Reorganization of microfilaments in macrophages after LPS stimulation.

Lipopolysaccharide (LPS), a potent activating substance of macrophages, induced the reorganization of microfilaments in macrophages obtained from C3H/HeN mice. At 1 min after LPS addition, a slight disassembly of actin was observed. At 2 to 4 min, there was a gradual assembly; then, at 5 and 6 min, a subsequent rapid disassembly occurred. We employed two methods to observe this process. One was the RITC-phalloidin staining of actin filaments and the other was the extraction of monomeric actin and unstable actin filaments with Triton X-100 solution. The results obtained by the two methods were basically in agreement. Nevertheless, there was a discrepancy between the results from the two methods, concerning the ratio of assembly and disassembly. The RITC-phalloidin staining was more sensitive in detecting actin assembly and less sensitive in detecting the disassembly than the extraction with Triton X-100 solution was. This difference suggests that some of the unstable filaments, which were extracted with Triton X-100 solution and fixed with formalin, were formed during the LPS-induced reorganization process. This reversible actin assembly could not be observed in the LPS-nonresponder, C3H/HeJ mouse macrophages. We concluded that the observed process could be attributed to LPS-signal triggering pathways subsequent to LPS binding and that a necessary component to initiate effective LPS-signaling, which is probably deficient in C3H/HeJ mice, is involved in this reorganization process of LPS-stimulated macrophages.