Human monocyte functional heterogeneity: monocyte fractionation by discontinuous albumin gradient centrifugation

Human monocytes subserve many roles in the immune response. It is not clear, however, whether this functional heterogeneity reflects the action of different monocyte subpopulations. We separated human blood monocytes into distinct populations using a discontinuous (15-35%) serum albumin gradient technique. We examined if any of a number of monocyte functions were preferentially expressed by these five monocyte subsets. Monocytes in the 25% and 30% albumin fractions possessed more Fc (IgG) and C3 receptor activity than did monocytes in either of the 15, 20 or 35% fractions. In addition, monocytes isolated in the more dense albumin fractions were enriched for the capacity to support pokeweed mitogen-induced B-cell differentiation. All gradient fractions were equally capable of binding Raji cells and inhibiting Raji cell incorporation of [3H]thymidine. These data indicate that fractionation of monocytes by a discontinuous albumin gradient is an effective method to enrich for those monocytes with certain functional characteristics.