© 2004 Blackwell Publishing Ltd 83 Parasite Immunology , 2004, 26, 83 – 93 Blackwell Publishing, Ltd. ORIGINAL ARTICLE In vivoimmunomodulatory effects In vivo immunomodulatory effects of ixodid ticks on ovine circulating T- and B-lymphocytes DHARMENDRA K. V. BOPPANA, 1 G. DHINAKAR RAJ, 2 LALITHA JOHN, 1 STEPHEN K. WIKEL, 3 B. R. LATHA 1 & S. GOMATHINAYAGAM 1 1 Department of Veterinary Parasitology and 2 Animal Biotechnology, Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai 600 007, India; and 3 Center for Microbial Pathogenesis, School of Medicine, University of Connecticut Health Center, 263 Farmington Avenue, MC3710, Farmington, CT 06030, USA SUMMARY Selected aspects of the ovine immune system were examined during the course of repeated infestations with the ixodid ticks, Haemaphysalis bispinosa and Hyalomma anatolicum anatoli- cum that naturally infest sheep, either individually or together. By the use of flow cytometry it was shown that total T-lymphocyte numbers were significantly reduced from the sixth through the ninth days of all infestations. Gamma/delta (γδ + ) and CD8 + T-lymphocytes were significantly depleted during tick feeding in all infested groups. CD4 + T-lymphocyte levels were significantly increased during secondary H. bispinosa and mixed species infestations. Hyalomma anatolicum anatolicum caused a signi- ficant increase in circulating B-lymphocytes over several days in both initial and secondary infestations. All infested sheep had increased CD4/CD8 and decreased T/B lymphocyte ratios during exposure to both ticks. Bromodeoxyuridine (BrdU) ELISA was used to measure in vitro proliferation of peripheral blood mononuclear cells stimulated with the T-lymphocyte mitogen Concanavalin A (Con A) after their collection from infested sheep. Significant suppression of in vitro proliferation occurred during first and secondary infestations with H. bispinosa, H. a. anatolicum and with both tick species together, begin- ning on the sixth day of infestation in all cases. These important tick species of sheep significantly modulate the numbers of immune effector cells and proliferation of T-lymphocytes derived from infested animals. Keywords Haemaphysalis bispinosa, Hyalomma anatolicum anatolicum, immune response, immunomodulation, ixodid tick, lymphocytes, ovine, sheep INTRODUCTION Ticks are of considerable medical and veterinary import- ance because of the diverse array of infectious agents they transmit and the direct damage they cause to skin (1,2). Ticks are the most important arthropod vectors of infec- tious agents to livestock and wildlife and are second only to mosquitoes as vectors of human pathogens (1). Previously unrecognized tick-transmitted infections are emerging together with changing importance of individual tick species as vectors of disease (3,4). Fifteen previously unrecognized tick-borne bacterial diseases have been described since the identification of Borrelia burgdorferi in 1982 (3). Control of ticks and tick-borne diseases is increasingly difficult because of the difficulties in developing effective vaccines for use in the field (5) and the widespread development of resistance to acaricides (6). Vaccine-based control of ticks became a reality with the commercial production of a recombinant vaccine against Boophilus microplus (7), but there still exists a vast untapped potential for immunological based control of ticks and for blocking their ability to transmit infectious agents. Characterizing the relationship between the tick and the host immune system is fundamental to an understanding of tick biology, pathogen transmission and the development of new methods of control, particularly for tick–host associ- ations that occur in nature. Saliva of ticks, and other blood- feeding arthropods, contains numerous pharmacologically active molecules essential for successful blood feeding and transmission of infectious agents (8–10). Saliva protein profiles change during the course of engorgement (11,12), exposing the host to different antigens in a temporal manner and stimulating host immune responses (13). Ticks are well recognized for their ability to modulate host innate and specific acquired immune defences (10,14,15) reflecting the evolution of tick–host relationships. Both B- and T-lymphocytes are central to immunity to ticks (13) and targets for tick-induced immune modulation (14,15). Correspondence: Dharmendra K. V. Boppana, Department of Veterinary Parasitology, NTR College of Veterinary Science, Gannavaram, Krishna District, Andhra Pradesh 521 102, India (e-mail: dboppana@yahoo.com). Accepted for publication: 31 March 2004