Minnesota miniature piglets obtained by hysterectomy and deprived of colostrum were examined for the presence of immunoglobulin by immunoelectrophoresis, double-gel diffusion, and radial immunodiffusion techniques with specific anti-immunoglobulin chain sera. A large amount of variability existed between different litters of piglets and between different piglets within the same litter, ranging from no detectable immunoglobulin in the serum to very high immunoglobulin levels approaching that of the adult pig. All known classes of porcine immunoglobulin including immunoglobulin G, immunoglobulin M, and immunoglobulin A could be found in the sera from litters where there was extensive placental damage. This contaminating immunoglobulin was shown to have antibody activity to actinophage MSP-2 even when present in very low concentrations. The low level contamination with immunoglobulin G, which was the most frequently encountered type of contaminant, was demonstrated to be similar to sow immunoglobulin G both antigenically and in its molecular size. The data demonstrates that individual piglets must be tested for immunoglobulin content rather than being assumed to be immunologically "virgin" and emphasizes the need for an intact placenta barrier to obtain piglets free from maternal immunoglobulin and devoid of antigenic stimulation.

Summary Biphasic responses and differing rates of neutralizing activity of early and late sera from BALB/Sy mice given single and multiple injections of actinophage indicated two types of antibodies in phage neutralization. By the use of physical and immunochemical techniques the neutralizing activity of early serum was found to be associated with a γ1-immunoglobulin of the 19 S class. The late serum contained mostly a γ2-immunoglobulin of the 7 S class. The early 19 S antibody was inactivated by 2-mercaptoethanol in contrast to the stability of the late 7 S γ2 antibodies. Immunoelectrophoretic patterns of pooled mouse sera were typical of rabbit and human patterns. In the mouse, however, mercaptoethanol dissociates the so-called β2M into a new component with the mobility of, but antigenically distinct from, the γ2-immunoglobulin. In the mouse, the 19 S immunoglobulin is not related to the classical β2M line but is associated with the fast γ2-globulin and appears antigenically identical. The implication of the apparent close relationship of these two classes of immunoglobulin is discussed in relation to the mechanism of their production.