In situ determination of B-cell heavy chain and kappa/lambda light chain expression patterns: Methodology and clinical utility

The authors describe a reverse transcriptase in situ polymerase chain react ion (RT in situ PCR) method that allows the determination of B-cell clonali ty as defined by expression of kappa and lambda mRNA as well as the differe nt VH families that comprise the entire heavy chain (IgH) sequence using pa raffin-embedded, formalin-fixed tissue. Polyclonal expression of B-cell lig ht and heavy chains was documented in two reactive lymph nodes and a spleen in the same histologic distribution as the B-cell marker CD20. Monoclonal expression of kappa versus lambda mRNA was documented in 11 cases of B-cell lymphoma and was corroborated in 5 cases by flow cytometry; each case show ed monoclonal expression of IgH. The authors analyzed seven additional tiss ues where a definitive diagnosis of B-cell lymphoma could not be rendered b ased on histologic, immunohistologic, and clinical analysis. RT in situ PCR for IgH and kappa versus lambda expression differentiated the B-cell lymph omas (n = 2) from reactive B-cell processes (n = 3) and from two cases of B -cell-rich T-cell lymphoma. The described RT in situ PCR methodology allows routine determination of the monoclonal versus multiclonal expression patt erns of B cells, which will facilitate the diagnosis of B-cell lymphomas an d aid in understanding the pathogenesis of B-cell malignancies using archiv al, paraffin-embedded tissues.