IgA nephropathy is the most common GN in the world. Does IgA molecule in this disease have a light chain predominance? Yes it does.
In early 1990s, Lai K ( 30 patients) et al evaluated this concept. Compared to kappa staining, the lambda staining was higher in IgA nephritic patients and in addition there was pre dominance of IgA lambda chains in circulation. Interestingly the same authors published the same results in AJKD in 1998 showing the same concept. In the same year, the same group of authors showed that IgA had strong lambda mesangial binding in another journal. Interestingly, a JASN review later refers to the Lai studies as well regarding the lambda dominance of IgA.
A more thorough study done recently is more intriguing. The pattern of light chain IF and light microscopic diagnosis in 306 cases of various nephropathies was reviewed in one center in India. Light chain deposits were seen in 240 (78.43%) cases. In IgA nephropathy, lupus nephritis and post-infectious glomerulonephritis (PIGN), lambda positivity was more as compared to kappa. Light chain deposits in LCDD and membranous nephropathy were more kappa type.
In other words, there is some lambda predominance of kappa in IgA nephropathy but we have to keep in mind the number of patients that the first 1990s this was evaluated in. It was interesting to see that the retrospective review confirmed this from India and it also showed that PIGN and lupus also had a more lambda predominance. There is also IgA myeloma which is important to keep in the differential if the pathologist says there is significant more dominance( but the light microscopy and EM findings will be much different in myeloma related disease)