IN-VITRO LYMPHOCYTE PROLIFERATIVE RESPONSES AND GAMMA-INTERFERON PRODUCTION AS MEASURES OF CELL-MEDIATED-IMMUNITY OF CATTLE EXPOSED TO PASTEURELLA-HAEMOLYTICA

Cell-mediated immune mechanisms may play a role in the pathogenesis an d prevention of pneumonia in cattle caused by Pasteurella haemolytica serotype A1. To determine the circumstances required to stimulate and identify cell-mediated immune responses, calves were vaccinated with a commercial P. haemolytica bacterin or a live commercial P. haemolytic a vaccine, or were infected intratracheally with virulent P. haemolyti ca, All calves were challenge-exposed intratracheally with P. haemolyt ica 31 d after vaccination or prior infection, Peripheral blood mononu clear cells and mediastinal and superficial cervical lymph node cells were stimulated with antigens prepared from P. haemolytica to evaluate in vitro proliferative responses and gamma-interferon production as m easures of cell-mediated immunity, Strong proliferative responses and gamma-interferon production were detected in lymph node cells from cal ves vaccinated with the live vaccine and from infected calves, especia lly in response to stimulation with an outer membrane protein preparat ion from P. haemolytica, Greater proliferative responses and gamma-int erferon production were associated with the lymph node nearer the site of bacterin administration (superficial cervical lymph node) or the s ite of infection (mediastinal lymph node), whereas greater proliferati ve responses and gamma-interferon production were associated with the more distant lymph node (mediastinal lymph node) in calves vaccinated with the live vaccine, Neither proliferative responses nor gamma- inte rferon production were detected in peripheral blood mononuclear cells from calves that were vaccinated for or infected with P. haemolytica, Antileukotoxin antibody titers were determined by a serum neutralizati on assay, and protection against pneumonic lesions was more closely co rrelated with antileukotoxin antibody responses than with lymphocyte p roliferation or gamma-interferon responses.