The basement-membrane-like matrix of the mouse EHS tumor: III. Immunodetection of the amyloid P component in basotubules

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Abstract
Immunohistochemical methods were applied to the ultrastructural localization of the amyloid P component in the EHS tumor matrix. First, the preembedding approach was used by exposing frozen sections of tumor to antiserum against the mouse amyloid P component followed by the peroxidaseantiperoxidase sequence. Second, using the postembedding approach, Lowicryl K4M sections of the tumor were exposed to antiserum against the amyloid P component and subjected to the protein A‐gold procedure. In both cases, the immunostaining was restricted to structures which appeared in longitudinal section as fairly straight rods and in cross section as 7‐ to 10‐nm pentagonal or roughly circular profiles outlining a lumen with a central dot. Since these features are characteristic of basotubules, it is concluded that the basotubules of the tumor matrix possess the antigenicity of the amyloid P component and presumably contain this substance itself. Similar experiments carried out on the thick basement membrane known as Reichert's membrane demonstrated that its basotubules also possessed amyloid P‐component antigenicity. It is likely, therefore, that the amyloid P component is a constituent of basotubules.