Dynamics of Rickettsia-tick interactions: identification and characterization of differentially expressed mRNAs in uninfected and infected Dermacentor variabilis

To begin to explore the molecular dynamics of rickettsial tick interaction, subtractive hybridization was used to screen mRNAs in Rickettsia montanensis‐infected and uninfected Dermacentor variabilis. We isolated 30 cDNA fragments, 22 of which were up‐regulated and eight were down‐regulated in response to rickettsial infection. Based on a putative identity of 11 cDNA fragments with similarity to known protein families, the tick genetic factors have been assigned into three groups including, the tick immune response factors (α‐2 macroglobulin and IgE‐dependent histamine release factor), the receptor/adhesion molecules (the signal transducer and activator of transcription‐1/3 protein inhibitor, the clathrin adaptor protein and tetraspanin) and the stress response proteins (aldose reductase, glutathione‐S transferase, ferritin, nucleosome assembly protein and cyclin A protein). Density analyses of semiquantitative RT‐PCR amplified products demonstrated differential expression for 18 of the 23 tested genetic factors, apparently representing a 78% agreement with results obtained by subtractive hybridization. Additionally, mRNA transcripts of 17 of the 23 tested genetic factors were amplified from tick haemocytes/circulatory cells demonstrating that their expression is not restricted to the ovaries and suggesting a potential involvement in the immune response.