650 Immune Response of Naïve Cattle to Successive Infestations of Boophilus microplus Ticks LYGIA M.F. PASSOS, a,b OSVALDO ROSSETTI, c ALICIA ARESE, c CARLOS EDDI, c JORGE CARACOSTANTOGOLO, c AND LUIS E. SAMARTINO c b Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil c INTA - CICV y A Morón, Buenos Aires, Argentina INTRODUCTION The Boophilus microplus tick is one of the most important parasites of cattle in tropical and subtropical areas, causing important economic losses. 1 The use of aca- ricides for its control is too expensive and has generated tick resistance. 2,3 Distinct tissues of B. microplus have been studied as a possible target for vaccine, 4–6 but little is known about the immunity generated after natural infestations. In this study, the immune response of cattle and some tick biological parameters were evaluated along three successive infestations. The objectives were to determine the dynamics of antibody production against tick antigenic preparations in ELISA and to characterize the antigenic patterns generated throughout the infestations using Western blot analysis. MATERIALS AND METHODS Tick Infestations Five animals were infested three times, at four-week intervals, with 75 mg of B. microplus larvæ, obtained from a hemoparasite-free colony maintained at the Insti- tuto de Patobiología–CICV-INTA). Serum samples were taken at specific times (on days 0, 3, 7, 10, 15, 21, and 28 days after each infestation) and were analyzed by ELISA and Western blotting, using an antigen prepared from larva stage. The number of detached ticks was determined and 20 engorged females from each animal were weighed, incubated individually for oviposition, and the egg mass- es were determined. Tick Antigenic Preparation Larvæ (15 days old) were disrupted in a glass homogenizer. The mixture was cen- trifuged and the supernatant sonicated. The homogenate was centrifuged and the supernatant was ultracentrifuged and separated into supernatant (soluble antigen) a Address for correspondence: Escola de Veterinária - UFMG, Caixa postal 567, Belo Horizonte, 30123-970, MG, Brazil. Voice: 55 31 3499.2092; fax: 55 31 3499.2080. lygia@dedalus.lcc.ufmg.br