Babesia bovis: Common protein fractions recognized by oligoclonal B-bovis-specific CD4(+) T cell lines from genetically diverse cattle

CD4(+) helper T cells are believed to be important for inducing protective immunity against Babesia bovis through the production of cytokines, includi ng IFN-gamma, that will provide help to B lymphocytes for IgG production an d activate macrophages to become parasitididal. To provide maximum protecti on in an outbred population, an effective vaccine against B, bovis should c ontain antigens that would elicit an IFN-gamma response and would be recogn ized by cattle with diverse genetic backgrounds. To identify potentially pr otective "universal" T helper (Th) cell antigens, fractions of homogenized B. bovis merozoites were tested for the ability to stimulate proliferation of oligoclonal CD4(+), IFN-gamma-producing T cell lines derived from four i mmune animals previously shown to differ in major histocompatibility comple x class II expression. Homogenized B. bovis merozoites were separated by de naturing continuous flow electrophoresis (CFE) on 15, 10, and 7.5% polyacry lamide gels into fractions containing proteins ranging from <14.5 to approx imately 95 kDa. Eighteen of 280 CFE fractions elicited anamnestic prolifera tive responses in all T cell lines tested. Nine of these cross-stimulatory fractions contained proteins of <14.5 to 24.5 kDa, and the remaining ones c ontained proteins with estimated molecular weights of 30, 31.5, 44.5, 49, 4 9.5, 54, 62, 72, and 82 kDa. Immunoblot analysis showed that four cross sti mulatory fractions contained a predicted known B. bovis antigen of similar molecular size; Previous studies had demonstrated that fractionated merozoi te proteins stimulatory for CD4+ Th cell clones had apparent molecular weig hts similar to those present in 7 of the 18 stimulatory fractions. In the p resent study, two Th cell clones responded to cross-stimulatory CFE fractio ns, underscoring the potential to use both oligoclonal and monoclonal Th ce ll lines to identify commonly recognized polypeptides as potential vaccine antigens. (C) 1999 Academic Press.