated with lower vascularization of the media ( r 0.53, p = 0.003 for vasa vasorum density and r 0.37, p = 0.045 for vasa vasorum area). However, there were no significant differences in pre-existing, postoperative, or longitudinal change in vascularization between arteriovenous fistulas with distinct maturation outcomes. Conclusion: The lack of change in intimal and medial vascularization after arteriovenous fistula creation argues against higher oxygen demand in the inner walls of the fistula during the vein to arteriovenous fistula transformation. Postoperative intimal hyperplasia in the arteriovenous fistula wall appears to thrive under hypoxic conditions. Vasa vasorum density and area by themselves are not predictive of maturation outcomes.

The combination of genetic and environmental factors that contribute to human autoimmune responses has made potential triggers of these diseases difficult to identify. We examined how experimental allergic encephalomyelitis (EAE), an animal model of multiple sclerosis, is triggered using TCR-transgenic mice specific for myelin basic protein (MBP). In these TCR-transgenic mice, EAE can be actively induced and also occurs spontaneously. The incidence of spontaneous EAE in this model is largely confined to adolescence and early adulthood and is more prevalent among males than females, indicating that hormonal influences may contribute to triggering central nervous system autoimmune disease. Disease induction studies show that not all stimuli that activate MBP-specific T cells in vivo also induce EAE. Immunization with MBP peptide stimulates the transgenic T cells to produce Th1 cytokines; however, the activated T cells do not accumulate in the central nervous system and induce EAE unless pertussis toxin is also administered. EAE can be induced by intrathecal injection of either stimulated or nonstimulated transgenic T cells into nontransgenic or transgenic recipients. Therefore, gaining access to the central nervous system appears to be the critical step in this model for the induction of EAE, regardless of the activation state of the T cells.

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