An immunohistological study of reactive lymphoid tissue

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Abstract
A study was performed to document the patterns of cytoplasmic Ig H and L chain expression in reactive [human] lymphoid tissue, using single and double immunoenzymatic labeling techniques. The investigation was undertaken to provide information on whether the normal counterparts of high grade lymphoma cells (e.g., centroblasts, immunoblasts) ever express > 1 L or H chain (as noted in the past for lymphomas), and to seek evidence of intraclonal switching from cytoplasmic IgM to cytoplasmic IgG expression. Paraffin embedded sections, all showing substantial reactive changes, were analyzed by immunoperoxidase stains for the 3 major Ig classes (IgG, IgM and IgA), both L chain classes and J chains. Double immunoenzymatic labeling techniques were used to search for cells showing simultaneous expression of .kappa. and .lambda. L chains and cells expressing .mu. and .gamma. H chains. Large transformed lymphocytes showing cytoplasmic Ig-staining in the pulp and interfollicular areas often have nuclear morphology indistinguishable from germinal center centroblasts. There was no evidence of primitive appearing IgM-positive cells and IgG-positive cells of more mature morphology. Immunoenzymatic staining showed that cells simultaneously expressing both IgG and IgM are only rarely encountered. When such cells were detected, the morphology was not that of a blast cell, but rather of a plasma cell containing Russell bodies. Cytoplasmic IgM switching to IgG is possibly rarely detected by immunohistological methods in reactive tissue. Double staining for .kappa. and .lambda. reavealed that cells simultaneously expressing both L chain types were not detected even among cells showing the most primitive morphology.