Expansion of Immature Thymic Precursor Cells in Peripheral Blood after Acute Marrow Suppression

Abstract

Leukemoid reactions occur in response to a number of infectious agents and sometimes may be associated with bone marrow suppression. After acute suppression of the bone marrow, a resurgent hyperplasia occurs that may appear as synchronous maturation of a single cell type. The authors describe the case of a 13-year-old child in whom a remarkable lymphocytosis developed during a period of pancytopenia associated with a febrile syndrome resembling Ehrlichiosis. Most of these lymphoid cells were morphologically similar to large granular lymphocytes (LGLs), but many appeared to be less mature. Immunophenotypic studies demonstrated most of these lymphoid cells to be immature T cells at an "intermediate" or "transitional" stage of thymocyte differentiation characterized by the CD1-CD3+CD4-CD8- phenotype, as well as positivity for nuclear terminal deoxynucleotidyl transferase. In T-cell ontogeny, this stage represents a transition between thymic precursors and mature thymocytes. Their presence in the peripheral blood of this child is thought to represent a lymphocytic leukemoid response to his infection. Cases such as this may be confused with malignancy.