Functional Heterogeneity of Human Cord Blood Monocytes

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Abstract
Human cord blood monocytes were separated into four different subpopulations by means of a discontinuous bovine serum albumin (BSA) gradient. Of the least dense, 31% were present in fraction A, 17% in fraction B and 13% in fraction C and of the most dense, 20% were in fraction D. The rest (17%) sedimented as a pellet, of which 93% were dead cells. The monocytes of fraction C (density ≤ 1.070) demonstrated suppressor activity on in vitro antibody synthesis of maternal B cells. Fraction D (density ≤ 1.075) monocytes enhanced antibody synthesis of maternal B cells compared with synthesis produced in a similar experiment with unfractionated monocytes. Addition of either fraction A or B monocytes to the mixed culture of T and B cells resulted in antibody production comparable to that produced by addition of unfractionated monocytes. The functional heterogeneity of the cord monocytes was assayed also by 2-deoxyglucose (2-DOG) uptake, a marker for immunological macrophage activation. Fractions A and D showed significantly higher 2-DOG transport than that of unfractionated monocytes; in contrast, fraction C showed a 50% reduction of 2-DOG uptake. Furthermore, in contrast to fraction D, fraction C possessed only minimal phagocytic activity (for antibody-coated sheep erythrocytes) and minimal hemoxygenase enzyme activity. These data demonstrate functional heterogeneity of cord blood monocytes.