Abstract
A deeper understanding of the mechanism of complement activation may help to elucidate the pathogenesis of IgA nephropathy (IgAN). Traditionally, the activation of an alternative pathway (AP) has been recognized as an enhancer mechanism of glomerular damage. This paper documents contemporary information concerning the possible pathological mechanisms of the lectin pathway (LP) in the circulation and in the glomerulus. The circulating initiator of LP activation is not fully understood. However, ligands for mannose-binding lectin (MBL) which are among the starter molecules of the LP are aberrant glycosylated molecules-containing immune complex. Recent reports have focused on N-glycans on secretory IgA as a candidate ligand. Mesangial deposits of MBL are seen in 25% of patients with IgAN. Mesangial deposits of MBL and C4 and/or C4 breakdown products are implicated as markers for disease progression of IgAN. On the other hand, patients with MBL deficiency tend to show better clinical presentation and lower levels of urinary protein and serum creatinine than MBL-sufficient patients. It is now recognized that involvement of AP and LP constitutes an additional mechanism for explaining the progression of IgAN.
Highlights
IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis
Since other complement molecules, such as properdin and C5, are colocated in the mesangial areas with IgA, but C1q is absent and there is an increase of C3 breakdown products in the serum of patients with IgAN, we had recognized that alternative pathway (AP) activation is involved in the pathogenesis of IgAN [5]
After discovering new molecules which belong to the lectin pathway (LP), we came to believe there is accumulating evidence to support a hypothesis of the occurrence of LP activation in the pathogenesis of IgAN
Summary
IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis. It is generally agreed that up to 30% of patients with IgAN eventually progress to endstage kidney disease [1]. Since other complement molecules, such as properdin and C5, are colocated in the mesangial areas with IgA, but C1q is absent and there is an increase of C3 breakdown products in the serum of patients with IgAN, we had recognized that alternative pathway (AP) activation is involved in the pathogenesis of IgAN [5]. After discovering new molecules which belong to the lectin pathway (LP), we came to believe there is accumulating evidence to support a hypothesis of the occurrence of LP activation in the pathogenesis of IgAN. The issues surrounding these scenarios with LP activation are reviewed to summarize their potential significance in the pathogenesis of IgAN. In order to explain the updated knowledge in plain terms, the main body was separated into three parts, “In circulation,” “ In kidney,” and “Infection and clinical course.”
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