Peter J.C. van Breda Vriesman

The role of nasopharyngeal lymphoid tissue

Nasal-associated lymphoid tissue (NALT), which comprises paired lymphoid organs in the nasopharynx of rodents, is the principal mucosal lymphoid tissue of the respiratory tract. As described in this review, NALT bears certain similarities to the Peyers patches of the intestine but the two differ remarkably in morphology, lymphoid migration patterns and the binding properties of their high endothelial venules (HEV).

Thin-Basement-Membrane Nephropathy in Adults with Persistent Hematuria

Thin-basement-membrane nephropathy, also called benign recurrent hematuria, is characterized by diffuse thinning of the glomerular basement membrane and by hematuria. To determine the incidence of thin-basement-membrane nephropathy among patients with idiopathic hematuria, we conducted a prospective study in the nephrology units of three large hospitals in the Netherlands. Eighty normotensive adults without azotemia underwent renal biopsy because of recurrent macroscopic hematuria (n = 26) or persistent microscopic hematuria (n = 54). Idiopathic IgA nephropathy was found in 27 of the 80 patients. Light microscopical examination showed that 42 patients had normal renal tissue. The remaining 11 patients had mesangioproliferative glomerulonephritis (n = 5), interstitial nephritis (n = 3), or focal global glomerulosclerosis (n = 3). Tissue from the 42 patients whose renal biopsy specimens were normal when examined with light microscopy was analyzed morphometrically with electron microscopy to determine the thickness of the glomerular basement membrane. Two subsets of patients were identified by this analysis. In 18, thin-basement-membrane nephropathy was found (mean basement-membrane thickness [+/- SE], 191 +/- 28 nm; normal, 350 +/- 43 nm); all but one of these 18 patients had microscopic hematuria, which persisted during follow-up (median duration, 50 months). (Of the 54 patients who presented with microscopic hematuria, 17 [31 percent] had thin-basement-membrane nephropathy.) The thickness of the glomerular basement membrane was normal in the other 24 patients (361 +/- 69 nm); during follow-up, hematuria disappeared in all 13 of these patients who had macroscopic hematuria, and hematuria resolved in 5 of the 11 patients who had microscopic hematuria. We conclude that in patients with persistent microscopic hematuria, the incidence of thin-basement-membrane nephropathy is similar to that of idiopathic IgA nephropathy. Morphometric analysis of the thickness of the glomerular basement membrane should be included in the workup of adults with persistent microscopic hematuria that is not of urologic origin.

Improved outcome in anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis: a 30-year follow-up study

BACKGROUND Anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis has a poor prognosis. In the current study, we assessed whether prognosis in these patients improved over the last three decades. METHODS In a large inception cohort, all consecutive patients with ANCA-associated glomerulonephritis were included between January 1979 and December 2009. Inclusion criteria were the presence of ANCA and the availability of a kidney biopsy. To assess renal and patient survival, patients were divided in three groups through time: 1979-89, 1990-2000 and 2001-09. RESULTS A total of 181 patients were included. One-, 5- and 10-year survival was 77, 66 and 49%, respectively. Survival within the time groups was significantly different, yielding a hazard ratio for death of 2.9 for 1990-2000 and 3.9 for 1979-89 compared with 2001-09 (P < 0.001). Serum creatinine and active lesions as found in the kidney biopsy significantly decreased through the three decades. CONCLUSIONS Both patient and renal survival in patients with ANCA-associated renal vasculitis have improved over the last three decades. We postulate that both earlier diagnosis and better therapeutic management of patients are responsible for this effect.

Estimating Renal Survival Using the ANCA-Associated GN Classification

A histopathological classification system for ANCA-associated vasculitis was recently published, but whether this system predicts renal outcome requires validation. Here, we analyzed data from 164 consecutive patients with biopsy-proven renal involvement of ANCA-associated vasculitis. The ANCA-associated GN (AGN) classification categorizes patients as having focal, mixed, crescentic, or sclerotic GN. Five-year renal survival rates by categories of the AGN classification scheme were 91% for focal, 69% for mixed, and 64% for crescentic (log-rank P<0.0001). Only one patient was classified as sclerotic. Furthermore, the percentage of normal glomeruli found on biopsy estimated renal survival with the same precision as did the AGN classification scheme. Patients classified as crescentic or mixed, however, had worse survival when the percentage of normal glomeruli was <25%. In conclusion, the AGN classification for renal biopsy specimens is a practical and informative scheme with which to categorize patients with ANCA-associated vasculitis, but adding the percentage of normal glomeruli to the system seems to improve its predictive value.

