Immune responses in pulmonary lymph of sheep after intrabronchial administration of heterologous erythrocytes.

The response of the lower respiratory tract to intrabronchial administration of horse red blood cells (HRBC) was studied in sheep by continuous monitoring of efferent lymph issuing from the regional caudal mediastinal lymph node. The immune response was assessed by enumerating direct and indirect plaque-forming cells (PFC) in pulmonary lymph, bronchoalveolar lavage, and blood as a function of time after immunization. Within 3 days, PFC began to appear in pulmonary lymph, reaching a peak between Days 5 and 7. During the primary immune response, PFC were not detected in either bronchoalveolar lavage or blood. A second antigenic challenge resulted in a rapid, marked increase in lymph PFC, predominantly of the indirect type. Plaque-forming cells in lung lavage and blood, although observed after a secondary challenge, were inconsistent, particularly with the lower dosages of antigen. Within the narrow range of antigen dosage used, there was a clear dose-response relationship for a lymph-borne PFC during both the primary and secondary immune response. As with PFC, a high titer of antibody in lymph preceded its appearance in serum. The results indicated that monitoring efferent lung lymph can be a very sensitive and reproducible method to assess various aspects of pulmonary immune responses. In contrast, bronchoalveolar lavage elements did not effectively reflect the status of immune reactivity in the lower respiratory tract.