The lymph-borne response of foetal lamb lymph nodes to challenge with Brucella abortus in utero

The cannulated prescapular lymph node of the foetal lamb was challenged with killed Brucella abortus. Usually, both efferent prescapular ducts were cannulated and one node left as a control. Nodes were given primary or secondary challenges with doses of 10(9) - 2 X 10(10) brucella organisms and the lymph-borne response of the nodes followed. The foetal lymph node produced a vigorous cellular response to the injected brucella, restricted to the challenged side. The total cell output and, more strikingly, large cell output increased to reach a peak value 4-5 days after challenge. This cellular response was seemingly dose-dependent. The output of antibody after a primary challenge was delayed considerably and could not be detected in the lymph until well after the cellular response had subsided. The concentrations of antibody produced were quite low and almost all mercaptoethanol-sensitive. With secondary challenges the output of antibody occurred much more quickly, in phase with the cellular response, and appreciable amounts of mercaptoethanol-resistant antibody were produced. Under exceptional circumstances, high titre, highly specific anti-brucella antibody has been produced in foetal lymph. The foetal lymph node provides a powerful tool for further studies of the ontogeny of the immune response, and might help elucidate the failure of newborn animals to respond to some important bacterial antigens.