Local immune responses in the bovine fetus vaccinated in utero with Escherichia coli antigen.

Using specific immunofluorescent examinations, the local immune responses were studied in 14 calves prenatally vaccinated (10 to 50 days before birth) with Escherichia coli (O26:K60:NM) antigen or sterile saline solution. All calves were colostrum-deprived, were given oral doses of homologous organisms (killed or live), and were necropsied either at birth or within 12 days after birth. Immunofluorescent plasma cells were not seen in duodenum, jejunum, jejunal lymph nodes, ileum, ileal lymph node, or spleen of control calves prenatally vaccinated with sterile saline solution. All of these tissues, except ileal lymph node, from calves vaccinated in utero with E coli showed fluorescence. Jejunum, jejunal lymph node, and ileum had the greatest number of immunofluorescent plasma cells. There were more immunoglobulin G2-than immunoglobulin M-producing cells. The cells producing specific antibodies against E coli (1 calf studied) comprised approximately 33% of the total number of immunofluorescent cells.