White blood cells in infants with congenital toxoplasmosis: transient appearance of cALL antigen on reactive marrow lymphocytes.

Existing serological methods for diagnosing congenital toxoplasmosis are inadequate. We have therefore characterized the features of peripheral blood cell counts and smears in a prospective study of 8 affected infants during their first year of life. Enlarged, vacuolated lymphocytes were observed in all patients. Six patients had periods of neutropenia; in 1 patient the neutropenia was severe and prolonged. A bone marrow aspirate from this patient showed enhanced myelopoiesis, and after stimulation with hydrocortisone, but not with adrenaline, his neutrophil count normalized. Phenotyping of his bone marrow cells revealed that approximately 55% of both the immature and mature B lymphocytes were positive for the cALL antigen. Of the 8 patients, 6 had mild eosinophilia, 4 had mild monocytosis and 3 had increased numbers of plasma cells in the peripheral blood. These findings may reflect the activity of the congenital toxoplasma infection and may thus contribute to the diagnosis, particularly in patients with silent serology.