ovalbumin and Tick-Infestations

The immunosuppressive effect of experimental Boophilus microplus infestation on bovine peripheral blood lymphocytes (PBL) and on host antibody production to a protein antigen (ovalbumin) was examined. Boophilus microplus infestation caused a marginal decrease in the percentage of T lymphocytes in PBL, which was observed in both lightly (5000 larvae) and heavily (40,000 larvae) infested cattle, and began at the second infestation and continued until the end of the fourth infestation. The percentage of B lymphocytes in heavily tick-infested cattle was less than that in non-infested control cattle after the fourth infestation. The response of PBL from tick-infested cattle to phytohemagglutinin (PHA) was always less than that of tick-free cattle after the second infestation. No noteworthy differences were detected between the three stages of tick infestation, that is, 1 week before the peak of adult engorgement, the middle of the peak and 1 week after all ticks had dropped. Boophilus microplus saliva (100 microliters ml-1) suppressed 47% of the response of bovine PBL to PHA in vitro. This suppressive effect of saliva may contribute to the lower responsiveness of PBL from tick-infested cattle. Antibody production by tick-infested cattle was examined during the third and fourth heavy tick infestation. Tick-infested cattle showed a diminished response against ovalbumin after the second immunization. The immunosuppressive effects of tick infestation may play an important role in tick survival or in the transmission of tick-borne diseases in the field.

Topics: Animals; Antibody Formation; Cattle; Cattle Diseases; Female; Lymphocytes; Ovalbumin; Phytohemagglutinins; Saliva; Tick Infestations

We have described functional and biochemical characteristics of a distinct T-cell dependent guinea-pig basophil-stimulating factor (BSF), measured using a sensitive 7-day bone marrow culture assay, standardized with high-activity BSF present in serum-free splenic cell-conditioned medium (CM). In the present studies, the in vivo relevance of BSF was explored during protocols of induction of peripheral blood or tissue basophil responses to ovalbumin (OA) injection or Amblyomma americanum tick feeding. Pooled immune serum, taken from OA-injected inbred or outbred animals during induction of blood and marrow basophilia, contained an in vitro inhibitor to BSF at high concentrations and BSF-like activity at low concentrations; maximal stimulation of histamine synthesis by bone marrow cells in vitro was found in the presence of Day 4 OA-immune serum. In vivo studies in the OA model demonstrated maximal serum BSF-like activity at 48-72 hr before peak bone marrow basophil response, followed by a levelling off to 50% of maximum at 2 weeks. In the tick model, serum BSF-like activity was present in Day 8, but not Day 1, post-primary infection and was maximal at Day 3 post-secondary infection; post-primary Day 1 serum was inhibitory to basophil growth in vitro. These observations suggest that BSF regulates the appearance of basophils in response to antigen in vivo by an effect on basophil progenitors. The observations stress the potential application of guinea-pig models to understanding the regulation of basophil production in allergic disorders.

Topics: Animals; Antigens; Basophils; Bone Marrow; Dose-Response Relationship, Immunologic; Female; Guinea Pigs; Histamine; Immune Sera; Kinetics; Ovalbumin; Tick Infestations; Ticks