CYTOKINES AND THE PROTECTIVE HOST IMMUNE-RESPONSE TO CHLAMYDIA-PSITTACI

The immunobiology of enzootic abortion of ewes (EAE) is incompletely u nderstood. The causative agent is Chlamydia psittaci, which infects ma ny ruminant species and has zoonotic potential. The organism can survi ve in the ovine host for many months without causing clinical symptoms but does not generate a sterile immunity during this time. It has bee n postulated that the organism persists in the host entering at a late nt phase, possibly mediated by host cytokine production. The effects o f cytokines on chlamydial multiplication vary between host species. be tween different cell types within those species and also vary between chlamydial species and strains. The multiplication of the EAE strain o f C. psittaci in ovine ST-6 cells can be restricted by interferon-gamm a (IFN-gamma) but not with comparable concentrations of IFN-alpha. Alt ering the nutrient composition of the cultures by addition of tryptoph an partially reverses the antichlamydial effects of the IFN-gamma. Thi s offers a potential mechanism by which C. psittaci can persist in she ep. The implications of these observations for the pathogenesis of EAE are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.