Polymerase chain reaction (PCR)-based analysis for detecting
immunoglobulin heavy chain gene (IgH) rearrangements in
lymphoproliferative disorders is well established. The presence of one or two discrete bands is interpreted as a monoclonal proliferation, whereas a smear pattern represents a polyclonal population. Prompted by our observation of discrete bands in histologically reactive processes with a relative paucity of B cells, we sought to determine whether low numbers of B cells in biopsy specimens could artifactually produce pseudomonoclonal bands. We performed IgH PCR analysis on serially diluted
DNA samples from 5 B cell non-Hodgkin's
lymphomas (B-NHLs), 5 reactive lymph nodes, 5 reactive tonsils and 10 microdissected germinal centers from a lymph node with follicular
hyperplasia. We also assessed multiple aliquots of
DNA samples from small biopsy specimens of reactive lymphocytic processes from the stomach (5 cases). PCR products were evaluated using high resolution
agarose or
polyacrylamide gels, and
DNA sequencing was performed on IgH PCR products from two reactive germinal centers, which yielded monoclonal bands of identical size. All 5 B-NHLs harboring monoclonal B cell populations yielded single discrete bands, which were maintained in all dilutions. By contrast, all of the reactive lesions with polyclonal patterns at 50 ng/microl starting template concentration showed strong pseudomonoclonal bands at dilutions of 1:1,000 to 1:1,500 in placental
DNA. Two of the microdissected reactive germinal centers that showed bands of identical size on duplicate reactions were proven to have different IgH sequences by sequencing. We conclude that specimens containing low numbers of polyclonal B cells may produce pseudomonoclonal bands on IgH PCR analysis. IgH PCR analysis should be performed on multiple aliquots of each
DNA sample, and only samples that yield reproducible bands of identical size can be reliably interpreted as monoclonal.