Secondary IgA nephropathy.

IgA nephropathy (IgAN) is the most common pattern of primary glomerulonephritis seen in the Western world. In the majority of cases the cause remains unknown. Cases of familial IgAN and secondary IgAN have been reported and these have provided insights into underlying genetic and environmental triggers for this common glomerular disease. Secondary IgAN is seen most commonly in patients with liver disease or mucosal inflammation, in particular affecting the gastrointestinal tract. A number of dietary and microbial antigens have been identified in circulating IgA immune complexes and mesangial IgA deposits, suggesting that environmental factors may play a role in the pathogenesis of IgAN. There is an increasing literature reporting associations between IgAN and other diseases. Whether these reports represent chance associations or genuine shared pathophysiology is discussed.

Human serum IgA1 is substituted with up to six O-glycans as shown by matrix assisted laser desorption ionisation time-of-flight mass spectrometry.

The micro-heterogeneity of human serum IgA1 results from variable O-glycan substitutions in the 'hinge region' of the molecule and this O-glycosylation may be altered in a number of medical conditions. This micro-heterogeneity has been monitored by analysis of IgA1-derived tryptic O-glycopeptides using matrix assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) analysis. With ammonium citrate-trihydroxyacetophenone matrix, individual compositional glycoforms have been baseline resolved in more than 70 samples and these spectra revealed for the first time that, in addition to expected substitution with 3,4 and 5 GalNAcs, a sixth GalNAc substitution was also present in the hinge region of the molecule. The spectra obtained from subsequent exoglycosidase-treated samples confirmed hexa-O-substitution. Following endoprotease digestions of the exoglycosidase treated samples, possible locations for the sixth GalNAc were indicated from further MALDI-ToF-MS analysis. Hexa-substitution accounts for around 5-10% the glycoforms. This is, we believe, the first report of hexa-O-substitution with GalNAc of human serum IgA1.

Infectome: a platform to trace infectious triggers of autoimmunity.

The "exposome" is a term recently used to describe all environmental factors, both exogenous and endogenous, which we are exposed to in a lifetime. It represents an important tool in the study of autoimmunity, complementing classical immunological research tools and cutting-edge genome wide association studies (GWAS). Recently, environmental wide association studies (EWAS) investigated the effect of environment in the development of diseases. Environmental triggers are largely subdivided into infectious and non-infectious agents. In this review, we introduce the concept of the "infectome", which is the part of the exposome referring to the collection of an individual's exposures to infectious agents. The infectome directly relates to geoepidemiological, serological and molecular evidence of the co-occurrence of several infectious agents associated with autoimmune diseases that may provide hints for the triggering factors responsible for the pathogenesis of autoimmunity. We discuss the implications that the investigation of the infectome may have for the understanding of microbial/host interactions in autoimmune diseases with long, pre-clinical phases. It may also contribute to the concept of the human body as a superorganism where the microbiome is part of the whole organism, as can be seen with mitochondria which existed as microbes prior to becoming organelles in eukaryotic cells of multicellular organisms over time. A similar argument can now be made in regard to normal intestinal flora, living in symbiosis within the host. We also provide practical examples as to how we can characterise and measure the totality of a disease-specific infectome, based on the experimental approaches employed from the "immunome" and "microbiome" projects.

Tracing environmental markers of autoimmunity: introducing the infectome.

We recently introduced the concept of the infectome as a means of studying all infectious factors which contribute to the development of autoimmune disease. It forms the infectious part of the exposome, which collates all environmental factors contributing to the development of disease and studies the sum total of burden which leads to the loss of adaptive mechanisms in the body. These studies complement genome-wide association studies, which establish the genetic predisposition to disease. The infectome is a component which spans the whole life and may begin at the earliest stages right up to the time when the first symptoms manifest, and may thus contribute to the understanding of the pathogenesis of autoimmunity at the prodromal/asymptomatic stages. We provide practical examples and research tools as to how we can investigate disease-specific infectomes, using laboratory approaches employed from projects studying the "immunome" and "microbiome". It is envisioned that an understanding of the infectome and the environmental factors that affect it will allow for earlier patient-specific intervention by clinicians, through the possible treatment of infectious agents as well as other compounding factors, and hence slowing or preventing disease development.

Glycoform composition profiling of O-glycopeptides derived from human serum IgA1 by matrix-assisted laser desorption ionization-time of flight-mass spectrometry.

Pools of O-glycopeptides prepared from trypsin-digested reduced and alkylated human serum IgA1 have been analyzed using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-ToF-MS) in the positive-ion mode, using 2,4,6-trihydroxy acetophenone-ammonium citrate matrix. Dozens of such pools prepared from normal serum IgA1 and from serum of patients with a number of different medical conditions have been routinely analyzed in this manner. The glycopeptides present in these pools possess identical amino acid sequences but are substituted with a variety of neutral and sialylated glycans and the spectra obtained were such that individual compositional glycoforms were baseline resolved. In addition, the spectra were reproducible, exhibiting a relative peak intensity and area variation of around 11-16%, enabling the technique to be used for the relative quantitation of the different compositional glycoforms present. This could be achieved manually or by applying a Java program especially developed for this purpose. The MS analysis described here is a major improvement over present MALDI methods used for profiling the O-glycosylation of IgA1. The MS methodology together with the Java data analysis are expected to be generally applicable for profiling O-linked glycopeptides derived from other glycoproteins and probably for N-linked glycopeptide pools.

Immunoglobulin A multiple myeloma presenting with Henoch-Schönlein purpura associated with reduced sialylation of IgA1.

Henoch-Schönlein purpura is characterized by immunoglobulin A1 (IgA1) depositions in blood vessels of the skin or in glomeruli, resulting from altered hinge region O-glycosylation. Henoch-Schönlein purpura is seldom reported as a complication of IgA1 myeloma, even when the circulating IgA concentration is very high. We report two patients with IgA1 myeloma presenting with Henoch-Schönlein purpura. The O-glycosylation of these patients' IgA1 was studied. Both patients showed increased binding to peanut agglutinin lectin, suggesting a low degree of sialylation of the hinge region of IgA1 that was confirmed by mass spectrometry. IgA multiple myeloma, secreting IgA1 molecules with decreased sialylation, presenting with a Henoch-Schönlein purpura-like syndrome was diagnosed.