Both Murine SAA1 and SAA2 Yield AA Amyloid in Alveolar Hydatid Cyst-Infected Mice

Amyloid susceptible C57BL/6 and partially amyloid resistant A/J mice, infected intraperitoneally with 250 alveolar hydatid cyst (AHC), the larval stage of a cestode parasite Echinococcus multilocularis , develop multiple organ amyloid deposits at approximately 1 and 4 weeks post infection (p.i.), respectively. Pooled spleens and livers from each mouse strain, at 8 and 10 weeks p.i., were used for the purification of protein AA utilizing a HiLoad Superdex 200 column equilibrated with 5 M guanidine-HCl. Protein AA from each mouse strain was separated on 16% Tris-tricine SDS-PAGE gels and immunoblotted with monospecific rabbit anti-mouse AA IgG; five and six immunoreactive AA subspecies were detected in the C57BL/6 and A/J materials, respectively. N-Terminal amino acid sequence analysis was performed on the bulk column-purified protein AA as well as on the electroblotted AA subspecies from each mouse strain. The results show a mixture of serum amyloid A₁ (SAA₁) and (SAA₂)-derived AA protein from each mouse strain; SAA₁-derived AA, although alluded to, has never been demonstrated as tissue deposits in mice. These findings suggest that the intense and persistent inflammatory processes in AHC-infected mice may have induced conversion of weakly amyloidogenic SAA₁ to AA. This conversion could be detected by amino acid sequencing of electrophoretically separated AA subspecies.