Fig. 5.

Lymph node showing lymphocyte depletion and prominent polyclonal plasmacytosis with increased proliferation in acute infection: (A, B) show an architecturally intact lymph node with patent subcapsular and medullary sinuses, many with reactive histiocytosis. There are almost no apparent follicles and lymphocytes are diminished, with the parenchyma (C, D) mostly replaced by a population of small to medium-sized plasma cells and plasmacytoid forms with occasional markedly enlarged, hyperchromatic nuclei or binucleated forms, as well as ones with more dispersed chromatin and prominent nucleoli. (E) CD3+ T cells and CD20+ B cells are markedly reduced, with only rare CD21+ follicular dendritic cell meshworks. The plasma cell population shows dim-to-negative CD138, uniform MUM1 expression, and considerably increased Ki-67 proliferation (approximately 50%) but polytypic kappa and lambda light chain expression.