Solubilization studies and properties of particulate NAD-independent malate dehydrogenase of Acinetobacter calcoaceticus (N.C.I.B. 8250).

Erythrocytes from the same mouse strains gave similar results; here the cell number was increased to 109/ml to obtain a significant difference between curves for highand low-responder mice. It is possible that these results are affected by contamination with mouse ferritin from the spleen or plasma despite washing of cells. To minimize possible contamination by mouse ferritin, lymph-node cells, similarly washed, were used, and again low-responder A.Thy 1.1 cells showed significantly more cross-reactivity than did high-responder BlOD2 ceIls (Table 1). The addition of cells from highand low-responder strains of mice to the radioimmunoassay system changed the characteristics of the antiserum-dilution curve. Low-responder cells consistently produced a greater shift of the curve to the left than did highresponder cells, demonstrating that there is some cross-reactivity between antigens on the cell surfaces and ferritin. The difference between the curves for highand low-responder cells indicates that lowresponder cells cross-react to a greater degree with ferritin than do high-responder cells, and this difference is observed with spleen cells, lymph-node cells and erythrocytes. The large number of erythrocytes used to obtain a significant difference between highand low-responder strains possibly indicates that the cross-reactant on the erythrocyte surface is present at a lower concentration than on the other cells tested. The results of this study indicate that the responder status of different strains of mice after immunization is reflected in the degree of cross-reactivity between self-determinants and the test antigen such that low responders cross-react with antigen to a greater extent than do high-responder animals. The concept of immune-response gene thus appears to be unnecessary to explain high and low immune responses to ferritin in different strains of mice, because it may depend on the extent of cross-reactivity between self determinants and antigen.