Molecular characterization of Ehrlichia interactions with tick cells and macrophages

Abstract

Several tick-transmitted Anaplasmataceae family rickettsiales of the genera Ehrlichia and Anaplasma have been discovered in recent years. Some are classified as pathogens responsible for emerging diseases and are a growing health concern for people. These illnesses include human monocytic ehrlichiosis, human granulocytic ewingii ehrlichiosis and human granulocytic anaplasmosis which are caused by Ehrlichia chaffeensis, E. ewingii and Anaplasma phagocytophilum, respectively. Despite the complex cellular environments of arthropod and vertebrate hosts with sophisticated defense systems, rickettsial pathogens have evolved strategies to evade host clearance and persist in vertebrate and tick hosts. For example, E. chaffeensis growing in vertebrate macrophages has distinct patterns of host cell-specific protein expression, assessed by large scale proteome analysis, and also differs considerably in its morphology compared with when it is growing in tick cells. Immunological studies suggest that host-cell-specific differences in E. chaffeensis gene expression aid the pathogen, extending its survival. Bacteria isolated from tick cells persist longer when injected into mice compared with mammalian macrophage-grown bacteria, and the host response is also significantly different. This review presents the current understanding of tick-Ehrlichia interactions at the molecular level and implications for future research in devising effective control methods.

Promoter analysis of macrophage- and tick cell-specific differentially expressed Ehrlichia chaffeensis p28-Omp genes

“…Adenine, the base found at the transcription start site for genes 14 and 19 of E. chaffeensis , appears to be the most common base at which transcription is initiated from rickettsiales genes, including pathogens of the genera Rickettsia and Anaplasma [31-34]. Our previous studies and those of other investigators also support that genes 14 and 19 are transcriptionally active independent of E. chaffeensis originating from macrophages or tick cells [9,19,21,35-38]. In the current study, quantitative RT-PCR analysis confirmed the previous observations about the presence of messages for genes 14 and 19 in both host cell backgrounds.…”

“…Recently, we reported that Ehrlichia species alter the expression of many proteins in a host cell-specific manner [18-21]. Differentially expressed proteins include outer membrane proteins made from p28-Omp multigene locus having 22 tandomly arranged paralogous genes of E. chaffeensis [18-20].…”

Human Ehrlichiosis and Anaplasmosis

“…Evaluation of different E. chaffeensis isolates demonstrated a differentially expression of p28/30-Omp proteins in infected macrophages and tick cell cultures. In infected macrophages, the dominant E. chaffeensis expressed proteins are the products of the p28-Omp 19 and 20 genes (40, 41). In cultured tick cells derived from E. chaffeensis vector, Amblyomma americanum and non-vector ( Ixodes scapularis ) ticks, E. chaffeenesis expression consists only of the p28-Omp 14 protein (40, 41).…”

“…In infected macrophages, the dominant E. chaffeensis expressed proteins are the products of the p28-Omp 19 and 20 genes (40, 41). In cultured tick cells derived from E. chaffeensis vector, Amblyomma americanum and non-vector ( Ixodes scapularis ) ticks, E. chaffeenesis expression consists only of the p28-Omp 14 protein (40, 41). It is postulated that this differential expression of proteins within the p28/p30-Omp locus may be critical for the adaptation of Ehrlichia species to their different hosts (mammals and ticks).…”

Isolation and characterization of Ehrlichia chaffeensis RNA polymerase and its use in evaluating p28 outer membrane protein gene promoters

“…Later in the developmental cycle, RBs convert back to EBs, which are released from infected cells [12,14]. The transformation of RBs to EBs by E. chaffeensis is observed in both vertebrate and tick hosts [15]. …”