Ehrlichia chaffeensis, a tick-transmitted rickettsial agent, causes human monocyte/macrophage-tropic ehrlichiosis. In this study, proteomic approaches were used to demonstrate host cell-specific antigenic expression by E. chaffeensis. The differentially expressed antigens include those from the 28-kDa outer membrane protein (p28-Omp) multigene locus. The proteins expressed in infected macrophages are the products of p28-Omp19 and p28-Omp20 genes, whereas in tick cells, the protein expressed is the p28-Omp14 gene product. The differentially expressed proteins are posttranslationally modified by phosphorylation and glycosylation to generate multiple expressed forms. Host cell-specific protein expression is not influenced by growth temperatures and is reversible. Host cell-specific protein expression coupled with posttranslational modifications may be a hallmark for the pathogen's adaptation to a dual-host life cycle and its persistence.

SummaryEhrlichia chaffeensis and Ehrlichia canis are ticktransmitted rickettsial pathogens that cause human and canine monocytic ehrlichiosis respectively. We tested the hypothesis that these pathogens express unique proteins in response to their growth in vertebrate and tick host cells and that this differential expression is similar in closely related Ehrlichia species. Evaluation of nine E. chaffeensis isolates and one E. canis isolate demonstrated that protein expression was host cell-dependent. The differentially expressed proteins included those from the p28/30-Omp multigene locus. E. chaffeensis and E. canis proteins expressed in infected macrophages were primarily the products of the p28-Omp 19 and 20 genes or their orthologues. In cultured tick cells, E. canis expressed only the p30-10 protein, an orthologue of the E. chaffeensis p28-Omp 14 protein which is the only protein expressed by E. chaffeensis propagated in cultured tick cells. The expressed Omp proteins were post-translationally modified to generate multiple molecular forms. E. chaffeensis gene expression from the p28/30-Omp locus was similar in tick cell lines derived from both vector ( Amblyomma americanum ) and non-vector ( Ixodes scapularis ) ticks. Differential expression of proteins within the p28/p30-Omp locus may therefore be vital for adaptation of Ehrlichia species to their dual host life cycle.

Four studies were performed to evaluate efficacy (Studies 1 and 2) and safety (Studies 3 and 4) of a novel DNA immunostimulant (Zelnate, Bayer Healthcare) in cattle. Zelnate (ZEL) was administered concurrently with (Study 1) or 24 hours after (Study 2) a Mannheimia haemolytica (Mh) challenge. Holstein steers (3 to 4 months of age; n=32/treatment, Study 1; n=40/treatment, Study 2) received either ZEL or a negative control (CON) on day 0 (Study 1) or day 1 (Study 2). Calves were challenged intratracheally with 60 mL of Mh (10 to the 7th power CFUs/mL, Study 1; 10 to the 8th power CFUs/mL, Study 2) on day 0 and clinically observed to day 5. Lung scores were obtained at the time of premature death or after necropsy on day 5. ZEL mitigated lung lesions in this Mh model, compared to the CON (Studies 1 and 2), and significantly reduced mortality compared to the CON (P < 0.05; Study 2). ZEL was shown to be safe at the injection site (Study 3) and among large populations in different field scenarios (Study 4). ZEL demonstrated efficacy by mitigating lung lesions (Studies 1 and 2) and decreasing mortality (Study 2) in this Mh disease model. Studies 3 and 4 confirmed that ZEL is safe for use in cattle.