Some quantitative aspects of the human monocyte erythrophagocytosis and rosette assays.

The sensitivity of peripheral blood mononuclear phagocytes (PBMPs) in the red cell (RBC) adherence and erythrophagocytosis assays were investigated using anti-D of subclasses IgG1 and IgG3. Particular emphasis was placed on identifying variability between PBMP preparations from different healthy donors. About 500 molecules of IgG1 type anti-D per RBC and about 100 molecules of IgG3 antibody per RBC were the lowest levels of sensitization which elicited a weak, positive test. Considerable variation between different preparations was seen, and it appeared that the capability of a PBMP preparation to react with weakly sensitized RBCs may not be closely related to its strength of reaction with strongly sensitized cells. PBMPs which were recovered after storage in liquid nitrogen were more reactive in both assays than freshly prepared PBMPs from the same donor. This study demonstrated the importance of weakly sensitized RBCs as part of the control system and indicated a need for caution when establishing a negative test result when the clinical significance of RBC antibody is being investigated.