Orally induced tolerance to casein in mice on normal mouse chow.

We examined the ability of bovine casein to induce oral tolerance in BDF1 mice raised on a normal mouse chow diet. Giving 20 mg casein 1 X or 4 X by intragastric tube or for 28 days at 1 mg/ml in drinking water failed to have a significant effect (P greater than 0.2) on the subsequent immune response to parenteral casein, suggesting that casein was not an effective oral tolerogen. However, we discovered that most normal mouse chow contains casein. When BDF1 mice were raised on a casein-free diet, and treated as above, they showed marked suppression of subsequent responses to parenteral casein (P less than 0.01). Our results indicated that mice on the normal diet were presuppressed by the dietary exposure. Examination of several other normal mouse chows revealed that they all contained casein as a protein source. A possible effect of prior exposure must be considered in all experimental animal studies involving immune responses to antigens which may be present in the environment.

Immune complexes and antibodies to BCG in sera from patients with mycobacterial infections.

We have examined the prevalence of circulating immune complexes in sera from patients with mycobacterial infections. Sera from 68 percent of patients with active M. tuberculosis and 58 percent of patients with M. intracellulare infections had significantly elevated Clq binding activity (Clq-BA). In general there was a fall in Clq-BA with treatment. Only 15 percent of M. tuberculosis patient with a bacteriological cure, 22 percent of non-tubercular patients with chronic obstructive pulmonary disease, and 3 percent of normal individuals had an elevated Clq-BA. Antibodies to a BCG-derived antigen were demonstrated in most of the individuals studied in all groups but, significantly elevated levels were seen only in patients with mycobacterial infections. In certain patients there appeared to be an inverse relationship between Clq-BA and BCG binding, suggesting that perhaps BCG-related antigens participated in the immune complexes found. Other possible antigen-antibody complexes are discussed.

The effect of high antigen density on solid-phase radioimmunoassays for antibody regardless of immunoglobulin class.

Human sera containing antibody to casein or to bovine serum albumin were used to assess the validity and utility of a solid-phase assay for quantitating antibody activity. Rabbit anti-human immunoglobulin radiolabeled with 125I and capable of reacting with all human immunoglobulin classes was used to detect antibody bound to antigen immobilized to polystyrene tubes by a new covalent technique. This method results in very high antigen concentrations in highly stable association with polystyrene tubes. Kinetic and absorption studies demonstrated that low avidity antibodies are better detected when antigen is immobilized by the covalent method than when passively adsorbed. Conditions are described for minimizing artifactual interactions and for obtaining results similar to those obtained with conventional, liquid-phase assays. Failure to reach equilibrium in solid-phase assays and other problems are proposed to explain, in part, the inability to obtain a better correlation between solid- and liquid-phase immunoassays.