Although deposits of complement factors in a kidney biopsy are typical of lupus nephritis, their prognostic relevance had never been investigated until a year ago. Then, around the same time, Kim and colleagues published a study in which deposits were associated with loss of renal function,1 while we published a similar study that reported no such association.2 Here, we explore possible explanations for these seemingly conflicting findings.

Both studies assumed that deposits of C1q with or without C3 in glomeruli reflect activation of the classical pathway and that deposits of C3 without C1q in glomeruli reflect activation of only the alternative pathway of complement. Here, we refer to such patterns of deposits in short as classical and alternative deposits, respectively.

Both studies compared clinical and histopathological characteristics between patients with classical deposits and those with alternative deposits (table 1). Alternative deposits were found in a minority of similar sizes in both studies. In both studies, patients with alternative deposits had less active disease based on higher serum levels of C3 and C4, a lower disease activity index and a lower pathological activity index, …