Quantitative evaluation of antibody‐dependent lymphocyte‐mediated lysis of human red cells

The ability of lymphocytes to lyse human red cells coated with anti‐D antibody was assessed by measuring 51 Cr release from labeled red cells incubated with peripheral blood leukocyte suspensions from 12 normal donors. Mixed mononuclear cell suspensions (containing monocytes and lymphocytes) from all donors produced lysis of sensitized red cells. Treatment with carbonyl iron reduced monocyte concentration to less than 1.2% in all donors, as measured by morphologic criteria, esterase staining and ingestion of latex particles. Lysis of red cells following monocyte depletion was markedly reduced in 8 of the 12 donors. Despite depletion of monocytes, unchanged or increased lysis was noticed with the leukocytes of the remaining 4 donors. This lysis was due to lymphocytes, not to residual monocytes. If target red cells were treated with papain or trypsin prior to sensitization, marked lysis occurred with lymphocytes of all donors, including those which did not lyse unmodified red cells. Direct cytolysis of sensitized red cells during contact with small lymphocytes was recorded using microcinematography, which confirmed the role of lymphocytes in mediating lysis. Lymphocyte‐mediated lysis of red cells increased with mounting levels of antibody sensitization regardless of prior treatment with papain. Papain increased antibody coating per red cell, yet lysis per molecule of antibody bound was also increased. Lysis was inhibited by IgG1 and IgG3 in the fluid phase but not by IgG2 or IgG4. At an equivalent level of antibody sensitization lysis was augmented by concurrent coating of the red cells with C3b, C3d and/or C4b, though these components could not produce lysis in the absence of antibody coating.