Changes in natural killer activities in experimental secondary amyloidosis

Natural killer (NK) cell activity in experimental murine amyloidosis was studied. In CBA/J mice, which show a high incidence of amyloidosis, NK activity was significantly decreased after 1 week of casein treatment. In C3H mice, which show a low incidence of amyloidosis, NK activity was not changed by casein treatment. Pretreatment with lipopolysaccharide in vivo enhanced the NK activities in CBA/J and C3H mice. These increases were not observed after casein treatment. The lowered NK activity of cells from CBA/J mice after casein treatment was restored to the normal range by indomethacine in vitro. Depletion of adherent cells from the spleen cells treated with casein had no effect on NK activity. Single-cell assay showed that casein treatment impaired the killing but not the binding of NK cells to target cells. After casein treatment, the splenic serum amyloid A (SAA) level gradually increased in CBA/J mice but remained low in C3H mice. NK activity was suppressed by the addition of serum obtained from CBA/J mice treated with casein but not by normal control serum. And partially purified AA protein obtained from the spleen of CBA/J mice treated with casein also suppressed NK activity in vitro.