AA amyloid protein in the fecal amyloid fibril fraction is required for transmission. (a) The fecal amyloid fibril fraction from C90 was untreated (UT), immunodepleted with normal rabbit IgG (ID-IgG) or anti-cheetah AA antiserum (ID-AA) for one cycle (Left) or five cycles (Right) and then were separated with 16.5% SDS/PAGE followed by immunoblotting with anti-cheetah AA antiserum (10 μl per well). (b) UT and ID-IgG or ID-AA for five cycles of immunodepletion were used to induce AA amyloidosis in C57BL/6 mice (four mice per group). The amount of amyloid deposited was graded in Congo red-stained sections. (c) AA amyloid protein levels in the spleens from mice exposed to UT, ID-IgG, or ID-AA for five cycles of immunodepletion. AA amyloid proteins were isolated from each group mice, and Western blots were analyzed (20 μg of protein per well) followed by quantitative analysis using National Institutes of Health Image. The means and SE were determined by the relative ratios of AA amyloid protein levels for each induced group versus the group induced by the untreated sample (*, P < 0.05; **, P < 0.01).