Figure 1.

A549 cells immunostained with anti-K18 pAb. The appearance of the keratin cytoskeleton is critically dependent on the fixation procedure. A characteristic “diffuse” staining pattern is seen when cells are fixed directly in formaldehyde (A, B). This appearance is due to the presence of large numbers of small, keratin-positive particles that occupy the interspaces between the filaments (C). In contrast, a well-developed KIF network is observed when cells are treated with a nonionic detergent (Triton X-100 buffer) before being fixed in formaldehyde (D). A similar filamentous pattern is seen in cells fixed directly in methanol (not shown). The presence of an extensive network of filamentous keratin after each of the last 2 protocols correlates with the absence of keratin particles. Confocal images recorded initially in color, then converted to gray scale and displayed in reverse contrast. Scale bars = 20 μm (A); 10 μm (B, D); 2 μm (C).