An antigen characteristic of hairy cell leukemia cells is expressed on certain activated B cells

A murine monoclonal antibody, anti-HC2, which reacts with hairy cell leukemia cells, was used to define the normal cell equivalent for the leukemic hairy cell. This antibody stained the membranes of 2.24% of normal peripheral blood lymphocytes. These cells were more common in T cell-depleted cell populations, and bore membrane immunoglobulin. Some B lymphoblastoid cell lines were also anti-HC2-positive. Examination of normal B cell subpopulations revealed that HC2-positive cells frequently co-express an activation antigen and membrane IgG. Cell populations enriched for HC2-positive cells contained the bulk of PWM-responsive B cells. These data suggest that HC2-bearing B cells are activated B cells. B cell differentiation induced in vitro by PWM with T cell helper factors resulted in an increase in the number of HC2-positive cells at day 4 or 5 of culture. The HC2-positive cells were no longer present at the time of maximal plasma cell differentiation on day 7 of culture. By using B cells from a patient with the hyper-IgM syndrome that are incapable of immunoglobulin heavy chain class switching, it was demonstrated that HC2 expression did not require prior heavy chain switch. The m.w. of the HC2 antigen was 52 to 63 KD. Four bands with different isoelectric points were discerned on two-dimensional analysis. We suggest that hairy cell leukemia represents a malignancy of activated B cells. A unique stage of B cell differentiation is identified by the HC2 activation antigen.

Modulation of mononuclear phagocyte function by intravenous gamma-globulin

To assess the effects on mononuclear phagocyte function of i.v. gamma-globulin treatment in idiopathic thrombocytopenic purpura, we examined in vivo and in vitro mononuclear phagocyte function in 11 patients before and after therapy. All patients, both splenectomized and non-splenectomized, demonstrated a prolongation of in vivo clearance of autologous IgG-sensitized erythrocytes (p less than 0.01). Concurrent in vitro assessment of blood monocyte function showed decreased IgG-sensitized erythrocyte (EA) rosette formation (mean +/- SD: 31.6% +/- 8.2 vs 24.5% +/- 9.5; p less than 0.03) and decreased affinity of Fc receptor-specific IgG oligomer binding (9.9 +/- 16.3 vs 1.8 +/- 2.1 X 10(8) M-1; p less than 0.008), but no consistent change in the estimate of the maximum number of binding sites. Phagocytosis of two different EA probes was decreased (EhuA:0.49 +/- 0.26 vs 0.25 +/- 0.14 erythrocyte/monocyte/hr; p less than 0.02, EoxA: 1.76 +/- 0.66 vs 1.27 +/- 0.67 erythrocyte/monocyte/hr, p less than 0.05). The change in in vivo mononuclear phagocyte system clearance was significantly correlated with the change in the association constant for oligomer binding (r = 0.98, p less than 0.05). These data demonstrate that i.v. gamma-globulin infusions induce alterations of mononuclear phagocyte function that are not dependent on the presence of autologous serum containing infusate. The change in apparent Fc receptor affinity rather than receptor number may reflect an altered Fc receptor population with different binding properties.

Modulation of mononuclear phagocyte function by intravenous gamma-globulin

To assess the effects on mononuclear phagocyte function of i.v. gamma-globulin treatment in idiopathic thrombocytopenic purpura, we examined in vivo and in vitro mononuclear phagocyte function in 11 patients before and after therapy. All patients, both splenectomized and non-splenectomized, demonstrated a prolongation of in vivo clearance of autologous IgG-sensitized erythrocytes (p less than 0.01). Concurrent in vitro assessment of blood monocyte function showed decreased IgG-sensitized erythrocyte (EA) rosette formation (mean +/- SD: 31.6% +/- 8.2 vs 24.5% +/- 9.5; p less than 0.03) and decreased affinity of Fc receptor-specific IgG oligomer binding (9.9 +/- 16.3 vs 1.8 +/- 2.1 X 10(8) M-1; p less than 0.008), but no consistent change in the estimate of the maximum number of binding sites. Phagocytosis of two different EA probes was decreased (EhuA:0.49 +/- 0.26 vs 0.25 +/- 0.14 erythrocyte/monocyte/hr; p less than 0.02, EoxA: 1.76 +/- 0.66 vs 1.27 +/- 0.67 erythrocyte/monocyte/hr, p less than 0.05). The change in in vivo mononuclear phagocyte system clearance was significantly correlated with the change in the association constant for oligomer binding (r = 0.98, p less than 0.05). These data demonstrate that i.v. gamma-globulin infusions induce alterations of mononuclear phagocyte function that are not dependent on the presence of autologous serum containing infusate. The change in apparent Fc receptor affinity rather than receptor number may reflect an altered Fc receptor population with different binding properties.

Human dendritic cells: major stimulators of the autologous and allogeneic mixed leucocyte reactions

Highly purified preparations of dendritic cells were obtained from human peripheral blood. Loosely adherent cells were selected and subsequently depleted of phagocytic cells and Fc receptor positive cells to yield the dendritic cell fraction. These isolates contained greater than 90% Ia positive cells, with many of the cells showing the morphological characteristics of the murine dendritic cell. These preparations were compared to other mononuclear cell fractions as stimulating cells in autologous and allogeneic mixed leucocyte reactions. The dendritic cell preparations provided the most potent stimulus for autologous T cell proliferation, with 10 x more 3H-thymidine incorporated by T lymphocytes incubated with autologous dendritic cells than with any other non-T cell preparation. Dendritic cells were also the most stimulatory cell in the allogeneic mixed leucocyte reaction, although the non-adherent subpopulation produced some stimulation of allogeneic T cells. In separate experiments, it was determined that B cells could be activated by pokeweed mitogen to vigorously stimulate autologous T cells. Visual observation of cluster formation in cultures containing dendritic cells and autologous T cells suggests that the capacity for intimate cell contact may be an important property of the dendritic cell in vivo.