Characterization of protective antigens from the midgut of Amblyomma variegatum ticks J.K. KINYUA 1 , E.O. OSIR 2, * , D.O. OGOYI 1 and E.K. NGUU 1 1 Department of Biochemistry, The University of Nairobi, P.O. Box 30197, Nairobi, Kenya; 2 The Inter- national Centre for Insect Physiology and Ecology (ICIPE), P.O. Box 30772, Nairobi, Kenya; *Author for correspondence (e-mail: eosir@icipe.org) Received 13 December 2001; accepted in revised form 21 February 2002 Key words: Amblyomma variegatum, Midgut antigens, Ticks, Vaccination Abstract. Separation of midgut membrane proteins from the tick, Ambylomma variegatum, using a non- ionic detergent (Triton X-114), resulted in two protein fractions, namely DET (detergent) and AQ (aque- ous). In immunoblotting analysis with polyclonal antibodies against these fractions, 4 proteins (M r  27,000, 67,000, 86,000 and 95,000,) and 2 proteins (M r  54,000 and 67,000) were detected in the DET and AQ fractions, respectively. Three of the DET fraction proteins M r  27,000, 67,000 and 95,000 were glycosylated since they bound to the lectin, concanavalin A. In 2-dimensional gel electrophoresis, the AQ and DET fraction proteins were found to be acidic in nature. In a series of bioassay experiments, rabbits were first immunised with both DET and AQ fractions and then infested with ticks. The egg batch weights of these ticks were reduced by 50% compared to control ticks. Furthermore, there was a significant reduction in the hatchability of eggs laid by ticks fed on rabbits previously immunised with both DET (14%) and AQ (33%) fractions. Based on the egg hatchability, the reproductive capacity of ticks was reduced by 77 and 48% by DET and AQ fractions, respectively. Introduction Infestation of cattle by ticks of the genera Amblyomma constitutes a major problem for the cattle industry throughout the tropics. The tick transmits the rickettsial para- site, Cowdria ruminantium, the causative agent of heartwater (cowdriosis) in rumi- nants. Heartwater is one of the most important tick-borne diseases of cattle in southern and eastern Africa (Howell et al. 1981). Besides causing anaemia, these ticks also facilitate the development of dermatophilosis (Pegram et al. 1989). Tick control is of considerable priority globally due to the losses in livestock production and the high costs associated with control efforts (de Castro 1997; Di- peolu 1991). Although a wide variety of tick control methods have been evaluated, the use of acaricides remains the most widely used method. Despite their apparent effectiveness, acaricide use is fraught with several problems such as high costs, en- vironmental pollution and resistance development (Pegram et al. 1988). Conse- quently, there is need for alternative sustainable tick-control methods. One such method involves the use of anti-tick vaccines. The host’s ability to produce anti- bodies against the antigens of ticks and other ectoparasites has recently been ex- Experimental and Applied Acarology 26: 101–113, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.