Essential role of TGF‐β in the natural resistance to experimental allergic encephalomyelitis in rats

Experimental allergic encephalomyelitis (EAE) is a T cell‐mediated autoimmune disease induced in susceptible rat strains by a single immunization with myelin basic protein (MBP). The Lewis (LEW) strain is susceptible to disease induction while the Brown Norway (BN) strain is resistant. This resistance involves non‐MHC genes since congenic BN‐1L rats, with LEW MHC on a BN‐derived background, are also resistant. In the present study we show that, upon immunization with MBP, the non‐MHC‐encoded resistance to develop clinical EAE in BN‐1L rats is associated with a decreased production of IFN‐γ. This may be due to a difference between LEW and BN‐1L rats in their ability to produce regulatory cytokines such as IL‐4, IL‐10 and TGF‐β. In comparison to LEW rats, immune lymph node cells from BN‐1L rats express an increased amount of IL‐4 mRNA but produce less IL‐10. Furthermore, the sera from BN‐1L rats contain higher amounts of active TGF‐β1. Therefore, we have investigated the involvement of IL‐4 and TGF‐β in the resistance of BN‐1L rats to develop EAE using neutralizing mAb. Neutralization of TGF‐β, but not IL‐4, renders BN‐1L rats susceptible to clinical EAEwithout affecting the proliferation or the cytokine repertoire of immune lymph node cells. With respect to the origin of the endogenous TGF‐β production, we excluded the involvement of CD8 T cells and discuss a possible role of platelets and of CD4 T cells exhibiting the CD45RClow phenotype.

MYASTHENIA GRAVIS AS A PROTOTYPE AUTOIMMUNE RECEPTOR DISEASE

Myasthenia gravis (MG) is an organ-specific autoimmune disease in which autoantibodies against nicotinic acetylcholine receptors (AChR) at the postsynaptic membrane cause loss of functional AChR and disturbed neuromuscular transmission. The immunopathogenic mechanisms responsible for loss of functional AChR include antigenic modulation by anti-AChR antibodies, complement-mediated focal lysis of the postsynaptic membrane, and direct interference with binding of acetylcholine to the AChR or with ion channel function. The loss of AChR and subsequent defective neuromuscular transmission is accompanied by increased expression of the different AChR subunit genes, suggesting a role for the target organ itself in determining susceptibility and severity of disease. Experimental autoimmune myasthenia gravis (EAMG) is an animal model for the disease MG, and is very suitable to study the immunopathogenic mechanisms leading to AChR loss and the response of the AChR to this attack. In this article the current concepts of the structure and function of the AChR and the immunopathological mechanisms in MG and EAMG are reviewed.

The CD8 T Cell Compartment Plays a Dominant Role in the Deficiency of Brown-Norway Rats to Mount a Proper Type 1 Immune Response

Differential cytokine production by T cells plays an important role in regulating the nature of an immune response. In the rat, Brown-Norway (BN) and Lewis (LEW) strains differ markedly in their susceptibility to develop either type 1 or type 2-mediated autoimmune manifestations. BN rats are susceptible to type 2-dependent systemic autoimmunity, while LEW rats are resistant. Conversely, type 1-mediated, organ-specific autoimmune disease can be easily induced in LEW, but not in BN, rats. The mechanisms involved in the differential development of type 1 and type 2 immune responses by these two strains are still unknown. In the present study we analyzed the contributions of APC, CD4 and CD8 T cells, and MHC molecules in the difference between LEW and BN rats to develop a type 1 immune response. First, we show that the defect of BN T cells to produce type 1 cytokines in vitro does not require the presence of APC and, by using an APC-independent stimulation assay, we have localized the defect within the T cell compartment. Both CD4 and CD8 T cells are involved in the defect of BN rats to develop a type 1 immune response with a major contribution of the CD8 T cell compartment. This defect is associated with an increase in the type 2 cytokine IL-4 in both BN T cell populations, but neutralization of this cytokine does not restore this defect. Finally, by using MHC congenic rats, we show that the MHC haplotype is not involved in the defect of BN T cells to mount a proper type 1 cytokine response.

Age-related susceptibility to experimental autoimmune myasthenia gravis : Immunological and electrophysiological aspects

Susceptibility to experimental autoimmune myasthenia gravis (EAMG) was found to decrease with aging in both Lewis and Brown Norway (BN) rats. In this study, the difference in susceptibility between young and aged Lewis and BN rats was used to analyze factors determining the clinical severity of EAMG. The incidence and severity of muscular weakness did not correlate with acetylcholine receptor (AChR) loss nor with the ability of antibodies to interfere with AChR function. Aged rats showed significantly lower anti‐rat AChR antibody titers than young rats and developed less severe or no clinical signs of disease. In individual young or aged rats, however, no significant correlation was found between the clinical signs of disease and anti‐rat AChR titer. Neuromuscular transmission was found to change with aging as measured by single‐fiber electromyography (SFEMG). In aged BN rats, increased jitter and blockings were found even before EAMG induction. Despite this disturbed neuromuscular transmission, these aged BN rats were clinically resistant against induction of EAMG. The results of this study indicate that the age‐related susceptibility to EAMG is influenced by factors determined by the immune attack as well as mechanisms at the level of the neuromuscular junction.

