Vaccine 21 (2003) 3126–3136 Relationship between the immune response and protection conferred by new designed inactivated vaccines against ovine enzootic abortion in a mouse model Mar´ ıa R. Caro a , Nieves Ortega a , Antonio J. Buend´ ıa b , Mar´ ıa C. Gallego a , Laura Del R´ ıo a , Francisco Cuello a , Jesús Salinas a,∗ a Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain b Departamento de Histolog´ ıa y Anatom´ ıa Patológica, Facultad de Veterinaria, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain Received 23 July 2002; received in revised form 23 December 2002; accepted 25 March 2003 Abstract Chlamydophila abortus is a gram-negative obligate intracellular bacterium and the etiological agent of ovine enzootic abortion (OEA), an economically important disease in many countries. Inactivated vaccines have been reported to induce immunity in ewes and they have been used for many years. However, some outbreaks have been reported in correctly vaccinated flocks, so it is clear that new vaccines are necessary to address adequate protection and to avoid the shedding of the microorganism. This idea lead us to design inactivated vaccines, in a previously established mouse model, evaluating different inactivation procedures and new adjuvants. To assess the protection conferred, the results were analyzed on the basis of clinical signs and the isolation of C. abortus from spleen. These findings were correlated with the immune response induced by the vaccines, as determined by the production of C. abortus-specific IFN- and IL-4 from splenocyte cultures and the detection of IgG isotypes in serum. BEI was found to be the best C. abortus-inactivation procedure. The inactivated vaccines adjuvated with QS-21 (QS) or Montanide 773 (M7) induced the best protection both against homologous and heterologous challenge, with an adequate (Th1-like) immune response. Finally, these selected vaccines were evaluated in a pregnant mouse model, in which they were seen to confer good protection and to avoid the C. abortus persistence in uterus after delivery. With these results, this mouse model could be considered as an adequate tool for selecting and optimizing effective vaccines against OEA. © 2003 Elsevier Science Ltd. All rights reserved. Keywords: OEA; Chlamydophila abortus; Inactivated vaccines 1. Introduction Ovine enzootic abortion (OEA), which is caused by Chlamydophila abortus (formerly Chlamydia psittaci serotype 1) is an economically important disease in many countries. The infection of pregnant sheep and goats results in a necrotizing placentitis and consequent abortion [1]. In- activated vaccines prepared from egg-grown or cell cultures induce immunity in small ruminants and form the basis of products that have been commercially available for the pre- vention of OEA. However, the efficiency of these vaccines varies, as outbreaks have been reported in vaccinated flocks [2,3]. In fact, killed vaccines can reduce the incidence of abortion and also the shedding of C. abortus at lambing [4], although they may not stop shedding completely in ∗ Corresponding author. Tel.: +34-968-364729; fax: +34-968-364147. E-mail address: jsalinas@um.es (J. Salinas). all cases, which leads to endemic cycles of infection, that have serious consequences regarding the epidemiology of the disease. An alternative approach to solve this problem has been the development of a live temperature-sensitive attenuated vaccine [5], which is commercially available and which has been shown to offer good protection against C. abortus-induced abortion [6]. However, the potential dan- ger of live-attenuated vaccines makes them a less advisable choice, particularly since C. abortus can also cause abor- tion and severe illness in pregnant women [7]. In addition, the recent identification of new strains of C. abortus with a different antigenic structure from the vaccinal strain [8] may affect the protection for what this vaccine was de- signed. Moreover, this vaccine is licensed for sheep but not for goats, in which C. abortus remains one of the most important causes of abortion worldwide [9]. On the other hand, efforts directed at obtaining a suitable subcellular vaccine have failed. Subcellular vaccine research 0264-410X/03/$ – see front matter © 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0264-410X(03)00255-X