Plunder of Human Blood Leukocytes Containing Ingested Material, by Other Leukocytes: Where Is the Fusagen That Allows Preservation of Membrane Integrity and Motile Function?

In studying phagocytosis of zymosan particles by human blood monocytes in phase-contrast videomicroscopy, we found that monocytes loaded with zymosan particles became chemotactic for polymorphonuclear leukocytes (PMN) which closed on them and purloined their particle content. This despoliation usually occurred in monocytes that had begun to swell—prefiguring their death. The violent seizure of their contents by the aggressing PMN often tore the monocytes apart. However, some apparently healthy monocyte survived the removal of zymosan content by PMN or, more commonly, its removal by another monocyte. PMN—a much hardier cell in slide preparations—that were similarly loaded with zymosan particles, also attracted PMN. The latter could remove zymosan from the target cell without killing it. Thus, leukocytes were sacrificing significant portions of themselves without losing residual membrane integrity and motile function. Their behavior with respect to other particles (e.g., bacteria) will be of interest. We suggest that the membrane fusagen resides in the inner membrane leaflets when they are brought together in an extreme hourglass configuration. This event may be similar to the fragmentation of erythrocytes into intact pieces, the formation of cytokineplasts, the rear extrusion of content by migrating cells on surfaces, and the phagocytic process itself.