Frequent expression of haemopoietic and non-haemopoietic antigens by reactive plasma cells: an immunohistochemical study using formalin-fixed, paraffin-embedded tissue

Unlike other B cells, plasma cells (PC) react with only a few antibodies ag ainst haemopoietic antigens. We investigated 36 specimens exhibiting a reac tive increase in PC numbers (i.e. plasmacytosis, PC hyperplasia) with a bro ad panel of antibodies suitable for use on formalin-fixed, paraffin-embedde d tissue, and compared the findings with those obtained in 51 cases of mult iple myeloma (plasmacytoma). Regardless of the immunostaining pattern for immunoglobulin light and heavy chains, reactive PC reacted with at least two and at most six of seventeen antibodies detecting haemopoietic antigens [Ber-H2/CD30 (91%), anti-leucoc yte common antigen (LCA)/CD45 (86%), KP1/CD68 (64%), MB2 (57%), 4KB5/CD45RA (37%), DF-T1/CD43 (28%), UCHL1/CD45RO (20%), L26/CD20 (17%), MT2 (14%) and Mac387 (8%)], and with at least one and at most four of six antibodies aga inst non-haemopoietic antigens [antiepithelial membrane antigen (EMA) (94%) , antivimentin (77%), anti-pan-cytokeratin/KL1 (74%), BMA120 (51%) and HMB4 5 (14%)]. Five antibodies stained reactive PC significantly more often than neoplasti c PC: Ber-H2/CD30 (p less than or equal to 0.0000), KP1/CD68 (p less than o r equal to 0.0000), anti-LCA/CD45 (p less than or equal to 0.0000), anti-EM A (p less than or equal to 0.0339) and anti-pan-cytokeratin/KL1 (p less tha n or equal to 0.0000). The more frequent and more heterogeneous expression of antigens by reactive PC suggests that the aberrant immunoreactivity of n eoplastic PC in plasmacytoma is not due to the process of malignant transfo rmation in an early step of B-cell differentiation, but could reflect the h eterogeneity of antigen expression by normal PC.