The study investigates the characteristics of γ1A-globulin in human parotid saliva, colostrum, and other external secretions. γ1A-globulin is predominantly found in these fluids, with a γ2/γ1A ratio much lower than in normal human serum. The research aims to elucidate the mechanisms involved in the secretion of γ1A-globulin and its properties compared to serum γ1A. Key findings include: 1. **Isolation and Properties of γ1A-Globulin**: γ1A-globulin was isolated from saliva and colostrum, and its properties were compared with those of serum γ1A. Salivary and colostral γ1A are similar to each other but differ from serum γ1A in certain chemical and immunological properties. 2. **Local Synthesis in Parotid Gland**: Fluorescent antibody and autoradiographic techniques were used to demonstrate local synthesis of γ1A in the parotid gland. This suggests that the gland may produce a unique type of antibody. 3. **Immunological Properties**: Salivary and colostral γ1A show immunological specificity, indicating the presence of antigenic determinants not found in serum γ1A. These antibodies are associated with higher polymers of γ1A present in saliva and colostrum. 4. **Fluorescent Antibody Studies**: Fluorescent antibody studies in parotid tissue sections revealed specific staining in interstitial cells and epithelial cells, suggesting that salivary γ1A is produced locally. 5. **Radioactive Labeling Studies**: Iodine-125-labeled γ1A was injected intravenously, and its distribution in saliva, serum, urine, and stool was monitored. The results indicated that the radioactivity in saliva was not bound to protein, suggesting that intact γ1A is not transported from serum to saliva. 6. **Discussion**: The study discusses possible mechanisms for the selective occurrence of γ1A in body fluids, including simple filtration, transudation, active transport, and local synthesis. The findings suggest the existence of an immune system characteristic of certain external secretions, distinct from the systemic system responsible for circulating antibodies. The study concludes that γ1A in saliva and colostrum exists largely as higher polymers, with the major component having a sedimentation coefficient of 11S. Local synthesis of γ1A in the salivary gland has been demonstrated, and the presence of immunological specificity in these fluids indicates a unique immune system.The study investigates the characteristics of γ1A-globulin in human parotid saliva, colostrum, and other external secretions. γ1A-globulin is predominantly found in these fluids, with a γ2/γ1A ratio much lower than in normal human serum. The research aims to elucidate the mechanisms involved in the secretion of γ1A-globulin and its properties compared to serum γ1A. Key findings include: 1. **Isolation and Properties of γ1A-Globulin**: γ1A-globulin was isolated from saliva and colostrum, and its properties were compared with those of serum γ1A. Salivary and colostral γ1A are similar to each other but differ from serum γ1A in certain chemical and immunological properties. 2. **Local Synthesis in Parotid Gland**: Fluorescent antibody and autoradiographic techniques were used to demonstrate local synthesis of γ1A in the parotid gland. This suggests that the gland may produce a unique type of antibody. 3. **Immunological Properties**: Salivary and colostral γ1A show immunological specificity, indicating the presence of antigenic determinants not found in serum γ1A. These antibodies are associated with higher polymers of γ1A present in saliva and colostrum. 4. **Fluorescent Antibody Studies**: Fluorescent antibody studies in parotid tissue sections revealed specific staining in interstitial cells and epithelial cells, suggesting that salivary γ1A is produced locally. 5. **Radioactive Labeling Studies**: Iodine-125-labeled γ1A was injected intravenously, and its distribution in saliva, serum, urine, and stool was monitored. The results indicated that the radioactivity in saliva was not bound to protein, suggesting that intact γ1A is not transported from serum to saliva. 6. **Discussion**: The study discusses possible mechanisms for the selective occurrence of γ1A in body fluids, including simple filtration, transudation, active transport, and local synthesis. The findings suggest the existence of an immune system characteristic of certain external secretions, distinct from the systemic system responsible for circulating antibodies. The study concludes that γ1A in saliva and colostrum exists largely as higher polymers, with the major component having a sedimentation coefficient of 11S. Local synthesis of γ1A in the salivary gland has been demonstrated, and the presence of immunological specificity in these fluids indicates a unique immune system.