Correlation of hematological changes and serum and monocyte inhibition with the early suppression of phytohemagglutinin stimulation of lymphocytes in experimental infectious bursal disease.

Several experiments were conducted to study the mechanism of infectious bursal disease virus induced suppression of phytohemagglutinin stimulation of peripheral blood lymphocytes. Infectious bursal disease virus inoculation of one week old chicks resulted in significant suppression of phytohemagglutinin stimulation during the first three days after inoculation as demonstrated by a whole blood assay. Mild thymic necrosis was seen on day 3. Hematological changes during this time consisted of increased numbers of circulating lymphocytes and monocytes in infected chickens. Absolute monocyte counts remained elevated even after phytohemagglutinin stimulation had returned to normal. Furthermore, even after a 72.3% reduction in the monocyte population in leukocyte preparations, there was still marked viral induced suppression of phytohemagglutinin stimulation. An elevation in the absolute number of circulating large immature lymphocytes correlated with suppression of phytohemagglutinin stimulation. Sera from infected and control chickens depressed phytohemagglutinin stimulation of lymphocytes from control chickens at the 5 and 10% concentration. At the 1% concentration, inhibiton by control sera was considerably less than the inhibition by infected sera. The relationship between these findings and the mechanism of viral induced suppression of T-lymphocyte function is discussed.