Ultrastructural studies of complement mediated cell death: a biological reaction model to plasma membrane injury.

Complement-mediated nucleated cell death has been shown to be independent of colloid-osmotic swelling. In contrast, other factors (e.g. Ca2+ influx) are of importance in the induction of cell death. In this communication, the sequential morphological features of complement-mediated cell injury have been studied by electron microscopy and compared with biochemical data (ATP content and LDH release). It was observed that immediately after C5b-8 lesion formation, although the overall cell, morphology is well preserved, the mitochondria display an "ultracondensed" appearance. Upon addition of C9, the mitochondria remain initially condensed, but swell progressively with final formation of flocculent densities. The nuclei become progressively edematous, with concurrent disappearance of heterochromatin. The nucleoli lose their associated chromatin and display segregation of their components with formation of markedly electron-dense filamentous deposits. The nuclear envelope remains initially intact, but subsequently progressive dilatation of the associated perinuclear RER cisterna and distention of the nuclear pores associated with leakage of chromatin into the cytoplasm are seen. The larger cell organelles (including mitochondria, ER, Golgi apparatus, etc.) become clustered around the nucleus, concurrently with marked edema of the outer cytoplasm and bleb formation. The RER cisternae become dilated, whereas the Golgi complex disappears. Relatively early on the plasma membrane shows breaks in continuity. The pattern of these changes--potentially related to Ca2+ influx, ATP efflux and overall metabolic depletion--corresponds to the previously described model of cell reaction to injury, confirming the dynamic nature of the process. The morphology of cell death in this model shares some features, e.g., the nucleolar changes, with "apoptosis" (programmed cell death). However, the overall pattern appears to correspond more to "necrosis," characterized by loss of volume control and mitochondrial abnormalities.