DNA AND A CPG OLIGONUCLEOTIDE DERIVED FROM BABESIA-BOVIS ARE MITOGENIC FOR BOVINE B-CELLS

DNAs from bacteria and variety of nonvertebrate organisms, including n ematodes, mollusks, yeasts, and insects, cause polyclonal activation o f murine: B lymphocytes, Similar studies have not been reported for bo vine B cells, and to date no studies have reported mitogenic propertie s of protozoal DNA for any species. However, we and others have observ ed that protozoal parasite antigens can induce the proliferation of ly mphocytes from nonexposed donors. Extending these studies, we now show that the mitogenic property of protozoal antigen preparations is in p art attributable to parasite DNA and that Babesia bovis DNA is directl y mitogenic for bovine B cells, DNase treatment of B. bovis extracts a brogated B. bovis-induced proliferation of peripheral blood mononuclea r cells from nonexposed cattle. Like DNAs from other organisms that we re mitogenic for murine B cells, B, bovis DNA is largely nonmethylated and induced a dose-dependent proliferation of bovine B cells, which w as reduced upon methylation, Furthermore, B. bovis and E. coil DNAs en hanced immunoglobulin secretion by cultured B cells, inducing moderate increases in immunoglobulin GI and stronger increases in immunoglobul in G2, Because certain nonmethylated CpG motifs present in bacterial D NA are known to stimulate proliferation of murine and human B cells, i n Il-kb fragment of B. bovis DNA was analyzed for CG dinucleotide cont ent and for the presence of known immunostimulatory sequences (ISS) ce ntered on a CG moth, The frequency of CG dinucleotides was approximate ly one-half of the expected frequency, and several CpG hexameric seque nces with known activity for murine B cells were identified. An oligod eoxynucleotide containing one of these ISS (AACGTT), which: is present within the rhoptry-associated protein-1 (rap-1) open reading frame, w as shown to stimulate B-cell proliferation, These ISS may be involved in host immune modulation during protozoal infection and may be useful as vaccine adjuvants.