Lymphocyte reactivity to Ostertagia ostertagi L3 antigen in type I ostertagiasis.

To better understand the immune response of calves infected with Ostertagia ostertagi, studies were conducted to examine cell-mediated immune responses to L3 antigen and phytohemagglutinin (PHA) by lymphocyte reactivity assay. The L3 antigen was prepared by freeze-thawing and sonication of exsheathed O ostertagi L3. Antigen preparations contained 40 to 60 micrograms of protein/ml and no detectable endotoxin. Cell-mediated immune responses of peripheral blood lymphocytes were determined in 3 groups of 12 calves each: (i) calves given consecutive multiple dose inoculations with L3; (ii) noninfected controls. Consecutive multiple-dose-inoculated calves showed marked increases in stimulation indices (SI) to L3 antigen over the SI of naturally inoculated calves (56.5 and 25.8, respectively). Negative SI were obtained in calves of the noninoculated control group (-1.0). No significant difference (P greater than or equal to 0.05) in response to PHA was obtained between lymphocytes from calves inoculated with O ostertagi and lymphocytes obtained from noninoculated control calves. There was significant (P less than or equal to 0.01) agreement between positive SI and evidence of patent infection (development of type I ostertagiasis). Specificity of lymphocyte reactivity was determined, using lymphocytes from 4 O ostertagi- and 2 Cooperia punctata-infected calves after challenge inoculation. Positive SI to L3 antigen were obtained, using lymphocytes from either O ostertagi- or C punctata-infected calves, indicating that there may be a lack of genus specificity for O ostertagi L3 antigen in lymphocyte reactivity assay. Kinetic studies of lymphocyte reactivity to L3 antigen and PHA showed that responses were briefly suppressed to both of these stimuli in prepatent calves.(ABSTRACT TRUNCATED AT 250 WORDS)