Echinococcus multilocularis: relationship between persistent inflammation, serum amyloid A protein response and amyloidosis in four mouse strains

LPS-hyporesponsive (C3H/HeJ) and LPS-sensitive (C57BL/6, CBA/J, C3H/HeSn) strains of mice were infected intraperitoneally with 50 alveolar hydatid cysts (AHC) to assess the effect of protracted severe inflammation on serum amyloid A protein (SAA) concentrations, splenic amyloid deposition, and pre- and postamyloidotic alterations in the splenic architecture. In general, the SAA concentrations in all the four mouse strains showed a moderate but steady increase throughout the course of infection. Splenic amyloid deposition commenced between 6 to 8 weeks postinfection (p.i.) when the SAA concentrations were relatively low and increased progressively until 12 weeks p.i. when 52 to 78% of the splenic parenchyma was obliterated. CBA mice which harbored the largest AHC throughout the 12-week course of infection showed the poorest SAA and amyloid responses; the situation was reversed in the C3H/HeSn strain. Histologically, most of the splenic follicles, during the stage of maximum amyloid deposition, appeared hypocellular. Their T-cell-dependent periarterial sinuses were either totally depleted of cells or contained plasma cells or myeloid cells. These results show that (a) there is no direct correlation between the intensity of inflammation, SAA concentrations, or amounts of amyloid deposition in either of the four mouse strains and (b) amyloidosis secondary to AHC infection differs from other experimental mouse models of amyloidosis in the magnitude of SAA elevation during the preamyloid phase.