Differential effects of X-irradiation and cyclosporin-A administration on the thymus with respect to the generation of cyclosporin-A-induced autoimmunity.

Cyclosporin A (CsA), a potent inhibitor of T-cell activation, has been shown to have several effects on thymocyte maturation, thymic stromal cells, and the generation of autoreactive T cells. In Lewis rats, the combination of lethal irradiation, syngeneic bone marrow transplantation, and a 4-week course of CsA administration causes the development of an autoimmune disease (CsA-AI) resembling allogeneic graft-versus-host disease. This occurs upon withdrawal of CsA, provided the thymus receives irradiation and is present during CsA treatment. In this study, the separate effects of irradiation or CsA treatment on thymic stromal cells and thymocytes, compared to the combinatory effects, were examined using immunohistochemistry and tricolor flow cytometric analysis. CsA treatment causes an involution of the thymic medulla and a strong reduction of the cell number of thymocytes and stromal cells residing in the medulla. However, within the remaining medullary area, changes in cell distribution and antigen density on these cells were not observed. Irradiation on the other hand causes a strong depletion of thymocytes. The thymocyte population is recovered within 2 weeks and a cortical and medullary region can be distinguished. CsA treatment in combination with irradiation results in a strongly inhibited recovery of the medulla during CsA treatment, whereas the cortex recovers to normal size and morphology. The presence of the medullary IDC and epithelial cells is reduced proportionally to the small size of the medulla. However, the distribution of these stromal cells is normal. During the CsA administration, the thymuses from irradiated and CsA-treated rats are very similar to thymuses from CsA-treated rats. In conclusion, no changes specific for irradiation plus CsA treatment have been observed. Regarding the distribution and size of medullary stromal cells and residing thymocytes, thymuses from irradiated and CsA-treated rats hardly differ from the thymuses from rats treated only with CsA. Therefore, irradiation seems essential in the generation of CsA-AI by eliminating suppressor-cell circuits in the periphery.

Complement in ANCA-associated glomerulonephritis

Background Anti-neutrophil cytoplasmic antibodies (ANCA) are found in pauci-immune necrotizing crescentic glomerulonephritis. In the past, the role of complement in ANCA-associated vasculitis (AAV) was assumed to be minimal. More recently, however, it was found that blocking the complement cascade in a mouse model of AAV reduces glomerular damage. Immune complex deposits have been found in biopsies from AAV patients. In this study, we questioned whether immune complex formation or deposition may result in complement activation in ANCA-associated glomerulonephritis. Methods ANCA-positive patients from the Limburg Renal Registry were included between 1979 and 2011. Renal histology was documented together with immunoglobulin and complement immunofluorescence. In addition, C3d, properdin, C4d and mannose-binding lectin (MBL) were stained. Electron microscopy was performed. Circulating immune complexes were determined in a subset of patients, as well as C3 allotypes. Results C3c was found in 78 of 187 renal biopsies (41.7%) divided over 32.3% of proteinase-3 (PR3)-AAV patients and 52.3% of myeloperoxidase (MPO)-AAV patients (P = 0.006), whereas C3d was found positive in 51.1% of PR3-AAV patients and 70.4% of MPO-AAV patients (P = 0.105). C4d was found positive in 70.8%, properdin in 38.7% and MBL in 30.4% of patients. Whereas C4d and MBL positivity was similar between the AGN groups, properdin was more common in biopsies classified as crescentic compared with biopsies classified as focal or mixed. Renal biopsies positive for C3d and/or properdin showed more cellular crescents and less normal glomeruli compared with biopsies negative for C3d and/or properdin (P < 0.05). In 3 out of 43 renal biopsies analysed by electron microscopy, small electron dense deposits were found. In 14 of 46 patients analysed, circulating immune complexes were detectable. No association between histological findings and C3 allotypes was found. Conclusions In the majority of AAV patients, no immune complex deposits were found in their renal biopsies. C3d, C4d and C5b-9 staining, however, was found to be positive in a majority of analysed renal biopsies. Importantly, C3d and properdin staining was associated with cellular crescents. We hypothesize that local immune complexes are quickly degraded in AAV and therefore not visible by electron microscopy. Our findings are compatible with the hypothesis that complement activation in AAV occurs predominantly via alternative pathway activation.