Natural autoantibodies cytotoxic for thymus cells and for neuraminidase-treated leukemia cells in the sera of normal AKR mice

The sera of normal AKR mice were found to contain two types of naturally occurring autoantibodies. Autoantibodies cytotoxic for mouse thymus cells in the presence of guinea pig complement were of the IgM class and were heat-labile. They exerted a cytotoxic effect on syngeneic and allogeneic thymus cells but not on lymph node and spleen cells. Absorption experiments indicated that the antigen with which these autoantibodies react was present in all examined tissues of AKR mice. The concentration of the antigen was about 8 times higher on thymus cells than on other types of lymphoid cells. The cytotoxicity of normal AKR sera on thymus cells could be inhibited by various simple sugars; D-mannose, α-methyl-D-mannopyranoside, and L-fucose were the most potent inhibitors of autoantibodies to thymus cells. Autoantibodies reactive with neuraminidase-treated AKR leukemia cells were also IgM in nature, were heat-labile, and could be absorbed by various tissues of AKR mice. Neuraminidase-treated leukemia cells were more effective in absorbing these autoantibodies than were untreated leukemia cells. The cytotoxic activity of these autoantibodies could be completely inhibited by D-galactose, lactose, and L-fucose and inhibited to a lesser extent by α-methyl-D-mannopyranoside.