Identification of Cowdria ruminantium antigens that stimulate proliferation of lymphocytes from cattle immunized by infection and treatment or with inactivated organisms

Cowdria ruminantium is an obligate intracellular pathogen that causes heart water in ruminants. Several findings suggest that T cells play an important role in protection against the disease. In order to identify which protein s are involved in T-cell immunity, C. ruminantium proteins were fractionate d by continuous-flow electrophoresis and tested for their ability to stimul ate lymphocyte proliferation in vitro. C, ruminantium-infected endothelial cell lysates were fractionated at between 11 and 38 kDa and 50 and 168 kDa on 15 and 7% acrylamide gels, respectively. In an attempt to stimulate the natural infective process, peripheral blood mononuclear cells (PBMC) were o btained from two cattle rendered immune by infection and treatment and assa yed in proliferation assays with fractionated proteins. In a parallel study , four cattle were immunized with inactivated C, ruminantium to determine w hether their lymphocytes also responded to fractionated proteins. Prolifera tion assays after immunization by infection and treatment detected no C, ru minantium-specific proliferation in vitro after one vaccination. Proliferat ion was observed, however, between 1 and 4 weeks after challenge. This was followed by a period of no detectable response, after which the response re appeared. PBMC from animals immunized with inactivated organisms proliferat ed specifically in response to antigen soon after the first immunization. O nly C, ruminantium proteins with low molecular masses of 11, 12, 14 to 17, and 19 to 23 kDa induced proliferative responses by lymphocytes from all si x animals. These protein fractions may have potential as vaccine antigens.