Immune response in the bovine mammary gland after intestinal, local, and systemic immunization

The immune response in mammary glands of cattle was measured after intestinal, local, and systemic immunization with T4 bacteriophage. Nonlactating pregnant cows were immunized by infusions into the intestine or mammary gland and by subcutaneous injections in the region of the prescapular or external inguinal lymph nodes. Titers of antibodies of different isotypes were measured in serum and in lacteal secretions by enzyme-linked immunosorbent assay, and numbers of cells producing antibodies of each isotype were determined in lacteal secretions by the Jerne plaque assay. Substantial increases in immunoglobulin G subclass 1 (IgG1) and IgG2 antibody titers were detected in serum and lacteal secretions of animals immunized through an intestinal fistula. IgM and IgA antibody responses were low or undetectable. Low numbers of IgA and IgG1 plaque-forming cells were occasionally detected. It is proposed on the basis of these data that migration of antigen-stimulated IgG lymphoblasts, and perhaps of antigen, to spleen and peripheral lymph nodes may be dominant events after intestinal immunization of ruminants. This is consistent with the predominance of serum-derived IgG antibodies in colostrum and milk. Intramammary infusion of antigen gave rise to increases in antibody titers in all classes which were greater not only in lacteal secretions but also in blood serum than with either systemic route used. There was clear evidence from relative antibody titers for local synthesis of antibodies, principally IgA and IgG1, in the immunized glands. Comparison of IgA titers in secretions from the immunized glands with those in serum also suggested that locally synthesized IgA antibodies may have contributed in some measure to serum titers. Local synthesis in both immunized and nonimmunized glands was also reflected by the presence of increased numbers of IgA and IgG1 plaque-forming cells. It is hypothesized that antibody-forming cells responsible for local synthesis originated in lymphoid tissue within the mammary gland or from peripheral lymph nodes, depending upon the route of immunization.