Immunological aspects of Theileria annulata infection calves. 2. Production of macrophage migration inhibition factor (MIF) by sensitized lymphocytes from Theileria annulata-infected calves.

Peripheral blood lymphocytes (PBLs) from calves infected experimentally with a stabilate of Theileria annulate, produced a factor which inhibited the migration of macrophages. This was first demonstrated against schizont antigen in some animals on day 8 post infection while in the others on day 12. The highest activity of the macrophage migration inhibition factor (MIF) was recorded on day 12 in some of the infected animals and on day 16 in the others, whereas on day 30 or more MIF was demonstrable. The MIF was also demonstrated against piroplasm antigen. 64 days after the first infection, the recovered calves were challenged with the homologous strain. It was found that PBLs from all challenged calves were able to produce MIF against both, schizont and piroplasm antigen. These results indicate occurrence of sensitized lymphocytes as effector cells of cell-mediated immunity to T. annulata infection.