Effects Of NO2 on immune responses in pulmonary lymph of sheep

Sheep in which the efferent duct of the caudal mediastinal lymph node was cannulated were exposed to 5 ppm No2, 1.5 h/d for 10 or 11 d. Immune responses were assessed by measuring the daily output of hemolytic plaque-forming cells (PFC) in pulmonary lymph, following intrabronchial immunization with horse red blood cells (HRBC) and phytohemagglutinin- (PHA) induced transformation of blood and pulmonary lymph lymphocytes. Sheep immunized 2 d after termination of NO2 exposure had reduced outputs of PFC as compared to those seen in sheep challenged 4 d after NO2 exposure. Animals immunized 4 d after NO2 exposure had outputs similar to those of air control sheep. A reduction of 38-87% in the transformation index of both blood and pulmonary lymph lymphocytes was observed in sheep exposed to NO2. These results suggest that intermittent, short-term exposure to 5 ppm NO2 may temporarily alter pulmonary immune responsiveness.