Ability of Monoclonal Anti-D Antibodies to Promote the Binding of Red Cells to Lymphocytes, Granulocytes and Monocytes

Abstract

Red cells sensitized with IgGl or IgG3 monoclonal anti-D antibodies were used in rosette assays with human lymphocytes, monocytes and granulocytes. With all three cell types, IgG3 antibodies promoted a greater degree of rosette formation than IgGl antibodies. Monocytes required a minimum of about 0.5 x 10^3 IgG3 molecules per red cell for rosette formation, and granulocytes and lymphocytes required around 1 x 10^4 IgG3 molecules per red cell. Approximately 80% of monocytes and granulocytes and 10% of lymphocytes were capable of rosette formation. These results are consistent with differences in the number and affinity of Fc receptors on different leucocytes. When compared with previous data these results suggest that binding of monocytes to monoclonal anti-D sensitized red cells is very similar to that of red cells sensitized with polyclonal antisera. Lymphocytes and granulocytes, however, appear to bind less well to red cells sensitized with certain monoclonal antibodies than with polyclonal antibodies. These findings may be of relevance to the prophylactic use of monoclonal anti-D antibodies.

Neutrophil‐erythrocyte rosettes in autoimmune hemolytic anemia

“…This may be explained by in vitro studies demonstrating markedly different thresholds for rosette formation by monocytes and neutrophils, at approximately 200 and 5000 molecules of IgG per RBC, respectively [1] (for comparison, most DAT assays are standardized to become positive when there are 500 IgG molecules per RBC). These studies demonstrate that while monocyte-erythrocyte rosette formation is less efficient with IgG1 than IgG3, neutrophil-erythrocyte rosette formation with IgG1 is negligible even at very high titers [3]. We predict but are unable to prove that our patient's AIHA was due to one or more IgG3 antibodies, consistent with the high affinity but low titer antibody detected.…”

“…Many details of rosette formation in vivo are unknown because the phenomenon is encountered so infrequently, but in vitro studies suggest that rosettes are more likely to form with cells of the monocyte lineage than with other leukocytes [1][2][3]. Here, we present a rare case of severe autoimmune hemolytic anemia with neutrophil-erythrocyte rosettes on peripheral blood smear (Image 1).…”