AN EXPLANATION FOR THE HETEROGENEITY IN B LYMPHOCYTE ECTO-5′-NUCLEOTIDASE (ECT0–5′-NT) ACTIVITY IN PATIENTS WITH HYPOGAMMAGLOBULINEMIA: 208

Abstract

Ecto-5'-NT activity was measured in human B cells at different stages of development and compared with the B cells' capacity to synthesis Ig in vitro. Ecto-5'-NT activity was higher in adult B cells from peripheral blood, spleen, or lymph node than in B cells from fetal spleen or cord blood (27.9±12, 29.2 and 33.8 vs 5.02 and 5.59±2.8 nmol/hr/10⁶ cells, respectively). B cell ecto-5'-NT activity increases shortly after birth and is reflected by gradual increases in total lymphocyte ecto-5'-NT activity from 7.0±2.1 in cord blood, to 14.0±4.2 nmol/hr/10⁶ cells in normal infants at 6 mo. B cells from cord blood or 6 mo. old infants could synthesize IgM, but not IgG, in response to Epstein Barr virus (EBV). Adult peripheral B cells separated into mature pokeweed mitogen (PWM)-responsive and less mature PWM-nonresponsive fractions by mouse RBC rosetting had equivalent total ecto-5'-NT activity. Thus, in normal human B cell development, the ability to synthesize IgG in vitro in response to EBV or PWM is acquired subsequent to the acquisition of ecto-5'-NT activity. Therefore, patients with hypogammaglobulinemia might have either normal or low B cell ecto-5'-NT activity depending upon the location of their block in B cell differentiation. Of 11 patients studied, 4 had normal B cell ecto-5'-NT activity while 7 had reduced activity (15.4-58.2 and 2.8-13.2 nmol/hr/10⁶ cells, respectively).

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