Passage: A recently advanced theory focuses on abnormalities of the IgA1 molecule. IgA1 is one of the two immunoglobulin subclasses (the other is IgD) that is O-glycosylated on a number of serine and threonine residues in a special proline-rich hinge region. Aberrant glycosylation of IgA appears to lead to polymerisation of the IgA molecules in tissues, especially the glomerular mesangium. A similar mechanism has been claimed to underlie Henoch–Schönlein purpura, a vasculitis that mainly affects children and can feature renal involvement that is almost indistinguishable from IgA nephritis. However, human studies have found that degalactosylation of IgA1 occurs in patients with IgA nephropathy in response only to gut antigen exposures (not systemic), and occurs in healthy people to a lesser extent. This strongly suggests degalactosylation of IgA1 is a result of an underlying phenomenon (abnormal mucosal antigen handling) and not the ultimate cause of IgA nephropathy. Prevailing evidence suggests that both galactose-deficient o-glycans in the hinge region of IgA1 and synthesis and binding of antibodies against IgA1 are required for immunoglobulin complexes to form and accumulate in glomeruli.From the fact that IgAN can recur after renal transplant, it can be postulated that the disease is caused by a problem in the immune system rather than the kidney itself. Remarkably, the IgA1 that accumulates in the kidney does not appear to originate from the mucosa-associated lymphoid tissue (MALT), which is the site of most upper respiratory tract infections, but from the bone marrow. This, too, suggests an immune pathology rather than direct interference by outside agents.

Question: Who is most affected by vasculitis?
children