Lymphoid Tissues from Patients with Infectious Mononucleosis Lack Monoclonal B and T Cells

Julie A. Plumbley^*, Hongxin Fan^*, Phyllis A. Eagan^*, Aamir Ehsan^*, Bertram Schnitzer and Margaret L. Gulley^*

From the University of Texas Health Science Center at San Antonio, * San Antonio, Texas; the 81 Medical Defense Group, Keesler Hospital, Keesler Air Force Base, Mississippi; The Audie L. Murphy Memorial Veterans Hospital, San Antonio, Texas; and the University of Michigan Medical Center, Ann Arbor, Michigan

In typical cases of infectious mononucleosis (IM), lymphoid tissueis rarely submitted for pathological examination. When lymphoid tissuesfrom IM cases are examined, the histological appearance of IMmay be difficult to distinguish from malignant lymphoma. The purposeof this study was to address the utility of clinical molecular assaysfor T and B cell clonality in distinguishing IM from lymphoid malignancy.DNA was recovered from paraffin-embedded archival lymphoid tissuesof 18 cases of IM and 13 control cases representing other reactivelymphoid hyperplasias. T cell receptor ${gamma}$ (TCR- ${gamma}$ ) and immunoglobulinheavy chain (IgH) gene rearrangements were assayed using ourstandard clinical polymerase chain reaction procedures targeting eachof the four functional variable (V) families and the three joining (J)families of the TCR- ${gamma}$ gene, and framework III of the IgH gene,respectively. In 17 of 18 cases of IM, no monoclonal T or Bcell populations were detectable. One case, the only spleenspecimen in the study, had an oligoclonal pattern of TCR- ${gamma}$ rearrangements.The control cases representing other reactive hyperplasias alsolacked monoclonality. The assays used were sensitive to clonalpopulations as small as 5% of cells. In this case series, nomonoclonal lymphoid populations were identified in any caseof IM. This finding suggests that molecular studies are useful indistinguishing IM from lymphoid neoplasms.